githubmirror/cpython

Modules/_struct.c
2 669 строк74 KB
Serhiy Storchaka
[3.13] gh-85943: Fix BytesWarning in the struct format cache under -bb (GH-153627) (GH-153836)
17 июл 2026, 11:26
17 июл 2026, 11:26c8a0fbf
/* struct module -- pack values into and (out of) bytes objects */

/* New version supporting byte order, alignment and size options,
   byte strings, and unsigned numbers */

#ifndef Py_BUILD_CORE_BUILTIN
#  define Py_BUILD_CORE_MODULE 1
#endif

#include "Python.h"
#include "pycore_bytesobject.h"   // _PyBytesWriter
#include "pycore_long.h"          // _PyLong_AsByteArray()
#include "pycore_moduleobject.h"  // _PyModule_GetState()
#include "pycore_weakref.h"       // FT_CLEAR_WEAKREFS()

#include <stddef.h>               // offsetof()

/*[clinic input]
class Struct "PyStructObject *" "&PyStructType"
[clinic start generated code]*/
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=9b032058a83ed7c3]*/

typedef struct {
    PyObject *cache;
    PyObject *PyStructType;
    PyObject *unpackiter_type;
    PyObject *StructError;
} _structmodulestate;

static inline _structmodulestate*
get_struct_state(PyObject *module)
{
    void *state = _PyModule_GetState(module);
    assert(state != NULL);
    return (_structmodulestate *)state;
}

static struct PyModuleDef _structmodule;

#define get_struct_state_structinst(self) \
    (get_struct_state(PyType_GetModuleByDef(Py_TYPE(self), &_structmodule)))
#define get_struct_state_iterinst(self) \
    (get_struct_state(PyType_GetModule(Py_TYPE(self))))

/* The translation function for each format character is table driven */
typedef struct _formatdef {
    char format;
    Py_ssize_t size;
    Py_ssize_t alignment;
    PyObject* (*unpack)(_structmodulestate *, const char *,
                        const struct _formatdef *);
    int (*pack)(_structmodulestate *, char *, PyObject *,
                const struct _formatdef *);
} formatdef;

typedef struct _formatcode {
    const struct _formatdef *fmtdef;
    Py_ssize_t offset;
    Py_ssize_t size;
    Py_ssize_t repeat;
} formatcode;

/* Struct object interface */

typedef struct {
    PyObject_HEAD
    Py_ssize_t s_size;
    Py_ssize_t s_len;
    formatcode *s_codes;
    PyObject *s_format;
    PyObject *weakreflist; /* List of weak references */
} PyStructObject;

#define PyStruct_Check(op, state) PyObject_TypeCheck(op, (PyTypeObject *)(state)->PyStructType)

/* Define various structs to figure out the alignments of types */


typedef struct { char c; short x; } st_short;
typedef struct { char c; int x; } st_int;
typedef struct { char c; long x; } st_long;
typedef struct { char c; float x; } st_float;
typedef struct { char c; double x; } st_double;
typedef struct { char c; void *x; } st_void_p;
typedef struct { char c; size_t x; } st_size_t;
typedef struct { char c; _Bool x; } st_bool;

#define SHORT_ALIGN (sizeof(st_short) - sizeof(short))
#define INT_ALIGN (sizeof(st_int) - sizeof(int))
#define LONG_ALIGN (sizeof(st_long) - sizeof(long))
#define FLOAT_ALIGN (sizeof(st_float) - sizeof(float))
#define DOUBLE_ALIGN (sizeof(st_double) - sizeof(double))
#define VOID_P_ALIGN (sizeof(st_void_p) - sizeof(void *))
#define SIZE_T_ALIGN (sizeof(st_size_t) - sizeof(size_t))
#define BOOL_ALIGN (sizeof(st_bool) - sizeof(_Bool))

/* We can't support q and Q in native mode unless the compiler does;
   in std mode, they're 8 bytes on all platforms. */
typedef struct { char c; long long x; } s_long_long;
#define LONG_LONG_ALIGN (sizeof(s_long_long) - sizeof(long long))

#ifdef __powerc
#pragma options align=reset
#endif

/*[python input]
class cache_struct_converter(CConverter):
    type = 'PyStructObject *'
    converter = 'cache_struct_converter'
    c_default = "NULL"
    broken_limited_capi = True

    def parse_arg(self, argname, displayname, *, limited_capi):
        assert not limited_capi
        return self.format_code("""
            if (!{converter}(module, {argname}, &{paramname})) {{{{
                goto exit;
            }}}}
            """,
            argname=argname,
            converter=self.converter)

    def cleanup(self):
        return "Py_XDECREF(%s);\n" % self.name
[python start generated code]*/
/*[python end generated code: output=da39a3ee5e6b4b0d input=c33b27d6b06006c6]*/

static int cache_struct_converter(PyObject *, PyObject *, PyStructObject **);

#include "clinic/_struct.c.h"

/* Helper for integer format codes: converts an arbitrary Python object to a
   PyLongObject if possible, otherwise fails.  Caller should decref. */

static PyObject *
get_pylong(_structmodulestate *state, PyObject *v)
{
    assert(v != NULL);
    if (!PyLong_Check(v)) {
        /* Not an integer;  try to use __index__ to convert. */
        if (PyIndex_Check(v)) {
            v = _PyNumber_Index(v);
            if (v == NULL)
                return NULL;
        }
        else {
            PyErr_SetString(state->StructError,
                            "required argument is not an integer");
            return NULL;
        }
    }
    else
        Py_INCREF(v);

    assert(PyLong_Check(v));
    return v;
}

/* Helper routine to get a C long and raise the appropriate error if it isn't
   one */

static int
get_long(_structmodulestate *state, PyObject *v, long *p)
{
    long x;

    v = get_pylong(state, v);
    if (v == NULL)
        return -1;
    assert(PyLong_Check(v));
    x = PyLong_AsLong(v);
    Py_DECREF(v);
    if (x == (long)-1 && PyErr_Occurred()) {
        return -1;
    }
    *p = x;
    return 0;
}


/* Same, but handling unsigned long */

static int
get_ulong(_structmodulestate *state, PyObject *v, unsigned long *p)
{
    unsigned long x;

    v = get_pylong(state, v);
    if (v == NULL)
        return -1;
    assert(PyLong_Check(v));
    x = PyLong_AsUnsignedLong(v);
    Py_DECREF(v);
    if (x == (unsigned long)-1 && PyErr_Occurred()) {
        return -1;
    }
    *p = x;
    return 0;
}

/* Same, but handling native long long. */

static int
get_longlong(_structmodulestate *state, PyObject *v, long long *p)
{
    long long x;

    v = get_pylong(state, v);
    if (v == NULL)
        return -1;
    assert(PyLong_Check(v));
    x = PyLong_AsLongLong(v);
    Py_DECREF(v);
    if (x == (long long)-1 && PyErr_Occurred()) {
        return -1;
    }
    *p = x;
    return 0;
}

/* Same, but handling native unsigned long long. */

static int
get_ulonglong(_structmodulestate *state, PyObject *v, unsigned long long *p)
{
    unsigned long long x;

    v = get_pylong(state, v);
    if (v == NULL)
        return -1;
    assert(PyLong_Check(v));
    x = PyLong_AsUnsignedLongLong(v);
    Py_DECREF(v);
    if (x == (unsigned long long)-1 && PyErr_Occurred()) {
        return -1;
    }
    *p = x;
    return 0;
}

/* Same, but handling Py_ssize_t */

static int
get_ssize_t(_structmodulestate *state, PyObject *v, Py_ssize_t *p)
{
    Py_ssize_t x;

    v = get_pylong(state, v);
    if (v == NULL)
        return -1;
    assert(PyLong_Check(v));
    x = PyLong_AsSsize_t(v);
    Py_DECREF(v);
    if (x == (Py_ssize_t)-1 && PyErr_Occurred()) {
        return -1;
    }
    *p = x;
    return 0;
}

/* Same, but handling size_t */

static int
get_size_t(_structmodulestate *state, PyObject *v, size_t *p)
{
    size_t x;

    v = get_pylong(state, v);
    if (v == NULL)
        return -1;
    assert(PyLong_Check(v));
    x = PyLong_AsSize_t(v);
    Py_DECREF(v);
    if (x == (size_t)-1 && PyErr_Occurred()) {
        return -1;
    }
    *p = x;
    return 0;
}


#define RANGE_ERROR(state, f, flag) return _range_error(state, f, flag)


/* Floating-point helpers */

static PyObject *
unpack_halffloat(const char *p,  /* start of 2-byte string */
                 int le)         /* true for little-endian, false for big-endian */
{
    double x = PyFloat_Unpack2(p, le);
    if (x == -1.0 && PyErr_Occurred()) {
        return NULL;
    }
    return PyFloat_FromDouble(x);
}

static int
pack_halffloat(_structmodulestate *state,
               char *p,      /* start of 2-byte string */
               PyObject *v,  /* value to pack */
               int le)       /* true for little-endian, false for big-endian */
{
    double x = PyFloat_AsDouble(v);
    if (x == -1.0 && PyErr_Occurred()) {
        PyErr_SetString(state->StructError,
                        "required argument is not a float");
        return -1;
    }
    return PyFloat_Pack2(x, p, le);
}

static PyObject *
unpack_float(const char *p,  /* start of 4-byte string */
         int le)             /* true for little-endian, false for big-endian */
{
    double x;

    x = PyFloat_Unpack4(p, le);
    if (x == -1.0 && PyErr_Occurred())
        return NULL;
    return PyFloat_FromDouble(x);
}

static PyObject *
unpack_double(const char *p,  /* start of 8-byte string */
          int le)         /* true for little-endian, false for big-endian */
{
    double x;

    x = PyFloat_Unpack8(p, le);
    if (x == -1.0 && PyErr_Occurred())
        return NULL;
    return PyFloat_FromDouble(x);
}

/* Helper to format the range error exceptions */
static int
_range_error(_structmodulestate *state, const formatdef *f, int is_unsigned)
{
    /* ulargest is the largest unsigned value with f->size bytes.
     * Note that the simpler:
     *     ((size_t)1 << (f->size * 8)) - 1
     * doesn't work when f->size == sizeof(size_t) because C doesn't
     * define what happens when a left shift count is >= the number of
     * bits in the integer being shifted; e.g., on some boxes it doesn't
     * shift at all when they're equal.
     */
    const size_t ulargest = (size_t)-1 >> ((SIZEOF_SIZE_T - f->size)*8);
    assert(f->size >= 1 && f->size <= SIZEOF_SIZE_T);
    if (is_unsigned)
        PyErr_Format(state->StructError,
            "'%c' format requires 0 <= number <= %zu",
            f->format,
            ulargest);
    else {
        const Py_ssize_t largest = (Py_ssize_t)(ulargest >> 1);
        PyErr_Format(state->StructError,
            "'%c' format requires %zd <= number <= %zd",
            f->format,
            ~ largest,
            largest);
    }

    return -1;
}



/* A large number of small routines follow, with names of the form

   [bln][up]_TYPE

   [bln] distinguishes among big-endian, little-endian and native.
   [pu] distinguishes between pack (to struct) and unpack (from struct).
   TYPE is one of char, byte, ubyte, etc.
*/

/* Native mode routines. ****************************************************/
/* NOTE:
   In all n[up]_<type> routines handling types larger than 1 byte, there is
   *no* guarantee that the p pointer is properly aligned for each type,
   therefore memcpy is called.  An intermediate variable is used to
   compensate for big-endian architectures.
   Normally both the intermediate variable and the memcpy call will be
   skipped by C optimisation in little-endian architectures (gcc >= 2.91
   does this). */

static PyObject *
nu_char(_structmodulestate *state, const char *p, const formatdef *f)
{
    return PyBytes_FromStringAndSize(p, 1);
}

static PyObject *
nu_byte(_structmodulestate *state, const char *p, const formatdef *f)
{
    return PyLong_FromLong((long) *(signed char *)p);
}

static PyObject *
nu_ubyte(_structmodulestate *state, const char *p, const formatdef *f)
{
    return PyLong_FromLong((long) *(unsigned char *)p);
}

static PyObject *
nu_short(_structmodulestate *state, const char *p, const formatdef *f)
{
    short x;
    memcpy((char *)&x, p, sizeof x);
    return PyLong_FromLong((long)x);
}

static PyObject *
nu_ushort(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned short x;
    memcpy((char *)&x, p, sizeof x);
    return PyLong_FromLong((long)x);
}

static PyObject *
nu_int(_structmodulestate *state, const char *p, const formatdef *f)
{
    int x;
    memcpy((char *)&x, p, sizeof x);
    return PyLong_FromLong((long)x);
}

static PyObject *
nu_uint(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned int x;
    memcpy((char *)&x, p, sizeof x);
    return PyLong_FromUnsignedLong((unsigned long)x);
}

static PyObject *
nu_long(_structmodulestate *state, const char *p, const formatdef *f)
{
    long x;
    memcpy((char *)&x, p, sizeof x);
    return PyLong_FromLong(x);
}

static PyObject *
nu_ulong(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long x;
    memcpy((char *)&x, p, sizeof x);
    return PyLong_FromUnsignedLong(x);
}

static PyObject *
nu_ssize_t(_structmodulestate *state, const char *p, const formatdef *f)
{
    Py_ssize_t x;
    memcpy((char *)&x, p, sizeof x);
    return PyLong_FromSsize_t(x);
}

static PyObject *
nu_size_t(_structmodulestate *state, const char *p, const formatdef *f)
{
    size_t x;
    memcpy((char *)&x, p, sizeof x);
    return PyLong_FromSize_t(x);
}

static PyObject *
nu_longlong(_structmodulestate *state, const char *p, const formatdef *f)
{
    long long x;
    memcpy((char *)&x, p, sizeof x);
    return PyLong_FromLongLong(x);
}

static PyObject *
nu_ulonglong(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long long x;
    memcpy((char *)&x, p, sizeof x);
    return PyLong_FromUnsignedLongLong(x);
}

static PyObject *
nu_bool(_structmodulestate *state, const char *p, const formatdef *f)
{
    const _Bool bool_false = 0;
    return PyBool_FromLong(memcmp(p, &bool_false, sizeof(_Bool)));
}


static PyObject *
nu_halffloat(_structmodulestate *state, const char *p, const formatdef *f)
{
#if PY_LITTLE_ENDIAN
    return unpack_halffloat(p, 1);
#else
    return unpack_halffloat(p, 0);
#endif
}

static PyObject *
nu_float(_structmodulestate *state, const char *p, const formatdef *f)
{
    float x;
    memcpy((char *)&x, p, sizeof x);
    return PyFloat_FromDouble((double)x);
}

static PyObject *
nu_double(_structmodulestate *state, const char *p, const formatdef *f)
{
    double x;
    memcpy((char *)&x, p, sizeof x);
    return PyFloat_FromDouble(x);
}

static PyObject *
nu_void_p(_structmodulestate *state, const char *p, const formatdef *f)
{
    void *x;
    memcpy((char *)&x, p, sizeof x);
    return PyLong_FromVoidPtr(x);
}

static int
np_byte(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    long x;
    if (get_long(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 0);
        }
        return -1;
    }
    if (x < -128 || x > 127) {
        RANGE_ERROR(state, f, 0);
    }
    *p = (char)x;
    return 0;
}

static int
np_ubyte(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    long x;
    if (get_long(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 1);
        }
        return -1;
    }
    if (x < 0 || x > 255) {
        RANGE_ERROR(state, f, 1);
    }
    *(unsigned char *)p = (unsigned char)x;
    return 0;
}

static int
np_char(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    if (!PyBytes_Check(v) || PyBytes_Size(v) != 1) {
        PyErr_SetString(state->StructError,
                        "char format requires a bytes object of length 1");
        return -1;
    }
    *p = *PyBytes_AS_STRING(v);
    return 0;
}

static int
np_short(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    long x;
    short y;
    if (get_long(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 0);
        }
        return -1;
    }
    if (x < SHRT_MIN || x > SHRT_MAX) {
        RANGE_ERROR(state, f, 0);
    }
    y = (short)x;
    memcpy(p, (char *)&y, sizeof y);
    return 0;
}

static int
np_ushort(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    long x;
    unsigned short y;
    if (get_long(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 1);
        }
        return -1;
    }
    if (x < 0 || x > USHRT_MAX) {
        RANGE_ERROR(state, f, 1);
    }
    y = (unsigned short)x;
    memcpy(p, (char *)&y, sizeof y);
    return 0;
}

static int
np_int(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    long x;
    int y;
    if (get_long(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 0);
        }
        return -1;
    }
#if (SIZEOF_LONG > SIZEOF_INT)
    if ((x < ((long)INT_MIN)) || (x > ((long)INT_MAX)))
        RANGE_ERROR(state, f, 0);
#endif
    y = (int)x;
    memcpy(p, (char *)&y, sizeof y);
    return 0;
}

static int
np_uint(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    unsigned long x;
    unsigned int y;
    if (get_ulong(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 1);
        }
        return -1;
    }
    y = (unsigned int)x;
#if (SIZEOF_LONG > SIZEOF_INT)
    if (x > ((unsigned long)UINT_MAX))
        RANGE_ERROR(state, f, 1);
#endif
    memcpy(p, (char *)&y, sizeof y);
    return 0;
}

static int
np_long(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    long x;
    if (get_long(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 0);
        }
        return -1;
    }
    memcpy(p, (char *)&x, sizeof x);
    return 0;
}

static int
np_ulong(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    unsigned long x;
    if (get_ulong(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 1);
        }
        return -1;
    }
    memcpy(p, (char *)&x, sizeof x);
    return 0;
}

static int
np_ssize_t(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    Py_ssize_t x;
    if (get_ssize_t(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 0);
        }
        return -1;
    }
    memcpy(p, (char *)&x, sizeof x);
    return 0;
}

static int
np_size_t(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    size_t x;
    if (get_size_t(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 1);
        }
        return -1;
    }
    memcpy(p, (char *)&x, sizeof x);
    return 0;
}

static int
np_longlong(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    long long x;
    if (get_longlong(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            PyErr_Format(state->StructError,
                         "'%c' format requires %lld <= number <= %lld",
                         f->format,
                         LLONG_MIN,
                         LLONG_MAX);
        }
        return -1;
    }
    memcpy(p, (char *)&x, sizeof x);
    return 0;
}

static int
np_ulonglong(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    unsigned long long x;
    if (get_ulonglong(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            PyErr_Format(state->StructError,
                         "'%c' format requires 0 <= number <= %llu",
                         f->format,
                         ULLONG_MAX);
        }
        return -1;
    }
    memcpy(p, (char *)&x, sizeof x);
    return 0;
}


static int
np_bool(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    int y;
    _Bool x;
    y = PyObject_IsTrue(v);
    if (y < 0)
        return -1;
    x = y;
    memcpy(p, (char *)&x, sizeof x);
    return 0;
}

static int
np_halffloat(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
#if PY_LITTLE_ENDIAN
    return pack_halffloat(state, p, v, 1);
#else
    return pack_halffloat(state, p, v, 0);
#endif
}

static int
np_float(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    double x = PyFloat_AsDouble(v);
    if (x == -1 && PyErr_Occurred()) {
        PyErr_SetString(state->StructError,
                        "required argument is not a float");
        return -1;
    }
    return PyFloat_Pack4(x, p, PY_LITTLE_ENDIAN);
}

static int
np_double(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    double x = PyFloat_AsDouble(v);
    if (x == -1 && PyErr_Occurred()) {
        PyErr_SetString(state->StructError,
                        "required argument is not a float");
        return -1;
    }
    memcpy(p, (char *)&x, sizeof(double));
    return 0;
}

static int
np_void_p(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    void *x;

    v = get_pylong(state, v);
    if (v == NULL)
        return -1;
    assert(PyLong_Check(v));
    x = PyLong_AsVoidPtr(v);
    Py_DECREF(v);
    if (x == NULL && PyErr_Occurred())
        return -1;
    memcpy(p, (char *)&x, sizeof x);
    return 0;
}

static const formatdef native_table[] = {
    {'x',       sizeof(char),   0,              NULL},
    {'b',       sizeof(char),   0,              nu_byte,        np_byte},
    {'B',       sizeof(char),   0,              nu_ubyte,       np_ubyte},
    {'c',       sizeof(char),   0,              nu_char,        np_char},
    {'s',       sizeof(char),   0,              NULL},
    {'p',       sizeof(char),   0,              NULL},
    {'h',       sizeof(short),  SHORT_ALIGN,    nu_short,       np_short},
    {'H',       sizeof(short),  SHORT_ALIGN,    nu_ushort,      np_ushort},
    {'i',       sizeof(int),    INT_ALIGN,      nu_int,         np_int},
    {'I',       sizeof(int),    INT_ALIGN,      nu_uint,        np_uint},
    {'l',       sizeof(long),   LONG_ALIGN,     nu_long,        np_long},
    {'L',       sizeof(long),   LONG_ALIGN,     nu_ulong,       np_ulong},
    {'n',       sizeof(size_t), SIZE_T_ALIGN,   nu_ssize_t,     np_ssize_t},
    {'N',       sizeof(size_t), SIZE_T_ALIGN,   nu_size_t,      np_size_t},
    {'q',       sizeof(long long), LONG_LONG_ALIGN, nu_longlong, np_longlong},
    {'Q',       sizeof(long long), LONG_LONG_ALIGN, nu_ulonglong,np_ulonglong},
    {'?',       sizeof(_Bool),      BOOL_ALIGN,     nu_bool,        np_bool},
    {'e',       sizeof(short),  SHORT_ALIGN,    nu_halffloat,   np_halffloat},
    {'f',       sizeof(float),  FLOAT_ALIGN,    nu_float,       np_float},
    {'d',       sizeof(double), DOUBLE_ALIGN,   nu_double,      np_double},
    {'P',       sizeof(void *), VOID_P_ALIGN,   nu_void_p,      np_void_p},
    {0}
};

/* Big-endian routines. *****************************************************/

static PyObject *
bu_short(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long x = 0;

    /* This function is only ever used in the case f->size == 2. */
    assert(f->size == 2);
    Py_ssize_t i = 2;
    const unsigned char *bytes = (const unsigned char *)p;
    do {
        x = (x<<8) | *bytes++;
    } while (--i > 0);
    /* Extend sign, avoiding implementation-defined or undefined behaviour. */
    x = (x ^ 0x8000U) - 0x8000U;
    return PyLong_FromLong(x & 0x8000U ? -1 - (long)(~x) : (long)x);
}

static PyObject *
bu_int(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long x = 0;

    /* This function is only ever used in the case f->size == 4. */
    assert(f->size == 4);
    Py_ssize_t i = 4;
    const unsigned char *bytes = (const unsigned char *)p;
    do {
        x = (x<<8) | *bytes++;
    } while (--i > 0);
    /* Extend sign, avoiding implementation-defined or undefined behaviour. */
    x = (x ^ 0x80000000U) - 0x80000000U;
    return PyLong_FromLong(x & 0x80000000U ? -1 - (long)(~x) : (long)x);
}

static PyObject *
bu_uint(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long x = 0;
    Py_ssize_t i = f->size;
    const unsigned char *bytes = (const unsigned char *)p;
    do {
        x = (x<<8) | *bytes++;
    } while (--i > 0);
    return PyLong_FromUnsignedLong(x);
}

static PyObject *
bu_longlong(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long long x = 0;

    /* This function is only ever used in the case f->size == 8. */
    assert(f->size == 8);
    Py_ssize_t i = 8;
    const unsigned char *bytes = (const unsigned char *)p;
    do {
        x = (x<<8) | *bytes++;
    } while (--i > 0);
    /* Extend sign, avoiding implementation-defined or undefined behaviour. */
    x = (x ^ 0x8000000000000000U) - 0x8000000000000000U;
    return PyLong_FromLongLong(
        x & 0x8000000000000000U ? -1 - (long long)(~x) : (long long)x);
}

static PyObject *
bu_ulonglong(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long long x = 0;
    Py_ssize_t i = f->size;
    const unsigned char *bytes = (const unsigned char *)p;
    do {
        x = (x<<8) | *bytes++;
    } while (--i > 0);
    return PyLong_FromUnsignedLongLong(x);
}

static PyObject *
bu_halffloat(_structmodulestate *state, const char *p, const formatdef *f)
{
    return unpack_halffloat(p, 0);
}

static PyObject *
bu_float(_structmodulestate *state, const char *p, const formatdef *f)
{
    return unpack_float(p, 0);
}

static PyObject *
bu_double(_structmodulestate *state, const char *p, const formatdef *f)
{
    return unpack_double(p, 0);
}

static PyObject *
bu_bool(_structmodulestate *state, const char *p, const formatdef *f)
{
    return PyBool_FromLong(*p != 0);
}

static int
bp_int(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    long x;
    Py_ssize_t i;
    unsigned char *q = (unsigned char *)p;
    if (get_long(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 0);
        }
        return -1;
    }
    i = f->size;
    if (i != SIZEOF_LONG) {
        if ((i == 2) && (x < -32768 || x > 32767))
            RANGE_ERROR(state, f, 0);
#if (SIZEOF_LONG != 4)
        else if ((i == 4) && (x < -2147483648L || x > 2147483647L))
            RANGE_ERROR(state, f, 0);
#endif
    }
    do {
        q[--i] = (unsigned char)(x & 0xffL);
        x >>= 8;
    } while (i > 0);
    return 0;
}

static int
bp_uint(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    unsigned long x;
    Py_ssize_t i;
    unsigned char *q = (unsigned char *)p;
    if (get_ulong(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 1);
        }
        return -1;
    }
    i = f->size;
    if (i != SIZEOF_LONG) {
        unsigned long maxint = 1;
        maxint <<= (unsigned long)(i * 8);
        if (x >= maxint)
            RANGE_ERROR(state, f, 1);
    }
    do {
        q[--i] = (unsigned char)(x & 0xffUL);
        x >>= 8;
    } while (i > 0);
    return 0;
}

static int
bp_longlong(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    int res;
    v = get_pylong(state, v);
    if (v == NULL)
        return -1;
    res = _PyLong_AsByteArray((PyLongObject *)v,
                              (unsigned char *)p,
                              8,
                              0, /* little_endian */
                              1, /* signed */
                              0  /* !with_exceptions */);
    Py_DECREF(v);
    if (res < 0) {
        PyErr_Format(state->StructError,
                     "'%c' format requires %lld <= number <= %lld",
                     f->format,
                     LLONG_MIN,
                     LLONG_MAX);
        return -1;
    }
    return res;
}

static int
bp_ulonglong(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    int res;
    v = get_pylong(state, v);
    if (v == NULL)
        return -1;
    res = _PyLong_AsByteArray((PyLongObject *)v,
                              (unsigned char *)p,
                              8,
                              0, /* little_endian */
                              0, /* signed */
                              0  /* !with_exceptions */);
    Py_DECREF(v);
    if (res < 0) {
        PyErr_Format(state->StructError,
                     "'%c' format requires 0 <= number <= %llu",
                     f->format,
                     ULLONG_MAX);
        return -1;
    }
    return res;
}

static int
bp_halffloat(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    return pack_halffloat(state, p, v, 0);
}

static int
bp_float(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    double x = PyFloat_AsDouble(v);
    if (x == -1 && PyErr_Occurred()) {
        PyErr_SetString(state->StructError,
                        "required argument is not a float");
        return -1;
    }
    return PyFloat_Pack4(x, p, 0);
}

static int
bp_double(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    double x = PyFloat_AsDouble(v);
    if (x == -1 && PyErr_Occurred()) {
        PyErr_SetString(state->StructError,
                        "required argument is not a float");
        return -1;
    }
    return PyFloat_Pack8(x, p, 0);
}

static int
bp_bool(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    int y;
    y = PyObject_IsTrue(v);
    if (y < 0)
        return -1;
    *p = (char)y;
    return 0;
}

static formatdef bigendian_table[] = {
    {'x',       1,              0,              NULL},
    {'b',       1,              0,              nu_byte,        np_byte},
    {'B',       1,              0,              nu_ubyte,       np_ubyte},
    {'c',       1,              0,              nu_char,        np_char},
    {'s',       1,              0,              NULL},
    {'p',       1,              0,              NULL},
    {'h',       2,              0,              bu_short,       bp_int},
    {'H',       2,              0,              bu_uint,        bp_uint},
    {'i',       4,              0,              bu_int,         bp_int},
    {'I',       4,              0,              bu_uint,        bp_uint},
    {'l',       4,              0,              bu_int,         bp_int},
    {'L',       4,              0,              bu_uint,        bp_uint},
    {'q',       8,              0,              bu_longlong,    bp_longlong},
    {'Q',       8,              0,              bu_ulonglong,   bp_ulonglong},
    {'?',       1,              0,              bu_bool,        bp_bool},
    {'e',       2,              0,              bu_halffloat,   bp_halffloat},
    {'f',       4,              0,              bu_float,       bp_float},
    {'d',       8,              0,              bu_double,      bp_double},
    {0}
};

/* Little-endian routines. *****************************************************/

static PyObject *
lu_short(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long x = 0;

    /* This function is only ever used in the case f->size == 2. */
    assert(f->size == 2);
    Py_ssize_t i = 2;
    const unsigned char *bytes = (const unsigned char *)p;
    do {
        x = (x<<8) | bytes[--i];
    } while (i > 0);
    /* Extend sign, avoiding implementation-defined or undefined behaviour. */
    x = (x ^ 0x8000U) - 0x8000U;
    return PyLong_FromLong(x & 0x8000U ? -1 - (long)(~x) : (long)x);
}

static PyObject *
lu_int(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long x = 0;

    /* This function is only ever used in the case f->size == 4. */
    assert(f->size == 4);
    Py_ssize_t i = 4;
    const unsigned char *bytes = (const unsigned char *)p;
    do {
        x = (x<<8) | bytes[--i];
    } while (i > 0);
    /* Extend sign, avoiding implementation-defined or undefined behaviour. */
    x = (x ^ 0x80000000U) - 0x80000000U;
    return PyLong_FromLong(x & 0x80000000U ? -1 - (long)(~x) : (long)x);
}

static PyObject *
lu_uint(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long x = 0;
    Py_ssize_t i = f->size;
    const unsigned char *bytes = (const unsigned char *)p;
    do {
        x = (x<<8) | bytes[--i];
    } while (i > 0);
    return PyLong_FromUnsignedLong(x);
}

static PyObject *
lu_longlong(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long long x = 0;

    /* This function is only ever used in the case f->size == 8. */
    assert(f->size == 8);
    Py_ssize_t i = 8;
    const unsigned char *bytes = (const unsigned char *)p;
    do {
        x = (x<<8) | bytes[--i];
    } while (i > 0);
    /* Extend sign, avoiding implementation-defined or undefined behaviour. */
    x = (x ^ 0x8000000000000000U) - 0x8000000000000000U;
    return PyLong_FromLongLong(
        x & 0x8000000000000000U ? -1 - (long long)(~x) : (long long)x);
}

static PyObject *
lu_ulonglong(_structmodulestate *state, const char *p, const formatdef *f)
{
    unsigned long long x = 0;
    Py_ssize_t i = f->size;
    const unsigned char *bytes = (const unsigned char *)p;
    do {
        x = (x<<8) | bytes[--i];
    } while (i > 0);
    return PyLong_FromUnsignedLongLong(x);
}

static PyObject *
lu_halffloat(_structmodulestate *state, const char *p, const formatdef *f)
{
    return unpack_halffloat(p, 1);
}

static PyObject *
lu_float(_structmodulestate *state, const char *p, const formatdef *f)
{
    return unpack_float(p, 1);
}

static PyObject *
lu_double(_structmodulestate *state, const char *p, const formatdef *f)
{
    return unpack_double(p, 1);
}

static int
lp_int(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    long x;
    Py_ssize_t i;
    unsigned char *q = (unsigned char *)p;
    if (get_long(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 0);
        }
        return -1;
    }
    i = f->size;
    if (i != SIZEOF_LONG) {
        if ((i == 2) && (x < -32768 || x > 32767))
            RANGE_ERROR(state, f, 0);
#if (SIZEOF_LONG != 4)
        else if ((i == 4) && (x < -2147483648L || x > 2147483647L))
            RANGE_ERROR(state, f, 0);
#endif
    }
    do {
        *q++ = (unsigned char)(x & 0xffL);
        x >>= 8;
    } while (--i > 0);
    return 0;
}

static int
lp_uint(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    unsigned long x;
    Py_ssize_t i;
    unsigned char *q = (unsigned char *)p;
    if (get_ulong(state, v, &x) < 0) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            RANGE_ERROR(state, f, 1);
        }
        return -1;
    }
    i = f->size;
    if (i != SIZEOF_LONG) {
        unsigned long maxint = 1;
        maxint <<= (unsigned long)(i * 8);
        if (x >= maxint)
            RANGE_ERROR(state, f, 1);
    }
    do {
        *q++ = (unsigned char)(x & 0xffUL);
        x >>= 8;
    } while (--i > 0);
    return 0;
}

static int
lp_longlong(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    int res;
    v = get_pylong(state, v);
    if (v == NULL)
        return -1;
    res = _PyLong_AsByteArray((PyLongObject*)v,
                              (unsigned char *)p,
                              8,
                              1, /* little_endian */
                              1, /* signed */
                              0  /* !with_exceptions */);
    Py_DECREF(v);
    if (res < 0) {
        PyErr_Format(state->StructError,
                     "'%c' format requires %lld <= number <= %lld",
                     f->format,
                     LLONG_MIN,
                     LLONG_MAX);
        return -1;
    }
    return res;
}

static int
lp_ulonglong(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    int res;
    v = get_pylong(state, v);
    if (v == NULL)
        return -1;
    res = _PyLong_AsByteArray((PyLongObject*)v,
                              (unsigned char *)p,
                              8,
                              1, /* little_endian */
                              0, /* signed */
                              0  /* !with_exceptions */);
    Py_DECREF(v);
    if (res < 0) {
        PyErr_Format(state->StructError,
                     "'%c' format requires 0 <= number <= %llu",
                     f->format,
                     ULLONG_MAX);
        return -1;
    }
    return res;
}

static int
lp_halffloat(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    return pack_halffloat(state, p, v, 1);
}

static int
lp_float(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    double x = PyFloat_AsDouble(v);
    if (x == -1 && PyErr_Occurred()) {
        PyErr_SetString(state->StructError,
                        "required argument is not a float");
        return -1;
    }
    return PyFloat_Pack4(x, p, 1);
}

static int
lp_double(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
    double x = PyFloat_AsDouble(v);
    if (x == -1 && PyErr_Occurred()) {
        PyErr_SetString(state->StructError,
                        "required argument is not a float");
        return -1;
    }
    return PyFloat_Pack8(x, p, 1);
}

static formatdef lilendian_table[] = {
    {'x',       1,              0,              NULL},
    {'b',       1,              0,              nu_byte,        np_byte},
    {'B',       1,              0,              nu_ubyte,       np_ubyte},
    {'c',       1,              0,              nu_char,        np_char},
    {'s',       1,              0,              NULL},
    {'p',       1,              0,              NULL},
    {'h',       2,              0,              lu_short,       lp_int},
    {'H',       2,              0,              lu_uint,        lp_uint},
    {'i',       4,              0,              lu_int,         lp_int},
    {'I',       4,              0,              lu_uint,        lp_uint},
    {'l',       4,              0,              lu_int,         lp_int},
    {'L',       4,              0,              lu_uint,        lp_uint},
    {'q',       8,              0,              lu_longlong,    lp_longlong},
    {'Q',       8,              0,              lu_ulonglong,   lp_ulonglong},
    {'?',       1,              0,              bu_bool,        bp_bool}, /* Std rep not endian dep,
        but potentially different from native rep -- reuse bx_bool funcs. */
    {'e',       2,              0,              lu_halffloat,   lp_halffloat},
    {'f',       4,              0,              lu_float,       lp_float},
    {'d',       8,              0,              lu_double,      lp_double},
    {0}
};


static const formatdef *
whichtable(const char **pfmt)
{
    const char *fmt = (*pfmt)++; /* May be backed out of later */
    switch (*fmt) {
    case '<':
        return lilendian_table;
    case '>':
    case '!': /* Network byte order is big-endian */
        return bigendian_table;
    case '=': { /* Host byte order -- different from native in alignment! */
#if PY_LITTLE_ENDIAN
        return lilendian_table;
#else
        return bigendian_table;
#endif
    }
    default:
        --*pfmt; /* Back out of pointer increment */
        /* Fall through */
    case '@':
        return native_table;
    }
}


/* Get the table entry for a format code */

static const formatdef *
getentry(_structmodulestate *state, int c, const formatdef *f)
{
    for (; f->format != '\0'; f++) {
        if (f->format == c) {
            return f;
        }
    }
    PyErr_SetString(state->StructError, "bad char in struct format");
    return NULL;
}


/* Align a size according to a format code.  Return -1 on overflow. */

static Py_ssize_t
align(Py_ssize_t size, char c, const formatdef *e)
{
    Py_ssize_t extra;

    if (e->format == c) {
        if (e->alignment && size > 0) {
            extra = (e->alignment - 1) - (size - 1) % (e->alignment);
            if (extra > PY_SSIZE_T_MAX - size)
                return -1;
            size += extra;
        }
    }
    return size;
}

/*
 * Struct object implementation.
 */

/* calculate the size of a format string */

static int
prepare_s(PyStructObject *self, PyObject *format)
{
    const formatdef *f;
    const formatdef *e;
    formatcode *codes, *codes0;

    const char *s;
    const char *fmt;
    char c;
    Py_ssize_t size, len, num, itemsize;
    size_t ncodes;

    _structmodulestate *state = get_struct_state_structinst(self);

    fmt = PyBytes_AS_STRING(format);
    if (strlen(fmt) != (size_t)PyBytes_GET_SIZE(format)) {
        PyErr_SetString(state->StructError,
                        "embedded null character");
        return -1;
    }

    f = whichtable(&fmt);

    s = fmt;
    size = 0;
    len = 0;
    ncodes = 0;
    while ((c = *s++) != '\0') {
        if (Py_ISSPACE(c))
            continue;
        if ('0' <= c && c <= '9') {
            num = c - '0';
            while ('0' <= (c = *s++) && c <= '9') {
                /* overflow-safe version of
                   if (num*10 + (c - '0') > PY_SSIZE_T_MAX) { ... } */
                if (num >= PY_SSIZE_T_MAX / 10 && (
                        num > PY_SSIZE_T_MAX / 10 ||
                        (c - '0') > PY_SSIZE_T_MAX % 10))
                    goto overflow;
                num = num*10 + (c - '0');
            }
            if (c == '\0') {
                PyErr_SetString(state->StructError,
                                "repeat count given without format specifier");
                return -1;
            }
        }
        else
            num = 1;

        e = getentry(state, c, f);
        if (e == NULL)
            return -1;

        switch (c) {
            case 's': /* fall through */
            case 'p':
                if (len == PY_SSIZE_T_MAX) {
                    goto overflow;
                }
                len++;
                ncodes++;
                break;
            case 'x': break;
            default:
                if (num > PY_SSIZE_T_MAX - len) {
                    goto overflow;
                }
                len += num;
                if (num) {
                    ncodes++;
                }
                break;
        }

        itemsize = e->size;
        size = align(size, c, e);
        if (size == -1)
            goto overflow;

        /* if (size + num * itemsize > PY_SSIZE_T_MAX) { ... } */
        if (num > (PY_SSIZE_T_MAX - size) / itemsize)
            goto overflow;
        size += num * itemsize;
    }

    /* check for overflow */
    if ((ncodes + 1) > ((size_t)PY_SSIZE_T_MAX / sizeof(formatcode))) {
        PyErr_NoMemory();
        return -1;
    }

    codes = PyMem_Malloc((ncodes + 1) * sizeof(formatcode));
    if (codes == NULL) {
        PyErr_NoMemory();
        return -1;
    }
    codes0 = codes;
    s = fmt;
    size = 0;
    while ((c = *s++) != '\0') {
        if (Py_ISSPACE(c))
            continue;
        if ('0' <= c && c <= '9') {
            num = c - '0';
            while ('0' <= (c = *s++) && c <= '9')
                num = num*10 + (c - '0');
        }
        else
            num = 1;

        e = getentry(state, c, f);

        size = align(size, c, e);
        if (c == 's' || c == 'p') {
            codes->offset = size;
            codes->size = num;
            codes->fmtdef = e;
            codes->repeat = 1;
            codes++;
            size += num;
        } else if (c == 'x') {
            size += num;
        } else if (num) {
            codes->offset = size;
            codes->size = e->size;
            codes->fmtdef = e;
            codes->repeat = num;
            codes++;
            size += e->size * num;
        }
    }
    codes->fmtdef = NULL;
    codes->offset = size;
    codes->size = 0;
    codes->repeat = 0;

    /* Free any s_codes value left over from a previous initialization. */
    if (self->s_codes != NULL)
        PyMem_Free(self->s_codes);
    self->s_codes = codes0;
    self->s_size = size;
    self->s_len = len;
    Py_XSETREF(self->s_format, Py_NewRef(format));

    return 0;

  overflow:
    PyErr_SetString(state->StructError,
                    "total struct size too long");
    return -1;
}

static PyObject *
s_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *self;

    assert(type != NULL);
    allocfunc alloc_func = PyType_GetSlot(type, Py_tp_alloc);
    assert(alloc_func != NULL);

    self = alloc_func(type, 0);
    if (self != NULL) {
        PyStructObject *s = (PyStructObject*)self;
        s->s_format = Py_NewRef(Py_None);
        s->s_codes = NULL;
        s->s_size = -1;
        s->s_len = -1;
    }
    return self;
}

/*[clinic input]
Struct.__init__

    format: object

Create a compiled struct object.

Return a new Struct object which writes and reads binary data according to
the format string.

See help(struct) for more on format strings.
[clinic start generated code]*/

static int
Struct___init___impl(PyStructObject *self, PyObject *format)
/*[clinic end generated code: output=b8e80862444e92d0 input=192a4575a3dde802]*/
{
    int ret = 0;

    if (PyUnicode_Check(format)) {
        format = PyUnicode_AsASCIIString(format);
        if (format == NULL)
            return -1;
    }
    else {
        Py_INCREF(format);
    }

    if (!PyBytes_Check(format)) {
        Py_DECREF(format);
        PyErr_Format(PyExc_TypeError,
                     "Struct() argument 1 must be a str or bytes object, "
                     "not %.200s",
                     _PyType_Name(Py_TYPE(format)));
        return -1;
    }

    ret = prepare_s(self, format);
    Py_DECREF(format);
    return ret;
}

static int
s_clear(PyStructObject *s)
{
    Py_CLEAR(s->s_format);
    return 0;
}

static int
s_traverse(PyStructObject *s, visitproc visit, void *arg)
{
    Py_VISIT(Py_TYPE(s));
    Py_VISIT(s->s_format);
    return 0;
}

static void
s_dealloc(PyStructObject *s)
{
    PyTypeObject *tp = Py_TYPE(s);
    PyObject_GC_UnTrack(s);
    FT_CLEAR_WEAKREFS((PyObject *)s, s->weakreflist);
    if (s->s_codes != NULL) {
        PyMem_Free(s->s_codes);
    }
    Py_XDECREF(s->s_format);
    freefunc free_func = PyType_GetSlot(Py_TYPE(s), Py_tp_free);
    free_func(s);
    Py_DECREF(tp);
}

static PyObject *
s_unpack_internal(PyStructObject *soself, const char *startfrom,
                  _structmodulestate *state) {
    formatcode *code;
    Py_ssize_t i = 0;
    PyObject *result = PyTuple_New(soself->s_len);
    if (result == NULL)
        return NULL;

    for (code = soself->s_codes; code->fmtdef != NULL; code++) {
        const formatdef *e = code->fmtdef;
        const char *res = startfrom + code->offset;
        Py_ssize_t j = code->repeat;
        while (j--) {
            PyObject *v;
            if (e->format == 's') {
                v = PyBytes_FromStringAndSize(res, code->size);
            } else if (e->format == 'p') {
                Py_ssize_t n;
                if (code->size == 0) {
                    n = 0;
                }
                else {
                    n = *(unsigned char*)res;
                    if (n >= code->size) {
                        n = code->size - 1;
                    }
                }
                v = PyBytes_FromStringAndSize(res + 1, n);
            } else {
                v = e->unpack(state, res, e);
            }
            if (v == NULL)
                goto fail;
            PyTuple_SET_ITEM(result, i++, v);
            res += code->size;
        }
    }

    return result;
fail:
    Py_DECREF(result);
    return NULL;
}

#define ENSURE_STRUCT_IS_READY(self)                             \
    do {                                                         \
        if (!(self)->s_codes) {                                  \
            PyErr_SetString(PyExc_RuntimeError,                  \
                            "Struct object is not initialized"); \
            return NULL;                                         \
        }                                                        \
    } while (0);

/*[clinic input]
Struct.unpack

    buffer: Py_buffer
    /

Return a tuple containing unpacked values.

Unpack according to the format string Struct.format. The buffer's size
in bytes must be Struct.size.

See help(struct) for more on format strings.
[clinic start generated code]*/

static PyObject *
Struct_unpack_impl(PyStructObject *self, Py_buffer *buffer)
/*[clinic end generated code: output=873a24faf02e848a input=3113f8e7038b2f6c]*/
{
    _structmodulestate *state = get_struct_state_structinst(self);
    ENSURE_STRUCT_IS_READY(self);
    if (buffer->len != self->s_size) {
        PyErr_Format(state->StructError,
                     "unpack requires a buffer of %zd bytes",
                     self->s_size);
        return NULL;
    }
    return s_unpack_internal(self, buffer->buf, state);
}

/*[clinic input]
Struct.unpack_from

    buffer: Py_buffer
    offset: Py_ssize_t = 0

Return a tuple containing unpacked values.

Values are unpacked according to the format string Struct.format.

The buffer's size in bytes, starting at position offset, must be
at least Struct.size.  A negative offset counts from the end of the
buffer.

See help(struct) for more on format strings.
[clinic start generated code]*/

static PyObject *
Struct_unpack_from_impl(PyStructObject *self, Py_buffer *buffer,
                        Py_ssize_t offset)
/*[clinic end generated code: output=57fac875e0977316 input=3451f778ed8a5345]*/
{
    _structmodulestate *state = get_struct_state_structinst(self);
    ENSURE_STRUCT_IS_READY(self);

    if (offset < 0) {
        if (offset + self->s_size > 0) {
            PyErr_Format(state->StructError,
                         "not enough data to unpack %zd bytes at offset %zd",
                         self->s_size,
                         offset);
            return NULL;
        }

        if (offset + buffer->len < 0) {
            PyErr_Format(state->StructError,
                         "offset %zd out of range for %zd-byte buffer",
                         offset,
                         buffer->len);
            return NULL;
        }
        offset += buffer->len;
    }

    if ((buffer->len - offset) < self->s_size) {
        PyErr_Format(state->StructError,
                     "unpack_from requires a buffer of at least %zu bytes for "
                     "unpacking %zd bytes at offset %zd "
                     "(actual buffer size is %zd)",
                     (size_t)self->s_size + (size_t)offset,
                     self->s_size,
                     offset,
                     buffer->len);
        return NULL;
    }
    return s_unpack_internal(self, (char*)buffer->buf + offset, state);
}



/* Unpack iterator type */

typedef struct {
    PyObject_HEAD
    PyStructObject *so;
    Py_buffer buf;
    Py_ssize_t index;
} unpackiterobject;

static void
unpackiter_dealloc(unpackiterobject *self)
{
    /* bpo-31095: UnTrack is needed before calling any callbacks */
    PyTypeObject *tp = Py_TYPE(self);
    PyObject_GC_UnTrack(self);
    Py_XDECREF(self->so);
    PyBuffer_Release(&self->buf);
    PyObject_GC_Del(self);
    Py_DECREF(tp);
}

static int
unpackiter_traverse(unpackiterobject *self, visitproc visit, void *arg)
{
    Py_VISIT(Py_TYPE(self));
    Py_VISIT(self->so);
    Py_VISIT(self->buf.obj);
    return 0;
}

static PyObject *
unpackiter_len(unpackiterobject *self, PyObject *Py_UNUSED(ignored))
{
    Py_ssize_t len;
    if (self->so == NULL)
        len = 0;
    else
        len = (self->buf.len - self->index) / self->so->s_size;
    return PyLong_FromSsize_t(len);
}

static PyMethodDef unpackiter_methods[] = {
    {"__length_hint__", (PyCFunction) unpackiter_len, METH_NOARGS, NULL},
    {NULL,              NULL}           /* sentinel */
};

static PyObject *
unpackiter_iternext(unpackiterobject *self)
{
    _structmodulestate *state = get_struct_state_iterinst(self);
    PyObject *result;
    if (self->so == NULL)
        return NULL;
    if (self->index >= self->buf.len) {
        /* Iterator exhausted */
        Py_CLEAR(self->so);
        PyBuffer_Release(&self->buf);
        return NULL;
    }
    assert(self->index + self->so->s_size <= self->buf.len);
    result = s_unpack_internal(self->so,
                               (char*) self->buf.buf + self->index,
                               state);
    self->index += self->so->s_size;
    return result;
}

static PyType_Slot unpackiter_type_slots[] = {
    {Py_tp_dealloc, unpackiter_dealloc},
    {Py_tp_getattro, PyObject_GenericGetAttr},
    {Py_tp_traverse, unpackiter_traverse},
    {Py_tp_iter, PyObject_SelfIter},
    {Py_tp_iternext, unpackiter_iternext},
    {Py_tp_methods, unpackiter_methods},
    {0, 0},
};

static PyType_Spec unpackiter_type_spec = {
    "_struct.unpack_iterator",
    sizeof(unpackiterobject),
    0,
    (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
     Py_TPFLAGS_IMMUTABLETYPE | Py_TPFLAGS_DISALLOW_INSTANTIATION),
    unpackiter_type_slots
};

/*[clinic input]
Struct.iter_unpack

    buffer: object
    /

Return an iterator yielding tuples.

Tuples are unpacked from the given bytes source, like a repeated
invocation of unpack_from().

Requires that the bytes length be a multiple of the struct size.
[clinic start generated code]*/

static PyObject *
Struct_iter_unpack(PyStructObject *self, PyObject *buffer)
/*[clinic end generated code: output=172d83d0cd15dbab input=6d65b3f3107dbc99]*/
{
    _structmodulestate *state = get_struct_state_structinst(self);
    unpackiterobject *iter;
    ENSURE_STRUCT_IS_READY(self);

    if (self->s_size == 0) {
        PyErr_Format(state->StructError,
                     "cannot iteratively unpack with a struct of length 0");
        return NULL;
    }

    iter = (unpackiterobject *) PyType_GenericAlloc((PyTypeObject *)state->unpackiter_type, 0);
    if (iter == NULL)
        return NULL;

    if (PyObject_GetBuffer(buffer, &iter->buf, PyBUF_SIMPLE) < 0) {
        Py_DECREF(iter);
        return NULL;
    }
    if (iter->buf.len % self->s_size != 0) {
        PyErr_Format(state->StructError,
                     "iterative unpacking requires a buffer of "
                     "a multiple of %zd bytes",
                     self->s_size);
        Py_DECREF(iter);
        return NULL;
    }
    iter->so = (PyStructObject*)Py_NewRef(self);
    iter->index = 0;
    return (PyObject *)iter;
}


/*
 * Guts of the pack function.
 *
 * Takes a struct object, a tuple of arguments, and offset in that tuple of
 * argument for where to start processing the arguments for packing, and a
 * character buffer for writing the packed data.  The caller must ensure
 * that the buffer may contain the required length for packing the arguments.
 * 0 is returned on success, 1 is returned if there is an error.
 *
 */
static int
s_pack_internal(PyStructObject *soself, PyObject *const *args, int offset,
                char* buf, _structmodulestate *state)
{
    formatcode *code;
    /* XXX(nnorwitz): why does i need to be a local?  can we use
       the offset parameter or do we need the wider width? */
    Py_ssize_t i;

    memset(buf, '\0', soself->s_size);
    i = offset;
    for (code = soself->s_codes; code->fmtdef != NULL; code++) {
        const formatdef *e = code->fmtdef;
        char *res = buf + code->offset;
        Py_ssize_t j = code->repeat;
        while (j--) {
            PyObject *v = args[i++];
            if (e->format == 's') {
                Py_ssize_t n;
                int isstring;
                const void *p;
                isstring = PyBytes_Check(v);
                if (!isstring && !PyByteArray_Check(v)) {
                    PyErr_SetString(state->StructError,
                                    "argument for 's' must be a bytes object");
                    return -1;
                }
                if (isstring) {
                    n = PyBytes_GET_SIZE(v);
                    p = PyBytes_AS_STRING(v);
                }
                else {
                    n = PyByteArray_GET_SIZE(v);
                    p = PyByteArray_AS_STRING(v);
                }
                if (n > code->size)
                    n = code->size;
                if (n > 0)
                    memcpy(res, p, n);
            } else if (e->format == 'p') {
                Py_ssize_t n;
                int isstring;
                const void *p;
                isstring = PyBytes_Check(v);
                if (!isstring && !PyByteArray_Check(v)) {
                    PyErr_SetString(state->StructError,
                                    "argument for 'p' must be a bytes object");
                    return -1;
                }
                if (isstring) {
                    n = PyBytes_GET_SIZE(v);
                    p = PyBytes_AS_STRING(v);
                }
                else {
                    n = PyByteArray_GET_SIZE(v);
                    p = PyByteArray_AS_STRING(v);
                }
                if (code->size == 0) {
                    n = 0;
                }
                else if (n > (code->size - 1)) {
                    n = code->size - 1;
                }
                if (n > 0)
                    memcpy(res + 1, p, n);
                if (n > 255)
                    n = 255;
                *res = Py_SAFE_DOWNCAST(n, Py_ssize_t, unsigned char);
            } else {
                if (e->pack(state, res, v, e) < 0) {
                    if (PyLong_Check(v) && PyErr_ExceptionMatches(PyExc_OverflowError))
                        PyErr_SetString(state->StructError,
                                        "int too large to convert");
                    return -1;
                }
            }
            res += code->size;
        }
    }

    /* Success */
    return 0;
}


PyDoc_STRVAR(s_pack__doc__,
"S.pack(v1, v2, ...) -> bytes\n\
\n\
Return a bytes object containing values v1, v2, ... packed according\n\
to the format string S.format.  See help(struct) for more on format\n\
strings.");

static PyObject *
s_pack(PyObject *self, PyObject *const *args, Py_ssize_t nargs)
{
    char *buf;
    PyStructObject *soself;
    _structmodulestate *state = get_struct_state_structinst(self);

    /* Validate arguments. */
    soself = (PyStructObject *)self;
    ENSURE_STRUCT_IS_READY(soself);
    assert(PyStruct_Check(self, state));
    if (nargs != soself->s_len)
    {
        PyErr_Format(state->StructError,
            "pack expected %zd items for packing (got %zd)", soself->s_len, nargs);
        return NULL;
    }

    /* Allocate a new string */
    _PyBytesWriter writer;
    _PyBytesWriter_Init(&writer);
    buf = _PyBytesWriter_Alloc(&writer, soself->s_size);
    if (buf == NULL) {
        _PyBytesWriter_Dealloc(&writer);
        return NULL;
    }

    /* Call the guts */
    if ( s_pack_internal(soself, args, 0, buf, state) != 0 ) {
        _PyBytesWriter_Dealloc(&writer);
        return NULL;
    }

    return _PyBytesWriter_Finish(&writer, buf + soself->s_size);
}

PyDoc_STRVAR(s_pack_into__doc__,
"S.pack_into(buffer, offset, v1, v2, ...)\n\
\n\
Pack the values v1, v2, ... according to the format string S.format\n\
and write the packed bytes into the writable buffer buf starting at\n\
offset.  Note that the offset is a required argument.  A negative\n\
offset counts from the end of the buffer.  See help(struct) for more\n\
on format strings.");

static PyObject *
s_pack_into(PyObject *self, PyObject *const *args, Py_ssize_t nargs)
{
    PyStructObject *soself;
    Py_buffer buffer;
    Py_ssize_t offset;
    _structmodulestate *state = get_struct_state_structinst(self);

    /* Validate arguments.  +1 is for the first arg as buffer. */
    soself = (PyStructObject *)self;
    ENSURE_STRUCT_IS_READY(soself);
    assert(PyStruct_Check(self, state));
    if (nargs != (soself->s_len + 2))
    {
        if (nargs == 0) {
            PyErr_Format(state->StructError,
                        "pack_into expected buffer argument");
        }
        else if (nargs == 1) {
            PyErr_Format(state->StructError,
                        "pack_into expected offset argument");
        }
        else {
            PyErr_Format(state->StructError,
                        "pack_into expected %zd items for packing (got %zd)",
                        soself->s_len, (nargs - 2));
        }
        return NULL;
    }

    /* Extract a writable memory buffer from the first argument */
    if (!PyArg_Parse(args[0], "w*", &buffer))
        return NULL;
    assert(buffer.len >= 0);

    /* Extract the offset from the first argument */
    offset = PyNumber_AsSsize_t(args[1], PyExc_IndexError);
    if (offset == -1 && PyErr_Occurred()) {
        PyBuffer_Release(&buffer);
        return NULL;
    }

    /* Support negative offsets. */
    if (offset < 0) {
         /* Check that negative offset is low enough to fit data */
        if (offset + soself->s_size > 0) {
            PyErr_Format(state->StructError,
                         "no space to pack %zd bytes at offset %zd",
                         soself->s_size,
                         offset);
            PyBuffer_Release(&buffer);
            return NULL;
        }

        /* Check that negative offset is not crossing buffer boundary */
        if (offset + buffer.len < 0) {
            PyErr_Format(state->StructError,
                         "offset %zd out of range for %zd-byte buffer",
                         offset,
                         buffer.len);
            PyBuffer_Release(&buffer);
            return NULL;
        }

        offset += buffer.len;
    }

    /* Check boundaries */
    if ((buffer.len - offset) < soself->s_size) {
        assert(offset >= 0);
        assert(soself->s_size >= 0);

        PyErr_Format(state->StructError,
                     "pack_into requires a buffer of at least %zu bytes for "
                     "packing %zd bytes at offset %zd "
                     "(actual buffer size is %zd)",
                     (size_t)soself->s_size + (size_t)offset,
                     soself->s_size,
                     offset,
                     buffer.len);
        PyBuffer_Release(&buffer);
        return NULL;
    }

    /* Call the guts */
    if (s_pack_internal(soself, args, 2, (char*)buffer.buf + offset, state) != 0) {
        PyBuffer_Release(&buffer);
        return NULL;
    }

    PyBuffer_Release(&buffer);
    Py_RETURN_NONE;
}

static PyObject *
s_get_format(PyStructObject *self, void *unused)
{
    ENSURE_STRUCT_IS_READY(self);
    return PyUnicode_FromStringAndSize(PyBytes_AS_STRING(self->s_format),
                                       PyBytes_GET_SIZE(self->s_format));
}

static PyObject *
s_get_size(PyStructObject *self, void *unused)
{
    return PyLong_FromSsize_t(self->s_size);
}

PyDoc_STRVAR(s_sizeof__doc__,
"S.__sizeof__() -> size of S in memory, in bytes");

static PyObject *
s_sizeof(PyStructObject *self, void *unused)
{
    ENSURE_STRUCT_IS_READY(self);
    size_t size = _PyObject_SIZE(Py_TYPE(self)) + sizeof(formatcode);
    for (formatcode *code = self->s_codes; code->fmtdef != NULL; code++) {
        size += sizeof(formatcode);
    }
    return PyLong_FromSize_t(size);
}

static PyObject *
s_repr(PyStructObject *self)
{
    ENSURE_STRUCT_IS_READY(self);
    PyObject* fmt = PyUnicode_FromStringAndSize(
        PyBytes_AS_STRING(self->s_format), PyBytes_GET_SIZE(self->s_format));
    if (fmt == NULL) {
        return NULL;
    }
    PyObject* s = PyUnicode_FromFormat("%s(%R)", _PyType_Name(Py_TYPE(self)), fmt);
    Py_DECREF(fmt);
    return s;
}

/* List of functions */

static struct PyMethodDef s_methods[] = {
    STRUCT_ITER_UNPACK_METHODDEF
    {"pack",            _PyCFunction_CAST(s_pack), METH_FASTCALL, s_pack__doc__},
    {"pack_into",       _PyCFunction_CAST(s_pack_into), METH_FASTCALL, s_pack_into__doc__},
    STRUCT_UNPACK_METHODDEF
    STRUCT_UNPACK_FROM_METHODDEF
    {"__sizeof__",      (PyCFunction)s_sizeof, METH_NOARGS, s_sizeof__doc__},
    {NULL,       NULL}          /* sentinel */
};

static PyMemberDef s_members[] = {
    {"__weaklistoffset__", Py_T_PYSSIZET, offsetof(PyStructObject, weakreflist), Py_READONLY},
    {NULL}  /* sentinel */
};

static PyGetSetDef s_getsetlist[] = {
    {"format", (getter)s_get_format, (setter)NULL, PyDoc_STR("struct format string"), NULL},
    {"size", (getter)s_get_size, (setter)NULL, PyDoc_STR("struct size in bytes"), NULL},
    {NULL} /* sentinel */
};

PyDoc_STRVAR(s__doc__,
"Struct(fmt) --> compiled struct object\n"
"\n"
);

static PyType_Slot PyStructType_slots[] = {
    {Py_tp_dealloc, s_dealloc},
    {Py_tp_getattro, PyObject_GenericGetAttr},
    {Py_tp_setattro, PyObject_GenericSetAttr},
    {Py_tp_repr, s_repr},
    {Py_tp_doc, (void*)s__doc__},
    {Py_tp_traverse, s_traverse},
    {Py_tp_clear, s_clear},
    {Py_tp_methods, s_methods},
    {Py_tp_members, s_members},
    {Py_tp_getset, s_getsetlist},
    {Py_tp_init, Struct___init__},
    {Py_tp_alloc, PyType_GenericAlloc},
    {Py_tp_new, s_new},
    {Py_tp_free, PyObject_GC_Del},
    {0, 0},
};

static PyType_Spec PyStructType_spec = {
    "_struct.Struct",
    sizeof(PyStructObject),
    0,
    (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
     Py_TPFLAGS_BASETYPE | Py_TPFLAGS_IMMUTABLETYPE),
    PyStructType_slots
};


/* ---- Standalone functions  ---- */

#define MAXCACHE 100

static int
cache_struct_converter(PyObject *module, PyObject *fmt, PyStructObject **ptr)
{
    PyObject *s_object;
    PyObject *key;
    _structmodulestate *state = get_struct_state(module);

    if (fmt == NULL) {
        Py_SETREF(*ptr, NULL);
        return 1;
    }

    /* Use a str cache key: an equal str and bytes would collide and be
       compared, raising BytesWarning under -bb. */
    if (PyBytes_Check(fmt)) {
        key = PyUnicode_DecodeASCII(PyBytes_AS_STRING(fmt),
                                    PyBytes_GET_SIZE(fmt), "surrogateescape");
        if (key == NULL) {
            return 0;
        }
    }
    else {
        key = Py_NewRef(fmt);
    }

    if (PyDict_GetItemRef(state->cache, key, &s_object) < 0) {
        Py_DECREF(key);
        return 0;
    }
    if (s_object != NULL) {
        Py_DECREF(key);
        *ptr = (PyStructObject *)s_object;
        return Py_CLEANUP_SUPPORTED;
    }

    s_object = PyObject_CallOneArg(state->PyStructType, key);
    if (s_object != NULL) {
        if (PyDict_GET_SIZE(state->cache) >= MAXCACHE)
            PyDict_Clear(state->cache);
        /* Attempt to cache the result */
        if (PyDict_SetItem(state->cache, key, s_object) == -1)
            PyErr_Clear();
        Py_DECREF(key);
        *ptr = (PyStructObject *)s_object;
        return Py_CLEANUP_SUPPORTED;
    }
    Py_DECREF(key);
    return 0;
}

/*[clinic input]
_clearcache

Clear the internal cache.
[clinic start generated code]*/

static PyObject *
_clearcache_impl(PyObject *module)
/*[clinic end generated code: output=ce4fb8a7bf7cb523 input=463eaae04bab3211]*/
{
    PyDict_Clear(get_struct_state(module)->cache);
    Py_RETURN_NONE;
}


/*[clinic input]
calcsize -> Py_ssize_t

    format as s_object: cache_struct
    /

Return size in bytes of the struct described by the format string.
[clinic start generated code]*/

static Py_ssize_t
calcsize_impl(PyObject *module, PyStructObject *s_object)
/*[clinic end generated code: output=db7d23d09c6932c4 input=96a6a590c7717ecd]*/
{
    return s_object->s_size;
}

PyDoc_STRVAR(pack_doc,
"pack(format, v1, v2, ...) -> bytes\n\
\n\
Return a bytes object containing the values v1, v2, ... packed according\n\
to the format string.  See help(struct) for more on format strings.");

static PyObject *
pack(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
{
    PyObject *s_object = NULL;
    PyObject *format, *result;

    if (nargs == 0) {
        PyErr_SetString(PyExc_TypeError, "missing format argument");
        return NULL;
    }
    format = args[0];

    if (!cache_struct_converter(module, format, (PyStructObject **)&s_object)) {
        return NULL;
    }
    result = s_pack(s_object, args + 1, nargs - 1);
    Py_DECREF(s_object);
    return result;
}

PyDoc_STRVAR(pack_into_doc,
"pack_into(format, buffer, offset, v1, v2, ...)\n\
\n\
Pack the values v1, v2, ... according to the format string and write\n\
the packed bytes into the writable buffer buf starting at offset.  Note\n\
that the offset is a required argument.  A negative offset counts from\n\
the end of the buffer.  See help(struct) for more on format strings.");

static PyObject *
pack_into(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
{
    PyObject *s_object = NULL;
    PyObject *format, *result;

    if (nargs == 0) {
        PyErr_SetString(PyExc_TypeError, "missing format argument");
        return NULL;
    }
    format = args[0];

    if (!cache_struct_converter(module, format, (PyStructObject **)&s_object)) {
        return NULL;
    }
    result = s_pack_into(s_object, args + 1, nargs - 1);
    Py_DECREF(s_object);
    return result;
}

/*[clinic input]
unpack

    format as s_object: cache_struct
    buffer: Py_buffer
    /

Return a tuple containing values unpacked according to the format string.

The buffer's size in bytes must be calcsize(format).

See help(struct) for more on format strings.
[clinic start generated code]*/

static PyObject *
unpack_impl(PyObject *module, PyStructObject *s_object, Py_buffer *buffer)
/*[clinic end generated code: output=48ddd4d88eca8551 input=05fa3b91678da727]*/
{
    return Struct_unpack_impl(s_object, buffer);
}

/*[clinic input]
unpack_from

    format as s_object: cache_struct
    /
    buffer: Py_buffer
    offset: Py_ssize_t = 0

Return a tuple containing values unpacked according to the format string.

The buffer's size, minus offset, must be at least calcsize(format).
A negative offset counts from the end of the buffer.

See help(struct) for more on format strings.
[clinic start generated code]*/

static PyObject *
unpack_from_impl(PyObject *module, PyStructObject *s_object,
                 Py_buffer *buffer, Py_ssize_t offset)
/*[clinic end generated code: output=1042631674c6e0d3 input=e383ecb97728be2b]*/
{
    return Struct_unpack_from_impl(s_object, buffer, offset);
}

/*[clinic input]
iter_unpack

    format as s_object: cache_struct
    buffer: object
    /

Return an iterator yielding tuples unpacked from the given bytes.

The bytes are unpacked according to the format string, like
a repeated invocation of unpack_from().

Requires that the bytes length be a multiple of the format struct size.
[clinic start generated code]*/

static PyObject *
iter_unpack_impl(PyObject *module, PyStructObject *s_object,
                 PyObject *buffer)
/*[clinic end generated code: output=0ae50e250d20e74d input=b214a58869a3c98d]*/
{
    return Struct_iter_unpack(s_object, buffer);
}

static struct PyMethodDef module_functions[] = {
    _CLEARCACHE_METHODDEF
    CALCSIZE_METHODDEF
    ITER_UNPACK_METHODDEF
    {"pack",            _PyCFunction_CAST(pack), METH_FASTCALL,   pack_doc},
    {"pack_into",       _PyCFunction_CAST(pack_into), METH_FASTCALL,   pack_into_doc},
    UNPACK_METHODDEF
    UNPACK_FROM_METHODDEF
    {NULL,       NULL}          /* sentinel */
};


/* Module initialization */

PyDoc_STRVAR(module_doc,
"Functions to convert between Python values and C structs.\n\
Python bytes objects are used to hold the data representing the C struct.\n\
The format string (explained below) describes the layout of data\n\
in the C struct.\n\
\n\
The optional first format char indicates byte order, size and alignment:\n\
  @: native order, size & alignment (default)\n\
  =: native order, std. size & alignment\n\
  <: little-endian, std. size & alignment\n\
  >: big-endian, std. size & alignment\n\
  !: same as >\n\
\n\
The remaining characters indicate types of args and must match exactly;\n\
these can be preceded by a decimal repeat count:\n\
  x: pad byte (no data); c: char; b: signed byte; B: unsigned byte;\n\
  ?: _Bool; h: short; H: unsigned short; i: int; I: unsigned int;\n\
  l: long; L: unsigned long; q: long long; Q: unsigned long long;\n\
  f: float; d: double; e: half-float;\n\
Special cases (preceding decimal count indicates length):\n\
  s: byte string (array of char); p: Pascal string (with count byte).\n\
Special cases (only available in native format):\n\
  n: ssize_t; N: size_t;\n\
  P: an integer type that is wide enough to hold a pointer.\n\
Whitespace between formats is ignored.\n\
\n\
The variable struct.error is an exception raised on errors.\n");


static int
_structmodule_traverse(PyObject *module, visitproc visit, void *arg)
{
    _structmodulestate *state = get_struct_state(module);
    if (state) {
        Py_VISIT(state->cache);
        Py_VISIT(state->PyStructType);
        Py_VISIT(state->unpackiter_type);
        Py_VISIT(state->StructError);
    }
    return 0;
}

static int
_structmodule_clear(PyObject *module)
{
    _structmodulestate *state = get_struct_state(module);
    if (state) {
        Py_CLEAR(state->cache);
        Py_CLEAR(state->PyStructType);
        Py_CLEAR(state->unpackiter_type);
        Py_CLEAR(state->StructError);
    }
    return 0;
}

static void
_structmodule_free(void *module)
{
    _structmodule_clear((PyObject *)module);
}

static int
_structmodule_exec(PyObject *m)
{
    _structmodulestate *state = get_struct_state(m);

    state->cache = PyDict_New();
    if (state->cache == NULL) {
        return -1;
    }

    state->PyStructType = PyType_FromModuleAndSpec(
        m, &PyStructType_spec, NULL);
    if (state->PyStructType == NULL) {
        return -1;
    }
    if (PyModule_AddType(m, (PyTypeObject *)state->PyStructType) < 0) {
        return -1;
    }

    state->unpackiter_type = PyType_FromModuleAndSpec(
        m, &unpackiter_type_spec, NULL);
    if (state->unpackiter_type == NULL) {
        return -1;
    }

    /* Check endian and swap in faster functions */
    {
        const formatdef *native = native_table;
        formatdef *other, *ptr;
#if PY_LITTLE_ENDIAN
        other = lilendian_table;
#else
        other = bigendian_table;
#endif
        /* Scan through the native table, find a matching
           entry in the endian table and swap in the
           native implementations whenever possible
           (64-bit platforms may not have "standard" sizes) */
        while (native->format != '\0' && other->format != '\0') {
            ptr = other;
            while (ptr->format != '\0') {
                if (ptr->format == native->format) {
                    /* Match faster when formats are
                       listed in the same order */
                    if (ptr == other)
                        other++;
                    /* Only use the trick if the
                       size matches */
                    if (ptr->size != native->size)
                        break;
                    /* Skip float and double, could be
                       "unknown" float format */
                    if (ptr->format == 'd' || ptr->format == 'f')
                        break;
                    /* Skip _Bool, semantics are different for standard size */
                    if (ptr->format == '?')
                        break;
                    ptr->pack = native->pack;
                    ptr->unpack = native->unpack;
                    break;
                }
                ptr++;
            }
            native++;
        }
    }

    /* Add some symbolic constants to the module */
    state->StructError = PyErr_NewException("struct.error", NULL, NULL);
    if (state->StructError == NULL) {
        return -1;
    }
    if (PyModule_AddObjectRef(m, "error", state->StructError) < 0) {
        return -1;
    }

    return 0;
}

static PyModuleDef_Slot _structmodule_slots[] = {
    {Py_mod_exec, _structmodule_exec},
    {Py_mod_multiple_interpreters, Py_MOD_PER_INTERPRETER_GIL_SUPPORTED},
    {Py_mod_gil, Py_MOD_GIL_NOT_USED},
    {0, NULL}
};

static struct PyModuleDef _structmodule = {
    PyModuleDef_HEAD_INIT,
    .m_name = "_struct",
    .m_doc = module_doc,
    .m_size = sizeof(_structmodulestate),
    .m_methods = module_functions,
    .m_slots = _structmodule_slots,
    .m_traverse = _structmodule_traverse,
    .m_clear = _structmodule_clear,
    .m_free = _structmodule_free,
};

PyMODINIT_FUNC
PyInit__struct(void)
{
    return PyModuleDef_Init(&_structmodule);
}