llvm-project

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//===-- floattixf.c - Implement __floattixf -------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements __floattixf for the compiler_rt library.
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//
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//===----------------------------------------------------------------------===//
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#include "int_lib.h"
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#ifdef CRT_HAS_128BIT
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// Returns: convert a to a long double, rounding toward even.
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// Assumption: long double is a IEEE 80 bit floating point type padded to 128
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// bits ti_int is a 128 bit integral type
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// gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee
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// eeee | 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
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// mmmm mmmm mmmm
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COMPILER_RT_ABI xf_float __floattixf(ti_int a) {
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  if (a == 0)
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    return 0.0;
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  const unsigned N = sizeof(ti_int) * CHAR_BIT;
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  const ti_int s = a >> (N - 1);
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  a = (a ^ s) - s;
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  int sd = N - __clzti2(a); // number of significant digits
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  int e = sd - 1;           // exponent
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  if (sd > LDBL_MANT_DIG) {
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    //  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
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    //  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
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    //                                                12345678901234567890123456
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    //  1 = msb 1 bit
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    //  P = bit LDBL_MANT_DIG-1 bits to the right of 1
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    //  Q = bit LDBL_MANT_DIG bits to the right of 1
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    //  R = "or" of all bits to the right of Q
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    switch (sd) {
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    case LDBL_MANT_DIG + 1:
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      a <<= 1;
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      break;
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    case LDBL_MANT_DIG + 2:
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      break;
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    default:
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      a = ((tu_int)a >> (sd - (LDBL_MANT_DIG + 2))) |
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          ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG + 2) - sd))) != 0);
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    };
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    // finish:
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    a |= (a & 4) != 0; // Or P into R
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    ++a;               // round - this step may add a significant bit
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    a >>= 2;           // dump Q and R
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    // a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits
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    if (a & ((tu_int)1 << LDBL_MANT_DIG)) {
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      a >>= 1;
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      ++e;
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    }
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    // a is now rounded to LDBL_MANT_DIG bits
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  } else {
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    a <<= (LDBL_MANT_DIG - sd);
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    // a is now rounded to LDBL_MANT_DIG bits
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  }
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  xf_bits fb;
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  fb.u.high.s.low = ((su_int)s & 0x8000) | // sign
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                    (e + 16383);           // exponent
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  fb.u.low.all = (du_int)a;                // mantissa
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  return fb.f;
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}
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#endif // CRT_HAS_128BIT
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