src/util/eficompress.c - master - githubmirror/ipxe

src/util/eficompress.c
1 587 строк24 KB
Michael Brown
[efi] Compress EFI ROM images
19 фев 2021, 22:58
19 фев 2021, 22:58b76281a
/** @file
Compression routine. The compression algorithm is a mixture of LZ77 and Huffman
coding. LZ77 transforms the source data into a sequence of Original Characters
and Pointers to repeated strings. This sequence is further divided into Blocks
and Huffman codings are applied to each Block.

Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR>
SPDX-License-Identifier: BSD-2-Clause-Patent

**/

//
// Macro Definitions
//

#undef UINT8_MAX
typedef INT16             NODE;
#define UINT8_MAX         0xff
#define UINT8_BIT         8
#define THRESHOLD         3
#define INIT_CRC          0
#define WNDBIT            13
#define WNDSIZ            (1 << WNDBIT)
#define MAXMATCH          256
#define PERC_FLAG         0x8000U
#define CODE_BIT          16
#define NIL               0
#define MAX_HASH_VAL      (3 * WNDSIZ + (WNDSIZ / 512 + 1) * UINT8_MAX)
#define HASH(p, c)        ((p) + ((c) << (WNDBIT - 9)) + WNDSIZ * 2)
#define CRCPOLY           0xA001
#define UPDATE_CRC(c)     mCrc = mCrcTable[(mCrc ^ (c)) & 0xFF] ^ (mCrc >> UINT8_BIT)

//
// C: the Char&Len Set; P: the Position Set; T: the exTra Set
//

#define NC                (UINT8_MAX + MAXMATCH + 2 - THRESHOLD)
#define CBIT              9
#define NP                (WNDBIT + 1)
#define PBIT              4
#define NT                (CODE_BIT + 3)
#define TBIT              5
#if NT > NP
  #define                 NPT NT
#else
  #define                 NPT NP
#endif

//
// Function Prototypes
//

STATIC
VOID
PutDword(
  IN UINT32 Data
  );

STATIC
EFI_STATUS
AllocateMemory (
  );

STATIC
VOID
FreeMemory (
  );

STATIC
VOID
InitSlide (
  );

STATIC
NODE
Child (
  IN NODE q,
  IN UINT8 c
  );

STATIC
VOID
MakeChild (
  IN NODE q,
  IN UINT8 c,
  IN NODE r
  );

STATIC
VOID
Split (
  IN NODE Old
  );

STATIC
VOID
InsertNode (
  );

STATIC
VOID
DeleteNode (
  );

STATIC
VOID
GetNextMatch (
  );

STATIC
EFI_STATUS
Encode (
  );

STATIC
VOID
CountTFreq (
  );

STATIC
VOID
WritePTLen (
  IN INT32 n,
  IN INT32 nbit,
  IN INT32 Special
  );

STATIC
VOID
WriteCLen (
  );

STATIC
VOID
EncodeC (
  IN INT32 c
  );

STATIC
VOID
EncodeP (
  IN UINT32 p
  );

STATIC
VOID
SendBlock (
  );

STATIC
VOID
Output (
  IN UINT32 c,
  IN UINT32 p
  );

STATIC
VOID
HufEncodeStart (
  );

STATIC
VOID
HufEncodeEnd (
  );

STATIC
VOID
MakeCrcTable (
  );

STATIC
VOID
PutBits (
  IN INT32 n,
  IN UINT32 x
  );

STATIC
INT32
FreadCrc (
  OUT UINT8 *p,
  IN  INT32 n
  );

STATIC
VOID
InitPutBits (
  );

STATIC
VOID
CountLen (
  IN INT32 i
  );

STATIC
VOID
MakeLen (
  IN INT32 Root
  );

STATIC
VOID
DownHeap (
  IN INT32 i
  );

STATIC
VOID
MakeCode (
  IN  INT32 n,
  IN  UINT8 Len[],
  OUT UINT16 Code[]
  );

STATIC
INT32
MakeTree (
  IN  INT32   NParm,
  IN  UINT16  FreqParm[],
  OUT UINT8   LenParm[],
  OUT UINT16  CodeParm[]
  );


//
//  Global Variables
//

STATIC UINT8  *mSrc, *mDst, *mSrcUpperLimit, *mDstUpperLimit;

STATIC UINT8  *mLevel, *mText, *mChildCount, *mBuf, mCLen[NC], mPTLen[NPT], *mLen;
STATIC INT16  mHeap[NC + 1];
STATIC INT32  mRemainder, mMatchLen, mBitCount, mHeapSize, mN;
STATIC UINT32 mBufSiz = 0, mOutputPos, mOutputMask, mSubBitBuf, mCrc;
STATIC UINT32 mCompSize, mOrigSize;

STATIC UINT16 *mFreq, *mSortPtr, mLenCnt[17], mLeft[2 * NC - 1], mRight[2 * NC - 1],
              mCrcTable[UINT8_MAX + 1], mCFreq[2 * NC - 1],mCCode[NC],
              mPFreq[2 * NP - 1], mPTCode[NPT], mTFreq[2 * NT - 1];

STATIC NODE   mPos, mMatchPos, mAvail, *mPosition, *mParent, *mPrev, *mNext = NULL;


//
// functions
//

EFI_STATUS
EfiCompress (
  IN      UINT8   *SrcBuffer,
  IN      UINT32  SrcSize,
  IN      UINT8   *DstBuffer,
  IN OUT  UINT32  *DstSize
  )
/*++

Routine Description:

  The main compression routine.

Arguments:

  SrcBuffer   - The buffer storing the source data
  SrcSize     - The size of source data
  DstBuffer   - The buffer to store the compressed data
  DstSize     - On input, the size of DstBuffer; On output,
                the size of the actual compressed data.

Returns:

  EFI_BUFFER_TOO_SMALL  - The DstBuffer is too small. In this case,
                DstSize contains the size needed.
  EFI_SUCCESS           - Compression is successful.

--*/
{
  EFI_STATUS Status = EFI_SUCCESS;

  //
  // Initializations
  //
  mBufSiz = 0;
  mBuf = NULL;
  mText       = NULL;
  mLevel      = NULL;
  mChildCount = NULL;
  mPosition   = NULL;
  mParent     = NULL;
  mPrev       = NULL;
  mNext       = NULL;


  mSrc = SrcBuffer;
  mSrcUpperLimit = mSrc + SrcSize;
  mDst = DstBuffer;
  mDstUpperLimit = mDst + *DstSize;

  PutDword(0L);
  PutDword(0L);

  MakeCrcTable ();

  mOrigSize = mCompSize = 0;
  mCrc = INIT_CRC;

  //
  // Compress it
  //

  Status = Encode();
  if (EFI_ERROR (Status)) {
    return EFI_OUT_OF_RESOURCES;
  }

  //
  // Null terminate the compressed data
  //
  if (mDst < mDstUpperLimit) {
    *mDst++ = 0;
  }

  //
  // Fill in compressed size and original size
  //
  mDst = DstBuffer;
  PutDword(mCompSize+1);
  PutDword(mOrigSize);

  //
  // Return
  //

  if (mCompSize + 1 + 8 > *DstSize) {
    *DstSize = mCompSize + 1 + 8;
    return EFI_BUFFER_TOO_SMALL;
  } else {
    *DstSize = mCompSize + 1 + 8;
    return EFI_SUCCESS;
  }

}

STATIC
VOID
PutDword(
  IN UINT32 Data
  )
/*++

Routine Description:

  Put a dword to output stream

Arguments:

  Data    - the dword to put

Returns: (VOID)

--*/
{
  if (mDst < mDstUpperLimit) {
    *mDst++ = (UINT8)(((UINT8)(Data        )) & 0xff);
  }

  if (mDst < mDstUpperLimit) {
    *mDst++ = (UINT8)(((UINT8)(Data >> 0x08)) & 0xff);
  }

  if (mDst < mDstUpperLimit) {
    *mDst++ = (UINT8)(((UINT8)(Data >> 0x10)) & 0xff);
  }

  if (mDst < mDstUpperLimit) {
    *mDst++ = (UINT8)(((UINT8)(Data >> 0x18)) & 0xff);
  }
}

STATIC
EFI_STATUS
AllocateMemory ()
/*++

Routine Description:

  Allocate memory spaces for data structures used in compression process

Arguments: (VOID)

Returns:

  EFI_SUCCESS           - Memory is allocated successfully
  EFI_OUT_OF_RESOURCES  - Allocation fails

--*/
{
  UINT32      i;

  mText       = malloc (WNDSIZ * 2 + MAXMATCH);
  if (mText == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }
  for (i = 0 ; i < WNDSIZ * 2 + MAXMATCH; i ++) {
    mText[i] = 0;
  }

  mLevel      = malloc ((WNDSIZ + UINT8_MAX + 1) * sizeof(*mLevel));
  mChildCount = malloc ((WNDSIZ + UINT8_MAX + 1) * sizeof(*mChildCount));
  mPosition   = malloc ((WNDSIZ + UINT8_MAX + 1) * sizeof(*mPosition));
  mParent     = malloc (WNDSIZ * 2 * sizeof(*mParent));
  mPrev       = malloc (WNDSIZ * 2 * sizeof(*mPrev));
  mNext       = malloc ((MAX_HASH_VAL + 1) * sizeof(*mNext));
  if (mLevel == NULL || mChildCount == NULL || mPosition == NULL ||
    mParent == NULL || mPrev == NULL || mNext == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }

  mBufSiz = 16 * 1024U;
  while ((mBuf = malloc(mBufSiz)) == NULL) {
    mBufSiz = (mBufSiz / 10U) * 9U;
    if (mBufSiz < 4 * 1024U) {
      return EFI_OUT_OF_RESOURCES;
    }
  }
  mBuf[0] = 0;

  return EFI_SUCCESS;
}

VOID
FreeMemory ()
/*++

Routine Description:

  Called when compression is completed to free memory previously allocated.

Arguments: (VOID)

Returns: (VOID)

--*/
{
  if (mText) {
    free (mText);
  }

  if (mLevel) {
    free (mLevel);
  }

  if (mChildCount) {
    free (mChildCount);
  }

  if (mPosition) {
    free (mPosition);
  }

  if (mParent) {
    free (mParent);
  }

  if (mPrev) {
    free (mPrev);
  }

  if (mNext) {
    free (mNext);
  }

  if (mBuf) {
    free (mBuf);
  }

  return;
}


STATIC
VOID
InitSlide ()
/*++

Routine Description:

  Initialize String Info Log data structures

Arguments: (VOID)

Returns: (VOID)

--*/
{
  NODE i;

  for (i = WNDSIZ; i <= WNDSIZ + UINT8_MAX; i++) {
    mLevel[i] = 1;
    mPosition[i] = NIL;  /* sentinel */
  }
  for (i = WNDSIZ; i < WNDSIZ * 2; i++) {
    mParent[i] = NIL;
  }
  mAvail = 1;
  for (i = 1; i < WNDSIZ - 1; i++) {
    mNext[i] = (NODE)(i + 1);
  }

  mNext[WNDSIZ - 1] = NIL;
  for (i = WNDSIZ * 2; i <= MAX_HASH_VAL; i++) {
    mNext[i] = NIL;
  }
}


STATIC
NODE
Child (
  IN NODE q,
  IN UINT8 c
  )
/*++

Routine Description:

  Find child node given the parent node and the edge character

Arguments:

  q       - the parent node
  c       - the edge character

Returns:

  The child node (NIL if not found)

--*/
{
  NODE r;

  r = mNext[HASH(q, c)];
  mParent[NIL] = q;  /* sentinel */
  while (mParent[r] != q) {
    r = mNext[r];
  }

  return r;
}

STATIC
VOID
MakeChild (
  IN NODE q,
  IN UINT8 c,
  IN NODE r
  )
/*++

Routine Description:

  Create a new child for a given parent node.

Arguments:

  q       - the parent node
  c       - the edge character
  r       - the child node

Returns: (VOID)

--*/
{
  NODE h, t;

  h = (NODE)HASH(q, c);
  t = mNext[h];
  mNext[h] = r;
  mNext[r] = t;
  mPrev[t] = r;
  mPrev[r] = h;
  mParent[r] = q;
  mChildCount[q]++;
}

STATIC
VOID
Split (
  NODE Old
  )
/*++

Routine Description:

  Split a node.

Arguments:

  Old     - the node to split

Returns: (VOID)

--*/
{
  NODE New, t;

  New = mAvail;
  mAvail = mNext[New];
  mChildCount[New] = 0;
  t = mPrev[Old];
  mPrev[New] = t;
  mNext[t] = New;
  t = mNext[Old];
  mNext[New] = t;
  mPrev[t] = New;
  mParent[New] = mParent[Old];
  mLevel[New] = (UINT8)mMatchLen;
  mPosition[New] = mPos;
  MakeChild(New, mText[mMatchPos + mMatchLen], Old);
  MakeChild(New, mText[mPos + mMatchLen], mPos);
}

STATIC
VOID
InsertNode ()
/*++

Routine Description:

  Insert string info for current position into the String Info Log

Arguments: (VOID)

Returns: (VOID)

--*/
{
  NODE q, r, j, t;
  UINT8 c, *t1, *t2;

  if (mMatchLen >= 4) {

    //
    // We have just got a long match, the target tree
    // can be located by MatchPos + 1. Traverse the tree
    // from bottom up to get to a proper starting point.
    // The usage of PERC_FLAG ensures proper node deletion
    // in DeleteNode() later.
    //

    mMatchLen--;
    r = (INT16)((mMatchPos + 1) | WNDSIZ);
    while ((q = mParent[r]) == NIL) {
      r = mNext[r];
    }
    while (mLevel[q] >= mMatchLen) {
      r = q;  q = mParent[q];
    }
    t = q;
    while (mPosition[t] < 0) {
      mPosition[t] = mPos;
      t = mParent[t];
    }
    if (t < WNDSIZ) {
      mPosition[t] = (NODE)(mPos | PERC_FLAG);
    }
  } else {

    //
    // Locate the target tree
    //

    q = (INT16)(mText[mPos] + WNDSIZ);
    c = mText[mPos + 1];
    if ((r = Child(q, c)) == NIL) {
      MakeChild(q, c, mPos);
      mMatchLen = 1;
      return;
    }
    mMatchLen = 2;
  }

  //
  // Traverse down the tree to find a match.
  // Update Position value along the route.
  // Node split or creation is involved.
  //

  for ( ; ; ) {
    if (r >= WNDSIZ) {
      j = MAXMATCH;
      mMatchPos = r;
    } else {
      j = mLevel[r];
      mMatchPos = (NODE)(mPosition[r] & ~PERC_FLAG);
    }
    if (mMatchPos >= mPos) {
      mMatchPos -= WNDSIZ;
    }
    t1 = &mText[mPos + mMatchLen];
    t2 = &mText[mMatchPos + mMatchLen];
    while (mMatchLen < j) {
      if (*t1 != *t2) {
        Split(r);
        return;
      }
      mMatchLen++;
      t1++;
      t2++;
    }
    if (mMatchLen >= MAXMATCH) {
      break;
    }
    mPosition[r] = mPos;
    q = r;
    if ((r = Child(q, *t1)) == NIL) {
      MakeChild(q, *t1, mPos);
      return;
    }
    mMatchLen++;
  }
  t = mPrev[r];
  mPrev[mPos] = t;
  mNext[t] = mPos;
  t = mNext[r];
  mNext[mPos] = t;
  mPrev[t] = mPos;
  mParent[mPos] = q;
  mParent[r] = NIL;

  //
  // Special usage of 'next'
  //
  mNext[r] = mPos;

}

STATIC
VOID
DeleteNode ()
/*++

Routine Description:

  Delete outdated string info. (The Usage of PERC_FLAG
  ensures a clean deletion)

Arguments: (VOID)

Returns: (VOID)

--*/
{
  NODE q, r, s, t, u;

  if (mParent[mPos] == NIL) {
    return;
  }

  r = mPrev[mPos];
  s = mNext[mPos];
  mNext[r] = s;
  mPrev[s] = r;
  r = mParent[mPos];
  mParent[mPos] = NIL;
  if (r >= WNDSIZ || --mChildCount[r] > 1) {
    return;
  }
  t = (NODE)(mPosition[r] & ~PERC_FLAG);
  if (t >= mPos) {
    t -= WNDSIZ;
  }
  s = t;
  q = mParent[r];
  while ((u = mPosition[q]) & PERC_FLAG) {
    u &= ~PERC_FLAG;
    if (u >= mPos) {
      u -= WNDSIZ;
    }
    if (u > s) {
      s = u;
    }
    mPosition[q] = (INT16)(s | WNDSIZ);
    q = mParent[q];
  }
  if (q < WNDSIZ) {
    if (u >= mPos) {
      u -= WNDSIZ;
    }
    if (u > s) {
      s = u;
    }
    mPosition[q] = (INT16)(s | WNDSIZ | PERC_FLAG);
  }
  s = Child(r, mText[t + mLevel[r]]);
  t = mPrev[s];
  u = mNext[s];
  mNext[t] = u;
  mPrev[u] = t;
  t = mPrev[r];
  mNext[t] = s;
  mPrev[s] = t;
  t = mNext[r];
  mPrev[t] = s;
  mNext[s] = t;
  mParent[s] = mParent[r];
  mParent[r] = NIL;
  mNext[r] = mAvail;
  mAvail = r;
}

STATIC
VOID
GetNextMatch ()
/*++

Routine Description:

  Advance the current position (read in new data if needed).
  Delete outdated string info. Find a match string for current position.

Arguments: (VOID)

Returns: (VOID)

--*/
{
  INT32 n;

  mRemainder--;
  if (++mPos == WNDSIZ * 2) {
    memmove(&mText[0], &mText[WNDSIZ], WNDSIZ + MAXMATCH);
    n = FreadCrc(&mText[WNDSIZ + MAXMATCH], WNDSIZ);
    mRemainder += n;
    mPos = WNDSIZ;
  }
  DeleteNode();
  InsertNode();
}

STATIC
EFI_STATUS
Encode ()
/*++

Routine Description:

  The main controlling routine for compression process.

Arguments: (VOID)

Returns:

  EFI_SUCCESS           - The compression is successful
  EFI_OUT_0F_RESOURCES  - Not enough memory for compression process

--*/
{
  EFI_STATUS  Status;
  INT32       LastMatchLen;
  NODE        LastMatchPos;

  Status = AllocateMemory();
  if (EFI_ERROR(Status)) {
    FreeMemory();
    return Status;
  }

  InitSlide();

  HufEncodeStart();

  mRemainder = FreadCrc(&mText[WNDSIZ], WNDSIZ + MAXMATCH);

  mMatchLen = 0;
  mPos = WNDSIZ;
  InsertNode();
  if (mMatchLen > mRemainder) {
    mMatchLen = mRemainder;
  }
  while (mRemainder > 0) {
    LastMatchLen = mMatchLen;
    LastMatchPos = mMatchPos;
    GetNextMatch();
    if (mMatchLen > mRemainder) {
      mMatchLen = mRemainder;
    }

    if (mMatchLen > LastMatchLen || LastMatchLen < THRESHOLD) {

      //
      // Not enough benefits are gained by outputting a pointer,
      // so just output the original character
      //

      Output(mText[mPos - 1], 0);
    } else {

      //
      // Outputting a pointer is beneficial enough, do it.
      //

      Output(LastMatchLen + (UINT8_MAX + 1 - THRESHOLD),
             (mPos - LastMatchPos - 2) & (WNDSIZ - 1));
      while (--LastMatchLen > 0) {
        GetNextMatch();
      }
      if (mMatchLen > mRemainder) {
        mMatchLen = mRemainder;
      }
    }
  }

  HufEncodeEnd();
  FreeMemory();
  return EFI_SUCCESS;
}

STATIC
VOID
CountTFreq ()
/*++

Routine Description:

  Count the frequencies for the Extra Set

Arguments: (VOID)

Returns: (VOID)

--*/
{
  INT32 i, k, n, Count;

  for (i = 0; i < NT; i++) {
    mTFreq[i] = 0;
  }
  n = NC;
  while (n > 0 && mCLen[n - 1] == 0) {
    n--;
  }
  i = 0;
  while (i < n) {
    k = mCLen[i++];
    if (k == 0) {
      Count = 1;
      while (i < n && mCLen[i] == 0) {
        i++;
        Count++;
      }
      if (Count <= 2) {
        mTFreq[0] = (UINT16)(mTFreq[0] + Count);
      } else if (Count <= 18) {
        mTFreq[1]++;
      } else if (Count == 19) {
        mTFreq[0]++;
        mTFreq[1]++;
      } else {
        mTFreq[2]++;
      }
    } else {
      mTFreq[k + 2]++;
    }
  }
}

STATIC
VOID
WritePTLen (
  IN INT32 n,
  IN INT32 nbit,
  IN INT32 Special
  )
/*++

Routine Description:

  Outputs the code length array for the Extra Set or the Position Set.

Arguments:

  n       - the number of symbols
  nbit    - the number of bits needed to represent 'n'
  Special - the special symbol that needs to be take care of

Returns: (VOID)

--*/
{
  INT32 i, k;

  while (n > 0 && mPTLen[n - 1] == 0) {
    n--;
  }
  PutBits(nbit, n);
  i = 0;
  while (i < n) {
    k = mPTLen[i++];
    if (k <= 6) {
      PutBits(3, k);
    } else {
      PutBits(k - 3, (1U << (k - 3)) - 2);
    }
    if (i == Special) {
      while (i < 6 && mPTLen[i] == 0) {
        i++;
      }
      PutBits(2, (i - 3) & 3);
    }
  }
}

STATIC
VOID
WriteCLen ()
/*++

Routine Description:

  Outputs the code length array for Char&Length Set

Arguments: (VOID)

Returns: (VOID)

--*/
{
  INT32 i, k, n, Count;

  n = NC;
  while (n > 0 && mCLen[n - 1] == 0) {
    n--;
  }
  PutBits(CBIT, n);
  i = 0;
  while (i < n) {
    k = mCLen[i++];
    if (k == 0) {
      Count = 1;
      while (i < n && mCLen[i] == 0) {
        i++;
        Count++;
      }
      if (Count <= 2) {
        for (k = 0; k < Count; k++) {
          PutBits(mPTLen[0], mPTCode[0]);
        }
      } else if (Count <= 18) {
        PutBits(mPTLen[1], mPTCode[1]);
        PutBits(4, Count - 3);
      } else if (Count == 19) {
        PutBits(mPTLen[0], mPTCode[0]);
        PutBits(mPTLen[1], mPTCode[1]);
        PutBits(4, 15);
      } else {
        PutBits(mPTLen[2], mPTCode[2]);
        PutBits(CBIT, Count - 20);
      }
    } else {
      PutBits(mPTLen[k + 2], mPTCode[k + 2]);
    }
  }
}

STATIC
VOID
EncodeC (
  IN INT32 c
  )
{
  PutBits(mCLen[c], mCCode[c]);
}

STATIC
VOID
EncodeP (
  IN UINT32 p
  )
{
  UINT32 c, q;

  c = 0;
  q = p;
  while (q) {
    q >>= 1;
    c++;
  }
  PutBits(mPTLen[c], mPTCode[c]);
  if (c > 1) {
    PutBits(c - 1, p & (0xFFFFU >> (17 - c)));
  }
}

STATIC
VOID
SendBlock ()
/*++

Routine Description:

  Huffman code the block and output it.

Argument: (VOID)

Returns: (VOID)

--*/
{
  UINT32 i, k, Flags, Root, Pos, Size;
  Flags = 0;

  Root = MakeTree(NC, mCFreq, mCLen, mCCode);
  Size = mCFreq[Root];
  PutBits(16, Size);
  if (Root >= NC) {
    CountTFreq();
    Root = MakeTree(NT, mTFreq, mPTLen, mPTCode);
    if (Root >= NT) {
      WritePTLen(NT, TBIT, 3);
    } else {
      PutBits(TBIT, 0);
      PutBits(TBIT, Root);
    }
    WriteCLen();
  } else {
    PutBits(TBIT, 0);
    PutBits(TBIT, 0);
    PutBits(CBIT, 0);
    PutBits(CBIT, Root);
  }
  Root = MakeTree(NP, mPFreq, mPTLen, mPTCode);
  if (Root >= NP) {
    WritePTLen(NP, PBIT, -1);
  } else {
    PutBits(PBIT, 0);
    PutBits(PBIT, Root);
  }
  Pos = 0;
  for (i = 0; i < Size; i++) {
    if (i % UINT8_BIT == 0) {
      Flags = mBuf[Pos++];
    } else {
      Flags <<= 1;
    }
    if (Flags & (1U << (UINT8_BIT - 1))) {
      EncodeC(mBuf[Pos++] + (1U << UINT8_BIT));
      k = mBuf[Pos++] << UINT8_BIT;
      k += mBuf[Pos++];
      EncodeP(k);
    } else {
      EncodeC(mBuf[Pos++]);
    }
  }
  for (i = 0; i < NC; i++) {
    mCFreq[i] = 0;
  }
  for (i = 0; i < NP; i++) {
    mPFreq[i] = 0;
  }
}


STATIC
VOID
Output (
  IN UINT32 c,
  IN UINT32 p
  )
/*++

Routine Description:

  Outputs an Original Character or a Pointer

Arguments:

  c     - The original character or the 'String Length' element of a Pointer
  p     - The 'Position' field of a Pointer

Returns: (VOID)

--*/
{
  STATIC UINT32 CPos;

  if ((mOutputMask >>= 1) == 0) {
    mOutputMask = 1U << (UINT8_BIT - 1);
    if (mOutputPos >= mBufSiz - 3 * UINT8_BIT) {
      SendBlock();
      mOutputPos = 0;
    }
    CPos = mOutputPos++;
    mBuf[CPos] = 0;
  }
  mBuf[mOutputPos++] = (UINT8) c;
  mCFreq[c]++;
  if (c >= (1U << UINT8_BIT)) {
    mBuf[CPos] |= mOutputMask;
    mBuf[mOutputPos++] = (UINT8)(p >> UINT8_BIT);
    mBuf[mOutputPos++] = (UINT8) p;
    c = 0;
    while (p) {
      p >>= 1;
      c++;
    }
    mPFreq[c]++;
  }
}

STATIC
VOID
HufEncodeStart ()
{
  INT32 i;

  for (i = 0; i < NC; i++) {
    mCFreq[i] = 0;
  }
  for (i = 0; i < NP; i++) {
    mPFreq[i] = 0;
  }
  mOutputPos = mOutputMask = 0;
  InitPutBits();
  return;
}

STATIC
VOID
HufEncodeEnd ()
{
  SendBlock();

  //
  // Flush remaining bits
  //
  PutBits(UINT8_BIT - 1, 0);

  return;
}


STATIC
VOID
MakeCrcTable ()
{
  UINT32 i, j, r;

  for (i = 0; i <= UINT8_MAX; i++) {
    r = i;
    for (j = 0; j < UINT8_BIT; j++) {
      if (r & 1) {
        r = (r >> 1) ^ CRCPOLY;
      } else {
        r >>= 1;
      }
    }
    mCrcTable[i] = (UINT16)r;
  }
}

STATIC
VOID
PutBits (
  IN INT32 n,
  IN UINT32 x
  )
/*++

Routine Description:

  Outputs rightmost n bits of x

Arguments:

  n   - the rightmost n bits of the data is used
  x   - the data

Returns: (VOID)

--*/
{
  UINT8 Temp;

  if (n < mBitCount) {
    mSubBitBuf |= x << (mBitCount -= n);
  } else {

    Temp = (UINT8)(mSubBitBuf | (x >> (n -= mBitCount)));
    if (mDst < mDstUpperLimit) {
      *mDst++ = Temp;
    }
    mCompSize++;

    if (n < UINT8_BIT) {
      mSubBitBuf = x << (mBitCount = UINT8_BIT - n);
    } else {

      Temp = (UINT8)(x >> (n - UINT8_BIT));
      if (mDst < mDstUpperLimit) {
        *mDst++ = Temp;
      }
      mCompSize++;

      mSubBitBuf = x << (mBitCount = 2 * UINT8_BIT - n);
    }
  }
}

STATIC
INT32
FreadCrc (
  OUT UINT8 *p,
  IN  INT32 n
  )
/*++

Routine Description:

  Read in source data

Arguments:

  p   - the buffer to hold the data
  n   - number of bytes to read

Returns:

  number of bytes actually read

--*/
{
  INT32 i;

  for (i = 0; mSrc < mSrcUpperLimit && i < n; i++) {
    *p++ = *mSrc++;
  }
  n = i;

  p -= n;
  mOrigSize += n;
  while (--i >= 0) {
    UPDATE_CRC(*p++);
  }
  return n;
}


STATIC
VOID
InitPutBits ()
{
  mBitCount = UINT8_BIT;
  mSubBitBuf = 0;
}

STATIC
VOID
CountLen (
  IN INT32 i
  )
/*++

Routine Description:

  Count the number of each code length for a Huffman tree.

Arguments:

  i   - the top node

Returns: (VOID)

--*/
{
  STATIC INT32 Depth = 0;

  if (i < mN) {
    mLenCnt[(Depth < 16) ? Depth : 16]++;
  } else {
    Depth++;
    CountLen(mLeft [i]);
    CountLen(mRight[i]);
    Depth--;
  }
}

STATIC
VOID
MakeLen (
  IN INT32 Root
  )
/*++

Routine Description:

  Create code length array for a Huffman tree

Arguments:

  Root   - the root of the tree

--*/
{
  INT32 i, k;
  UINT32 Cum;

  for (i = 0; i <= 16; i++) {
    mLenCnt[i] = 0;
  }
  CountLen(Root);

  //
  // Adjust the length count array so that
  // no code will be generated longer than its designated length
  //

  Cum = 0;
  for (i = 16; i > 0; i--) {
    Cum += mLenCnt[i] << (16 - i);
  }
  while (Cum != (1U << 16)) {
    mLenCnt[16]--;
    for (i = 15; i > 0; i--) {
      if (mLenCnt[i] != 0) {
        mLenCnt[i]--;
        mLenCnt[i+1] += 2;
        break;
      }
    }
    Cum--;
  }
  for (i = 16; i > 0; i--) {
    k = mLenCnt[i];
    while (--k >= 0) {
      mLen[*mSortPtr++] = (UINT8)i;
    }
  }
}

STATIC
VOID
DownHeap (
  IN INT32 i
  )
{
  INT32 j, k;

  //
  // priority queue: send i-th entry down heap
  //

  k = mHeap[i];
  while ((j = 2 * i) <= mHeapSize) {
    if (j < mHeapSize && mFreq[mHeap[j]] > mFreq[mHeap[j + 1]]) {
      j++;
    }
    if (mFreq[k] <= mFreq[mHeap[j]]) {
      break;
    }
    mHeap[i] = mHeap[j];
    i = j;
  }
  mHeap[i] = (INT16)k;
}

STATIC
VOID
MakeCode (
  IN  INT32 n,
  IN  UINT8 Len[],
  OUT UINT16 Code[]
  )
/*++

Routine Description:

  Assign code to each symbol based on the code length array

Arguments:

  n     - number of symbols
  Len   - the code length array
  Code  - stores codes for each symbol

Returns: (VOID)

--*/
{
  INT32    i;
  UINT16   Start[18];

  Start[1] = 0;
  for (i = 1; i <= 16; i++) {
    Start[i + 1] = (UINT16)((Start[i] + mLenCnt[i]) << 1);
  }
  for (i = 0; i < n; i++) {
    Code[i] = Start[Len[i]]++;
  }
}

STATIC
INT32
MakeTree (
  IN  INT32   NParm,
  IN  UINT16  FreqParm[],
  OUT UINT8   LenParm[],
  OUT UINT16  CodeParm[]
  )
/*++

Routine Description:

  Generates Huffman codes given a frequency distribution of symbols

Arguments:

  NParm    - number of symbols
  FreqParm - frequency of each symbol
  LenParm  - code length for each symbol
  CodeParm - code for each symbol

Returns:

  Root of the Huffman tree.

--*/
{
  INT32 i, j, k, Avail;

  //
  // make tree, calculate len[], return root
  //

  mN = NParm;
  mFreq = FreqParm;
  mLen = LenParm;
  Avail = mN;
  mHeapSize = 0;
  mHeap[1] = 0;
  for (i = 0; i < mN; i++) {
    mLen[i] = 0;
    if (mFreq[i]) {
      mHeap[++mHeapSize] = (INT16)i;
    }
  }
  if (mHeapSize < 2) {
    CodeParm[mHeap[1]] = 0;
    return mHeap[1];
  }
  for (i = mHeapSize / 2; i >= 1; i--) {

    //
    // make priority queue
    //
    DownHeap(i);
  }
  mSortPtr = CodeParm;
  do {
    i = mHeap[1];
    if (i < mN) {
      *mSortPtr++ = (UINT16)i;
    }
    mHeap[1] = mHeap[mHeapSize--];
    DownHeap(1);
    j = mHeap[1];
    if (j < mN) {
      *mSortPtr++ = (UINT16)j;
    }
    k = Avail++;
    mFreq[k] = (UINT16)(mFreq[i] + mFreq[j]);
    mHeap[1] = (INT16)k;
    DownHeap(1);
    mLeft[k] = (UINT16)i;
    mRight[k] = (UINT16)j;
  } while (mHeapSize > 1);

  mSortPtr = CodeParm;
  MakeLen(k);
  MakeCode(NParm, LenParm, CodeParm);

  //
  // return root
  //
  return k;
}