C/Common/EfiCompress.c

/** @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 - 2014, Intel Corporation. All rights reserved.<BR>
This program and the accompanying materials
are licensed and made available under the terms and conditions of the BSD License
which accompanies this distribution.  The full text of the license may be found at
http://opensource.org/licenses/bsd-license.php

THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.

**/

#include "Compress.h"


//
// 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            (1U << 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

Argements: (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. Travese 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

Argments:

  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;
}