BaseTools/Source/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;
}