huffman.c 6.83 KB
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/*-------------------------------------------------------------*/
/*--- Huffman coding low-level stuff                        ---*/
/*---                                             huffman.c ---*/
/*-------------------------------------------------------------*/

/* ------------------------------------------------------------------
This file is part of bzip2/libbzip2, a program and library for
lossless, block-sorting data compression.

bzip2/libbzip2 version 1.0.6 of 6 September 2010
Copyright (C) 1996-2010 Julian Seward <jseward@bzip.org>

This program is released under the terms of the license contained
------------------------------------------------------------------ */

#include "bzlib_private.h"

/*---------------------------------------------------*/
#define WEIGHTOF(zz0)  ((zz0) & 0xffffff00)
#define DEPTHOF(zz1)   ((zz1) & 0x000000ff)
#define MYMAX(zz2,zz3) ((zz2) > (zz3) ? (zz2) : (zz3))

(WEIGHTOF(zw1)+WEIGHTOF(zw2)) |                    \
(1 + MYMAX(DEPTHOF(zw1),DEPTHOF(zw2)))

#define UPHEAP(z)                                     \
{                                                     \
Int32 zz, tmp;                                     \
zz = z; tmp = heap[zz];                            \
while (weight[tmp] < weight[heap[zz >> 1]]) {      \
heap[zz] = heap[zz >> 1];                       \
zz >>= 1;                                       \
}                                                  \
heap[zz] = tmp;                                    \
}

#define DOWNHEAP(z)                                   \
{                                                     \
Int32 zz, yy, tmp;                                 \
zz = z; tmp = heap[zz];                            \
while (True) {                                     \
yy = zz << 1;                                   \
if (yy > nHeap) break;                          \
if (yy < nHeap &&                               \
weight[heap[yy+1]] < weight[heap[yy]])      \
yy++;                                        \
if (weight[tmp] < weight[heap[yy]]) break;      \
heap[zz] = heap[yy];                            \
zz = yy;                                        \
}                                                  \
heap[zz] = tmp;                                    \
}

/*---------------------------------------------------*/
void BZ2_hbMakeCodeLengths ( UChar *len,
Int32 *freq,
Int32 alphaSize,
Int32 maxLen )
{
/*--
Nodes and heap entries run from 1.  Entry 0
for both the heap and nodes is a sentinel.
--*/
Int32 nNodes, nHeap, n1, n2, i, j, k;
Bool  tooLong;

Int32 heap   [ BZ_MAX_ALPHA_SIZE + 2 ];
Int32 weight [ BZ_MAX_ALPHA_SIZE * 2 ];
Int32 parent [ BZ_MAX_ALPHA_SIZE * 2 ];

for (i = 0; i < alphaSize; i++)
weight[i+1] = (freq[i] == 0 ? 1 : freq[i]) << 8;

while (True) {

nNodes = alphaSize;
nHeap = 0;

heap[0] = 0;
weight[0] = 0;
parent[0] = -2;

for (i = 1; i <= alphaSize; i++) {
parent[i] = -1;
nHeap++;
heap[nHeap] = i;
UPHEAP(nHeap);
}

AssertH( nHeap < (BZ_MAX_ALPHA_SIZE+2), 2001 );

while (nHeap > 1) {
n1 = heap[1]; heap[1] = heap[nHeap]; nHeap--; DOWNHEAP(1);
n2 = heap[1]; heap[1] = heap[nHeap]; nHeap--; DOWNHEAP(1);
nNodes++;
parent[n1] = parent[n2] = nNodes;
parent[nNodes] = -1;
nHeap++;
heap[nHeap] = nNodes;
UPHEAP(nHeap);
}

AssertH( nNodes < (BZ_MAX_ALPHA_SIZE * 2), 2002 );

tooLong = False;
for (i = 1; i <= alphaSize; i++) {
j = 0;
k = i;
while (parent[k] >= 0) { k = parent[k]; j++; }
len[i-1] = j;
if (j > maxLen) tooLong = True;
}

if (! tooLong) break;

/* 17 Oct 04: keep-going condition for the following loop used
to be 'i < alphaSize', which missed the last element,
theoretically leading to the possibility of the compressor
looping.  However, this count-scaling step is only needed if
one of the generated Huffman code words is longer than
maxLen, which up to and including version 1.0.2 was 20 bits,
which is extremely unlikely.  In version 1.0.3 maxLen was
changed to 17 bits, which has minimal effect on compression
ratio, but does mean this scaling step is used from time to
time, enough to verify that it works.

This means that bzip2-1.0.3 and later will only produce
Huffman codes with a maximum length of 17 bits.  However, in
order to preserve backwards compatibility with bitstreams
produced by versions pre-1.0.3, the decompressor must still
handle lengths of up to 20. */

for (i = 1; i <= alphaSize; i++) {
j = weight[i] >> 8;
j = 1 + (j / 2);
weight[i] = j << 8;
}
}
}

/*---------------------------------------------------*/
void BZ2_hbAssignCodes ( Int32 *code,
UChar *length,
Int32 minLen,
Int32 maxLen,
Int32 alphaSize )
{
Int32 n, vec, i;

vec = 0;
for (n = minLen; n <= maxLen; n++) {
for (i = 0; i < alphaSize; i++)
if (length[i] == n) { code[i] = vec; vec++; };
vec <<= 1;
}
}

/*---------------------------------------------------*/
void BZ2_hbCreateDecodeTables ( Int32 *limit,
Int32 *base,
Int32 *perm,
UChar *length,
Int32 minLen,
Int32 maxLen,
Int32 alphaSize )
{
Int32 pp, i, j, vec;

pp = 0;
for (i = minLen; i <= maxLen; i++)
for (j = 0; j < alphaSize; j++)
if (length[j] == i) { perm[pp] = j; pp++; };

for (i = 0; i < BZ_MAX_CODE_LEN; i++) base[i] = 0;
for (i = 0; i < alphaSize; i++) base[length[i]+1]++;

for (i = 1; i < BZ_MAX_CODE_LEN; i++) base[i] += base[i-1];

for (i = 0; i < BZ_MAX_CODE_LEN; i++) limit[i] = 0;
vec = 0;

for (i = minLen; i <= maxLen; i++) {
vec += (base[i+1] - base[i]);
limit[i] = vec-1;
vec <<= 1;
}
for (i = minLen + 1; i <= maxLen; i++)
base[i] = ((limit[i-1] + 1) << 1) - base[i];
}

/*-------------------------------------------------------------*/
/*--- end                                         huffman.c ---*/
/*-------------------------------------------------------------*/``````