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loizides |
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/*-------------------------------------------------------------*/
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/*--- Huffman coding low-level stuff ---*/
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/*--- huffman.c ---*/
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/*-------------------------------------------------------------*/
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/* ------------------------------------------------------------------
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This file is part of bzip2/libbzip2, a program and library for
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lossless, block-sorting data compression.
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bzip2/libbzip2 version 1.0.5 of 10 December 2007
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Copyright (C) 1996-2007 Julian Seward <jseward@bzip.org>
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Please read the WARNING, DISCLAIMER and PATENTS sections in the
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README file.
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This program is released under the terms of the license contained
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in the file LICENSE.
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------------------------------------------------------------------ */
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#include "bzlib_private.h"
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/*---------------------------------------------------*/
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#define WEIGHTOF(zz0) ((zz0) & 0xffffff00)
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#define DEPTHOF(zz1) ((zz1) & 0x000000ff)
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#define MYMAX(zz2,zz3) ((zz2) > (zz3) ? (zz2) : (zz3))
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#define ADDWEIGHTS(zw1,zw2) \
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(WEIGHTOF(zw1)+WEIGHTOF(zw2)) | \
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(1 + MYMAX(DEPTHOF(zw1),DEPTHOF(zw2)))
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#define UPHEAP(z) \
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{ \
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Int32 zz, tmp; \
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zz = z; tmp = heap[zz]; \
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while (weight[tmp] < weight[heap[zz >> 1]]) { \
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heap[zz] = heap[zz >> 1]; \
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zz >>= 1; \
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} \
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heap[zz] = tmp; \
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}
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#define DOWNHEAP(z) \
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{ \
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Int32 zz, yy, tmp; \
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zz = z; tmp = heap[zz]; \
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while (True) { \
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yy = zz << 1; \
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if (yy > nHeap) break; \
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if (yy < nHeap && \
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weight[heap[yy+1]] < weight[heap[yy]]) \
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yy++; \
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if (weight[tmp] < weight[heap[yy]]) break; \
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heap[zz] = heap[yy]; \
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zz = yy; \
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} \
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heap[zz] = tmp; \
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}
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/*---------------------------------------------------*/
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void BZ2_hbMakeCodeLengths ( UChar *len,
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Int32 *freq,
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Int32 alphaSize,
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Int32 maxLen )
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{
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/*--
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Nodes and heap entries run from 1. Entry 0
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for both the heap and nodes is a sentinel.
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--*/
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Int32 nNodes, nHeap, n1, n2, i, j, k;
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Bool tooLong;
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Int32 heap [ BZ_MAX_ALPHA_SIZE + 2 ];
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Int32 weight [ BZ_MAX_ALPHA_SIZE * 2 ];
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Int32 parent [ BZ_MAX_ALPHA_SIZE * 2 ];
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for (i = 0; i < alphaSize; i++)
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weight[i+1] = (freq[i] == 0 ? 1 : freq[i]) << 8;
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while (True) {
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nNodes = alphaSize;
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nHeap = 0;
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heap[0] = 0;
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weight[0] = 0;
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parent[0] = -2;
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for (i = 1; i <= alphaSize; i++) {
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parent[i] = -1;
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nHeap++;
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heap[nHeap] = i;
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UPHEAP(nHeap);
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}
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AssertH( nHeap < (BZ_MAX_ALPHA_SIZE+2), 2001 );
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while (nHeap > 1) {
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n1 = heap[1]; heap[1] = heap[nHeap]; nHeap--; DOWNHEAP(1);
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n2 = heap[1]; heap[1] = heap[nHeap]; nHeap--; DOWNHEAP(1);
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nNodes++;
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parent[n1] = parent[n2] = nNodes;
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weight[nNodes] = ADDWEIGHTS(weight[n1], weight[n2]);
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parent[nNodes] = -1;
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nHeap++;
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heap[nHeap] = nNodes;
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UPHEAP(nHeap);
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}
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AssertH( nNodes < (BZ_MAX_ALPHA_SIZE * 2), 2002 );
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tooLong = False;
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for (i = 1; i <= alphaSize; i++) {
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j = 0;
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k = i;
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while (parent[k] >= 0) { k = parent[k]; j++; }
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len[i-1] = j;
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if (j > maxLen) tooLong = True;
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}
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if (! tooLong) break;
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/* 17 Oct 04: keep-going condition for the following loop used
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to be 'i < alphaSize', which missed the last element,
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theoretically leading to the possibility of the compressor
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looping. However, this count-scaling step is only needed if
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one of the generated Huffman code words is longer than
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maxLen, which up to and including version 1.0.2 was 20 bits,
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which is extremely unlikely. In version 1.0.3 maxLen was
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changed to 17 bits, which has minimal effect on compression
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ratio, but does mean this scaling step is used from time to
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time, enough to verify that it works.
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This means that bzip2-1.0.3 and later will only produce
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Huffman codes with a maximum length of 17 bits. However, in
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order to preserve backwards compatibility with bitstreams
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produced by versions pre-1.0.3, the decompressor must still
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handle lengths of up to 20. */
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for (i = 1; i <= alphaSize; i++) {
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j = weight[i] >> 8;
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j = 1 + (j / 2);
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weight[i] = j << 8;
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}
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}
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}
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/*---------------------------------------------------*/
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void BZ2_hbAssignCodes ( Int32 *code,
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UChar *length,
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Int32 minLen,
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Int32 maxLen,
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Int32 alphaSize )
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{
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Int32 n, vec, i;
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vec = 0;
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for (n = minLen; n <= maxLen; n++) {
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for (i = 0; i < alphaSize; i++)
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if (length[i] == n) { code[i] = vec; vec++; };
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vec <<= 1;
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}
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}
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/*---------------------------------------------------*/
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void BZ2_hbCreateDecodeTables ( Int32 *limit,
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Int32 *base,
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Int32 *perm,
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UChar *length,
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Int32 minLen,
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Int32 maxLen,
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Int32 alphaSize )
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{
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Int32 pp, i, j, vec;
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pp = 0;
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for (i = minLen; i <= maxLen; i++)
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for (j = 0; j < alphaSize; j++)
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if (length[j] == i) { perm[pp] = j; pp++; };
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for (i = 0; i < BZ_MAX_CODE_LEN; i++) base[i] = 0;
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for (i = 0; i < alphaSize; i++) base[length[i]+1]++;
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for (i = 1; i < BZ_MAX_CODE_LEN; i++) base[i] += base[i-1];
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for (i = 0; i < BZ_MAX_CODE_LEN; i++) limit[i] = 0;
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vec = 0;
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for (i = minLen; i <= maxLen; i++) {
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vec += (base[i+1] - base[i]);
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limit[i] = vec-1;
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vec <<= 1;
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}
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for (i = minLen + 1; i <= maxLen; i++)
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base[i] = ((limit[i-1] + 1) << 1) - base[i];
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}
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/*-------------------------------------------------------------*/
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/*--- end huffman.c ---*/
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/*-------------------------------------------------------------*/
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