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205 lines
6.8 KiB
205 lines
6.8 KiB
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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 1.0.6 of 6 September 2010 |
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Copyright (C) 1996-2010 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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