1 | /* blast.c |
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2 | * Copyright (C) 2003 Mark Adler |
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3 | * For conditions of distribution and use, see copyright notice in blast.h |
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4 | * version 1.1, 16 Feb 2003 |
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5 | * |
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6 | * blast.c decompresses data compressed by the PKWare Compression Library. |
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7 | * This function provides functionality similar to the explode() function of |
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8 | * the PKWare library, hence the name "blast". |
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9 | * |
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10 | * This decompressor is based on the excellent format description provided by |
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11 | * Ben Rudiak-Gould in comp.compression on August 13, 2001. Interestingly, the |
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12 | * example Ben provided in the post is incorrect. The distance 110001 should |
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13 | * instead be 111000. When corrected, the example byte stream becomes: |
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14 | * |
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15 | * 00 04 82 24 25 8f 80 7f |
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16 | * |
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17 | * which decompresses to "AIAIAIAIAIAIA" (without the quotes). |
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18 | */ |
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19 | |
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20 | /* |
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21 | * Change history: |
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22 | * |
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23 | * 1.0 12 Feb 2003 - First version |
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24 | * 1.1 16 Feb 2003 - Fixed distance check for > 4 GB uncompressed data |
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25 | */ |
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26 | |
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27 | #include <setjmp.h> /* for setjmp(), longjmp(), and jmp_buf */ |
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28 | #include "blast.h" /* prototype for blast() */ |
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29 | |
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30 | #define local static /* for local function definitions */ |
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31 | #define MAXBITS 13 /* maximum code length */ |
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32 | #define MAXWIN 4096 /* maximum window size */ |
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33 | |
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34 | /* input and output state */ |
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35 | struct state { |
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36 | /* input state */ |
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37 | blast_in infun; /* input function provided by user */ |
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38 | void *inhow; /* opaque information passed to infun() */ |
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39 | unsigned char *in; /* next input location */ |
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40 | unsigned left; /* available input at in */ |
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41 | int bitbuf; /* bit buffer */ |
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42 | int bitcnt; /* number of bits in bit buffer */ |
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43 | |
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44 | /* input limit error return state for bits() and decode() */ |
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45 | jmp_buf env; |
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46 | |
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47 | /* output state */ |
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48 | blast_out outfun; /* output function provided by user */ |
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49 | void *outhow; /* opaque information passed to outfun() */ |
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50 | unsigned next; /* index of next write location in out[] */ |
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51 | int first; /* true to check distances (for first 4K) */ |
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52 | unsigned char out[MAXWIN]; /* output buffer and sliding window */ |
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53 | }; |
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54 | |
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55 | /* |
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56 | * Return need bits from the input stream. This always leaves less than |
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57 | * eight bits in the buffer. bits() works properly for need == 0. |
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58 | * |
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59 | * Format notes: |
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60 | * |
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61 | * - Bits are stored in bytes from the least significant bit to the most |
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62 | * significant bit. Therefore bits are dropped from the bottom of the bit |
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63 | * buffer, using shift right, and new bytes are appended to the top of the |
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64 | * bit buffer, using shift left. |
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65 | */ |
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66 | local int bits(struct state *s, int need) |
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67 | { |
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68 | int val; /* bit accumulator */ |
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69 | |
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70 | /* load at least need bits into val */ |
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71 | val = s->bitbuf; |
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72 | while (s->bitcnt < need) { |
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73 | if (s->left == 0) { |
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74 | s->left = s->infun(s->inhow, &(s->in)); |
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75 | if (s->left == 0) longjmp(s->env, 1); /* out of input */ |
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76 | } |
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77 | val |= (int)(*(s->in)++) << s->bitcnt; /* load eight bits */ |
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78 | s->left--; |
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79 | s->bitcnt += 8; |
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80 | } |
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81 | |
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82 | /* drop need bits and update buffer, always zero to seven bits left */ |
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83 | s->bitbuf = val >> need; |
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84 | s->bitcnt -= need; |
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85 | |
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86 | /* return need bits, zeroing the bits above that */ |
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87 | return val & ((1 << need) - 1); |
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88 | } |
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89 | |
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90 | /* |
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91 | * Huffman code decoding tables. count[1..MAXBITS] is the number of symbols of |
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92 | * each length, which for a canonical code are stepped through in order. |
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93 | * symbol[] are the symbol values in canonical order, where the number of |
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94 | * entries is the sum of the counts in count[]. The decoding process can be |
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95 | * seen in the function decode() below. |
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96 | */ |
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97 | struct huffman { |
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98 | short *count; /* number of symbols of each length */ |
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99 | short *symbol; /* canonically ordered symbols */ |
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100 | }; |
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101 | |
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102 | /* |
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103 | * Decode a code from the stream s using huffman table h. Return the symbol or |
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104 | * a negative value if there is an error. If all of the lengths are zero, i.e. |
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105 | * an empty code, or if the code is incomplete and an invalid code is received, |
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106 | * then -9 is returned after reading MAXBITS bits. |
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107 | * |
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108 | * Format notes: |
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109 | * |
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110 | * - The codes as stored in the compressed data are bit-reversed relative to |
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111 | * a simple integer ordering of codes of the same lengths. Hence below the |
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112 | * bits are pulled from the compressed data one at a time and used to |
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113 | * build the code value reversed from what is in the stream in order to |
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114 | * permit simple integer comparisons for decoding. |
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115 | * |
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116 | * - The first code for the shortest length is all ones. Subsequent codes of |
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117 | * the same length are simply integer decrements of the previous code. When |
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118 | * moving up a length, a one bit is appended to the code. For a complete |
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119 | * code, the last code of the longest length will be all zeros. To support |
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120 | * this ordering, the bits pulled during decoding are inverted to apply the |
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121 | * more "natural" ordering starting with all zeros and incrementing. |
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122 | */ |
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123 | local int decode(struct state *s, struct huffman *h) |
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124 | { |
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125 | int len; /* current number of bits in code */ |
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126 | int code; /* len bits being decoded */ |
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127 | int first; /* first code of length len */ |
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128 | int count; /* number of codes of length len */ |
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129 | int index; /* index of first code of length len in symbol table */ |
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130 | int bitbuf; /* bits from stream */ |
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131 | int left; /* bits left in next or left to process */ |
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132 | short *next; /* next number of codes */ |
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133 | |
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134 | bitbuf = s->bitbuf; |
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135 | left = s->bitcnt; |
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136 | code = first = index = 0; |
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137 | len = 1; |
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138 | next = h->count + 1; |
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139 | while (1) { |
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140 | while (left--) { |
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141 | code |= (bitbuf & 1) ^ 1; /* invert code */ |
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142 | bitbuf >>= 1; |
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143 | count = *next++; |
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144 | if (code < first + count) { /* if length len, return symbol */ |
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145 | s->bitbuf = bitbuf; |
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146 | s->bitcnt = (s->bitcnt - len) & 7; |
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147 | return h->symbol[index + (code - first)]; |
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148 | } |
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149 | index += count; /* else update for next length */ |
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150 | first += count; |
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151 | first <<= 1; |
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152 | code <<= 1; |
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153 | len++; |
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154 | } |
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155 | left = (MAXBITS+1) - len; |
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156 | if (left == 0) break; |
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157 | if (s->left == 0) { |
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158 | s->left = s->infun(s->inhow, &(s->in)); |
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159 | if (s->left == 0) longjmp(s->env, 1); /* out of input */ |
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160 | } |
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161 | bitbuf = *(s->in)++; |
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162 | s->left--; |
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163 | if (left > 8) left = 8; |
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164 | } |
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165 | return -9; /* ran out of codes */ |
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166 | } |
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167 | |
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168 | /* |
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169 | * Given a list of repeated code lengths rep[0..n-1], where each byte is a |
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170 | * count (high four bits + 1) and a code length (low four bits), generate the |
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171 | * list of code lengths. This compaction reduces the size of the object code. |
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172 | * Then given the list of code lengths length[0..n-1] representing a canonical |
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173 | * Huffman code for n symbols, construct the tables required to decode those |
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174 | * codes. Those tables are the number of codes of each length, and the symbols |
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175 | * sorted by length, retaining their original order within each length. The |
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176 | * return value is zero for a complete code set, negative for an over- |
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177 | * subscribed code set, and positive for an incomplete code set. The tables |
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178 | * can be used if the return value is zero or positive, but they cannot be used |
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179 | * if the return value is negative. If the return value is zero, it is not |
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180 | * possible for decode() using that table to return an error--any stream of |
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181 | * enough bits will resolve to a symbol. If the return value is positive, then |
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182 | * it is possible for decode() using that table to return an error for received |
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183 | * codes past the end of the incomplete lengths. |
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184 | */ |
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185 | local int construct(struct huffman *h, const unsigned char *rep, int n) |
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186 | { |
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187 | int symbol; /* current symbol when stepping through length[] */ |
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188 | int len; /* current length when stepping through h->count[] */ |
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189 | int left; /* number of possible codes left of current length */ |
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190 | short offs[MAXBITS+1]; /* offsets in symbol table for each length */ |
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191 | short length[256]; /* code lengths */ |
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192 | |
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193 | /* convert compact repeat counts into symbol bit length list */ |
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194 | symbol = 0; |
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195 | do { |
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196 | len = *rep++; |
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197 | left = (len >> 4) + 1; |
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198 | len &= 15; |
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199 | do { |
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200 | length[symbol++] = len; |
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201 | } while (--left); |
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202 | } while (--n); |
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203 | n = symbol; |
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204 | |
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205 | /* count number of codes of each length */ |
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206 | for (len = 0; len <= MAXBITS; len++) |
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207 | h->count[len] = 0; |
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208 | for (symbol = 0; symbol < n; symbol++) |
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209 | (h->count[length[symbol]])++; /* assumes lengths are within bounds */ |
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210 | if (h->count[0] == n) /* no codes! */ |
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211 | return 0; /* complete, but decode() will fail */ |
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212 | |
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213 | /* check for an over-subscribed or incomplete set of lengths */ |
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214 | left = 1; /* one possible code of zero length */ |
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215 | for (len = 1; len <= MAXBITS; len++) { |
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216 | left <<= 1; /* one more bit, double codes left */ |
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217 | left -= h->count[len]; /* deduct count from possible codes */ |
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218 | if (left < 0) return left; /* over-subscribed--return negative */ |
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219 | } /* left > 0 means incomplete */ |
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220 | |
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221 | /* generate offsets into symbol table for each length for sorting */ |
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222 | offs[1] = 0; |
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223 | for (len = 1; len < MAXBITS; len++) |
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224 | offs[len + 1] = offs[len] + h->count[len]; |
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225 | |
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226 | /* |
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227 | * put symbols in table sorted by length, by symbol order within each |
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228 | * length |
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229 | */ |
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230 | for (symbol = 0; symbol < n; symbol++) |
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231 | if (length[symbol] != 0) |
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232 | h->symbol[offs[length[symbol]]++] = symbol; |
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233 | |
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234 | /* return zero for complete set, positive for incomplete set */ |
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235 | return left; |
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236 | } |
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237 | |
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238 | /* |
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239 | * Decode PKWare Compression Library stream. |
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240 | * |
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241 | * Format notes: |
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242 | * |
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243 | * - First byte is 0 if literals are uncoded or 1 if they are coded. Second |
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244 | * byte is 4, 5, or 6 for the number of extra bits in the distance code. |
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245 | * This is the base-2 logarithm of the dictionary size minus six. |
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246 | * |
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247 | * - Compressed data is a combination of literals and length/distance pairs |
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248 | * terminated by an end code. Literals are either Huffman coded or |
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249 | * uncoded bytes. A length/distance pair is a coded length followed by a |
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250 | * coded distance to represent a string that occurs earlier in the |
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251 | * uncompressed data that occurs again at the current location. |
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252 | * |
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253 | * - A bit preceding a literal or length/distance pair indicates which comes |
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254 | * next, 0 for literals, 1 for length/distance. |
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255 | * |
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256 | * - If literals are uncoded, then the next eight bits are the literal, in the |
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257 | * normal bit order in th stream, i.e. no bit-reversal is needed. Similarly, |
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258 | * no bit reversal is needed for either the length extra bits or the distance |
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259 | * extra bits. |
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260 | * |
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261 | * - Literal bytes are simply written to the output. A length/distance pair is |
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262 | * an instruction to copy previously uncompressed bytes to the output. The |
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263 | * copy is from distance bytes back in the output stream, copying for length |
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264 | * bytes. |
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265 | * |
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266 | * - Distances pointing before the beginning of the output data are not |
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267 | * permitted. |
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268 | * |
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269 | * - Overlapped copies, where the length is greater than the distance, are |
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270 | * allowed and common. For example, a distance of one and a length of 518 |
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271 | * simply copies the last byte 518 times. A distance of four and a length of |
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272 | * twelve copies the last four bytes three times. A simple forward copy |
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273 | * ignoring whether the length is greater than the distance or not implements |
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274 | * this correctly. |
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275 | */ |
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276 | local int decomp(struct state *s) |
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277 | { |
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278 | int lit; /* true if literals are coded */ |
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279 | int dict; /* log2(dictionary size) - 6 */ |
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280 | int symbol; /* decoded symbol, extra bits for distance */ |
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281 | int len; /* length for copy */ |
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282 | int dist; /* distance for copy */ |
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283 | int copy; /* copy counter */ |
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284 | unsigned char *from, *to; /* copy pointers */ |
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285 | static int virgin = 1; /* build tables once */ |
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286 | static short litcnt[MAXBITS+1], litsym[256]; /* litcode memory */ |
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287 | static short lencnt[MAXBITS+1], lensym[16]; /* lencode memory */ |
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288 | static short distcnt[MAXBITS+1], distsym[64]; /* distcode memory */ |
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289 | static struct huffman litcode = {litcnt, litsym}; /* length code */ |
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290 | static struct huffman lencode = {lencnt, lensym}; /* length code */ |
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291 | static struct huffman distcode = {distcnt, distsym};/* distance code */ |
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292 | /* bit lengths of literal codes */ |
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293 | static const unsigned char litlen[] = { |
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294 | 11, 124, 8, 7, 28, 7, 188, 13, 76, 4, 10, 8, 12, 10, 12, 10, 8, 23, 8, |
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295 | 9, 7, 6, 7, 8, 7, 6, 55, 8, 23, 24, 12, 11, 7, 9, 11, 12, 6, 7, 22, 5, |
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296 | 7, 24, 6, 11, 9, 6, 7, 22, 7, 11, 38, 7, 9, 8, 25, 11, 8, 11, 9, 12, |
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297 | 8, 12, 5, 38, 5, 38, 5, 11, 7, 5, 6, 21, 6, 10, 53, 8, 7, 24, 10, 27, |
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298 | 44, 253, 253, 253, 252, 252, 252, 13, 12, 45, 12, 45, 12, 61, 12, 45, |
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299 | 44, 173}; |
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300 | /* bit lengths of length codes 0..15 */ |
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301 | static const unsigned char lenlen[] = {2, 35, 36, 53, 38, 23}; |
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302 | /* bit lengths of distance codes 0..63 */ |
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303 | static const unsigned char distlen[] = {2, 20, 53, 230, 247, 151, 248}; |
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304 | static const short base[16] = { /* base for length codes */ |
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305 | 3, 2, 4, 5, 6, 7, 8, 9, 10, 12, 16, 24, 40, 72, 136, 264}; |
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306 | static const char extra[16] = { /* extra bits for length codes */ |
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307 | 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8}; |
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308 | |
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309 | /* set up decoding tables (once--might not be thread-safe) */ |
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310 | if (virgin) { |
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311 | construct(&litcode, litlen, sizeof(litlen)); |
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312 | construct(&lencode, lenlen, sizeof(lenlen)); |
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313 | construct(&distcode, distlen, sizeof(distlen)); |
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314 | virgin = 0; |
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315 | } |
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316 | |
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317 | /* read header */ |
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318 | lit = bits(s, 8); |
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319 | if (lit > 1) return -1; |
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320 | dict = bits(s, 8); |
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321 | if (dict < 4 || dict > 6) return -2; |
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322 | |
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323 | /* decode literals and length/distance pairs */ |
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324 | do { |
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325 | if (bits(s, 1)) { |
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326 | /* get length */ |
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327 | symbol = decode(s, &lencode); |
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328 | len = base[symbol] + bits(s, extra[symbol]); |
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329 | if (len == 519) break; /* end code */ |
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330 | |
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331 | /* get distance */ |
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332 | symbol = len == 2 ? 2 : dict; |
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333 | dist = decode(s, &distcode) << symbol; |
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334 | dist += bits(s, symbol); |
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335 | dist++; |
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336 | if (s->first && dist > s->next) |
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337 | return -3; /* distance too far back */ |
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338 | |
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339 | /* copy length bytes from distance bytes back */ |
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340 | do { |
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341 | to = s->out + s->next; |
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342 | from = to - dist; |
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343 | copy = MAXWIN; |
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344 | if (s->next < dist) { |
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345 | from += copy; |
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346 | copy = dist; |
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347 | } |
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348 | copy -= s->next; |
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349 | if (copy > len) copy = len; |
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350 | len -= copy; |
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351 | s->next += copy; |
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352 | do { |
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353 | *to++ = *from++; |
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354 | } while (--copy); |
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355 | if (s->next == MAXWIN) { |
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356 | if (s->outfun(s->outhow, s->out, s->next)) return 1; |
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357 | s->next = 0; |
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358 | s->first = 0; |
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359 | } |
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360 | } while (len != 0); |
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361 | } |
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362 | else { |
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363 | /* get literal and write it */ |
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364 | symbol = lit ? decode(s, &litcode) : bits(s, 8); |
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365 | s->out[s->next++] = symbol; |
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366 | if (s->next == MAXWIN) { |
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367 | if (s->outfun(s->outhow, s->out, s->next)) return 1; |
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368 | s->next = 0; |
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369 | s->first = 0; |
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370 | } |
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371 | } |
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372 | } while (1); |
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373 | return 0; |
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374 | } |
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375 | |
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376 | /* See comments in blast.h */ |
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377 | int blast(blast_in infun, void *inhow, blast_out outfun, void *outhow) |
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378 | { |
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379 | struct state s; /* input/output state */ |
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380 | int err; /* return value */ |
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381 | |
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382 | /* initialize input state */ |
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383 | s.infun = infun; |
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384 | s.inhow = inhow; |
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385 | s.left = 0; |
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386 | s.bitbuf = 0; |
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387 | s.bitcnt = 0; |
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388 | |
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389 | /* initialize output state */ |
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390 | s.outfun = outfun; |
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391 | s.outhow = outhow; |
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392 | s.next = 0; |
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393 | s.first = 1; |
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394 | |
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395 | /* return if bits() or decode() tries to read past available input */ |
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396 | if (setjmp(s.env) != 0) /* if came back here via longjmp(), */ |
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397 | err = 2; /* then skip decomp(), return error */ |
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398 | else |
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399 | err = decomp(&s); /* decompress */ |
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400 | |
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401 | /* write any leftover output and update the error code if needed */ |
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402 | if (err != 1 && s.next && s.outfun(s.outhow, s.out, s.next) && err == 0) |
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403 | err = 1; |
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404 | return err; |
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405 | } |
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406 | |
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407 | #ifdef TEST |
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408 | /* Example of how to use blast() */ |
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409 | #include <stdio.h> |
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410 | #include <stdlib.h> |
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411 | |
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412 | #define CHUNK 16384 |
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413 | |
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414 | local unsigned inf(void *how, unsigned char **buf) |
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415 | { |
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416 | static unsigned char hold[CHUNK]; |
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417 | |
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418 | *buf = hold; |
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419 | return fread(hold, 1, CHUNK, (FILE *)how); |
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420 | } |
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421 | |
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422 | local int outf(void *how, unsigned char *buf, unsigned len) |
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423 | { |
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424 | return fwrite(buf, 1, len, (FILE *)how) != len; |
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425 | } |
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426 | |
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427 | /* Decompress a PKWare Compression Library stream from stdin to stdout */ |
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428 | int main(void) |
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429 | { |
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430 | int ret, n; |
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431 | |
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432 | /* decompress to stdout */ |
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433 | ret = blast(inf, stdin, outf, stdout); |
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434 | if (ret != 0) fprintf(stderr, "blast error: %d\n", ret); |
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435 | |
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436 | /* see if there are any leftover bytes */ |
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437 | n = 0; |
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438 | while (getchar() != EOF) n++; |
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439 | if (n) fprintf(stderr, "blast warning: %d unused bytes of input\n", n); |
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440 | |
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441 | /* return blast() error code */ |
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442 | return ret; |
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443 | } |
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444 | #endif |
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