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1 /* inftrees.c -- generate Huffman trees for efficient decoding |
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2 * Copyright (C) 1995-2005 Mark Adler |
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3 * For conditions of distribution and use, see copyright notice in zlib.h |
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4 */ |
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5 |
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6 #include "zutil.h" |
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7 #include "inftrees.h" |
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8 |
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9 #define MAXBITS 15 |
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10 |
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11 const char inflate_copyright[] = |
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12 " inflate 1.2.3 Copyright 1995-2005 Mark Adler "; |
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13 /* |
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14 If you use the zlib library in a product, an acknowledgment is welcome |
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15 in the documentation of your product. If for some reason you cannot |
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16 include such an acknowledgment, I would appreciate that you keep this |
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17 copyright string in the executable of your product. |
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18 */ |
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19 |
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20 /* |
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21 Build a set of tables to decode the provided canonical Huffman code. |
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22 The code lengths are lens[0..codes-1]. The result starts at *table, |
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23 whose indices are 0..2^bits-1. work is a writable array of at least |
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24 lens shorts, which is used as a work area. type is the type of code |
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25 to be generated, CODES, LENS, or DISTS. On return, zero is success, |
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26 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table |
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27 on return points to the next available entry's address. bits is the |
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28 requested root table index bits, and on return it is the actual root |
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29 table index bits. It will differ if the request is greater than the |
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30 longest code or if it is less than the shortest code. |
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31 */ |
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32 int inflate_table(type, lens, codes, table, bits, work) |
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33 codetype type; |
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34 unsigned short FAR *lens; |
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35 unsigned codes; |
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36 code FAR * FAR *table; |
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37 unsigned FAR *bits; |
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38 unsigned short FAR *work; |
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39 { |
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40 unsigned len; /* a code's length in bits */ |
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41 unsigned sym; /* index of code symbols */ |
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42 unsigned min, max; /* minimum and maximum code lengths */ |
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43 unsigned root; /* number of index bits for root table */ |
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44 unsigned curr; /* number of index bits for current table */ |
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45 unsigned drop; /* code bits to drop for sub-table */ |
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46 int left; /* number of prefix codes available */ |
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47 unsigned used; /* code entries in table used */ |
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48 unsigned huff; /* Huffman code */ |
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49 unsigned incr; /* for incrementing code, index */ |
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50 unsigned fill; /* index for replicating entries */ |
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51 unsigned low; /* low bits for current root entry */ |
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52 unsigned mask; /* mask for low root bits */ |
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53 code this; /* table entry for duplication */ |
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54 code FAR *next; /* next available space in table */ |
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55 const unsigned short FAR *base; /* base value table to use */ |
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56 const unsigned short FAR *extra; /* extra bits table to use */ |
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57 int end; /* use base and extra for symbol > end */ |
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58 unsigned short count[MAXBITS+1]; /* number of codes of each length */ |
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59 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ |
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60 static const unsigned short lbase[31] = { /* Length codes 257..285 base */ |
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61 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, |
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62 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0}; |
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63 static const unsigned short lext[31] = { /* Length codes 257..285 extra */ |
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64 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, |
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65 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 201, 196}; |
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66 static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ |
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67 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, |
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68 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, |
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69 8193, 12289, 16385, 24577, 0, 0}; |
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70 static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ |
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71 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, |
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72 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, |
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73 28, 28, 29, 29, 64, 64}; |
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74 |
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75 /* |
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76 Process a set of code lengths to create a canonical Huffman code. The |
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77 code lengths are lens[0..codes-1]. Each length corresponds to the |
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78 symbols 0..codes-1. The Huffman code is generated by first sorting the |
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79 symbols by length from short to long, and retaining the symbol order |
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80 for codes with equal lengths. Then the code starts with all zero bits |
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81 for the first code of the shortest length, and the codes are integer |
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82 increments for the same length, and zeros are appended as the length |
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83 increases. For the deflate format, these bits are stored backwards |
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84 from their more natural integer increment ordering, and so when the |
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85 decoding tables are built in the large loop below, the integer codes |
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86 are incremented backwards. |
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87 |
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88 This routine assumes, but does not check, that all of the entries in |
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89 lens[] are in the range 0..MAXBITS. The caller must assure this. |
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90 1..MAXBITS is interpreted as that code length. zero means that that |
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91 symbol does not occur in this code. |
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92 |
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93 The codes are sorted by computing a count of codes for each length, |
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94 creating from that a table of starting indices for each length in the |
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95 sorted table, and then entering the symbols in order in the sorted |
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96 table. The sorted table is work[], with that space being provided by |
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97 the caller. |
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98 |
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99 The length counts are used for other purposes as well, i.e. finding |
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100 the minimum and maximum length codes, determining if there are any |
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101 codes at all, checking for a valid set of lengths, and looking ahead |
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102 at length counts to determine sub-table sizes when building the |
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103 decoding tables. |
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104 */ |
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105 |
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106 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ |
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107 for (len = 0; len <= MAXBITS; len++) |
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108 count[len] = 0; |
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109 for (sym = 0; sym < codes; sym++) |
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110 count[lens[sym]]++; |
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111 |
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112 /* bound code lengths, force root to be within code lengths */ |
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113 root = *bits; |
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114 for (max = MAXBITS; max >= 1; max--) |
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115 if (count[max] != 0) break; |
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116 if (root > max) root = max; |
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117 if (max == 0) { /* no symbols to code at all */ |
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118 this.op = (unsigned char)64; /* invalid code marker */ |
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119 this.bits = (unsigned char)1; |
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120 this.val = (unsigned short)0; |
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121 *(*table)++ = this; /* make a table to force an error */ |
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122 *(*table)++ = this; |
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123 *bits = 1; |
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124 return 0; /* no symbols, but wait for decoding to report error */ |
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125 } |
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126 for (min = 1; min <= MAXBITS; min++) |
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127 if (count[min] != 0) break; |
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128 if (root < min) root = min; |
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129 |
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130 /* check for an over-subscribed or incomplete set of lengths */ |
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131 left = 1; |
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132 for (len = 1; len <= MAXBITS; len++) { |
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133 left <<= 1; |
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134 left -= count[len]; |
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135 if (left < 0) return -1; /* over-subscribed */ |
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136 } |
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137 if (left > 0 && (type == CODES || max != 1)) |
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138 return -1; /* incomplete set */ |
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139 |
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140 /* generate offsets into symbol table for each length for sorting */ |
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141 offs[1] = 0; |
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142 for (len = 1; len < MAXBITS; len++) |
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143 offs[len + 1] = offs[len] + count[len]; |
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144 |
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145 /* sort symbols by length, by symbol order within each length */ |
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146 for (sym = 0; sym < codes; sym++) |
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147 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; |
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148 |
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149 /* |
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150 Create and fill in decoding tables. In this loop, the table being |
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151 filled is at next and has curr index bits. The code being used is huff |
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152 with length len. That code is converted to an index by dropping drop |
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153 bits off of the bottom. For codes where len is less than drop + curr, |
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154 those top drop + curr - len bits are incremented through all values to |
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155 fill the table with replicated entries. |
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156 |
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157 root is the number of index bits for the root table. When len exceeds |
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158 root, sub-tables are created pointed to by the root entry with an index |
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159 of the low root bits of huff. This is saved in low to check for when a |
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160 new sub-table should be started. drop is zero when the root table is |
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161 being filled, and drop is root when sub-tables are being filled. |
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162 |
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163 When a new sub-table is needed, it is necessary to look ahead in the |
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164 code lengths to determine what size sub-table is needed. The length |
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165 counts are used for this, and so count[] is decremented as codes are |
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166 entered in the tables. |
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167 |
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168 used keeps track of how many table entries have been allocated from the |
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169 provided *table space. It is checked when a LENS table is being made |
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170 against the space in *table, ENOUGH, minus the maximum space needed by |
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171 the worst case distance code, MAXD. This should never happen, but the |
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172 sufficiency of ENOUGH has not been proven exhaustively, hence the check. |
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173 This assumes that when type == LENS, bits == 9. |
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174 |
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175 sym increments through all symbols, and the loop terminates when |
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176 all codes of length max, i.e. all codes, have been processed. This |
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177 routine permits incomplete codes, so another loop after this one fills |
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178 in the rest of the decoding tables with invalid code markers. |
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179 */ |
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180 |
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181 /* set up for code type */ |
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182 switch (type) { |
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183 case CODES: |
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184 base = extra = work; /* dummy value--not used */ |
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185 end = 19; |
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186 break; |
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187 case LENS: |
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188 base = lbase; |
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189 base -= 257; |
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190 extra = lext; |
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191 extra -= 257; |
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192 end = 256; |
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193 break; |
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194 default: /* DISTS */ |
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195 base = dbase; |
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196 extra = dext; |
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197 end = -1; |
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198 } |
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199 |
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200 /* initialize state for loop */ |
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201 huff = 0; /* starting code */ |
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202 sym = 0; /* starting code symbol */ |
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203 len = min; /* starting code length */ |
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204 next = *table; /* current table to fill in */ |
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205 curr = root; /* current table index bits */ |
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206 drop = 0; /* current bits to drop from code for index */ |
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207 low = (unsigned)(-1); /* trigger new sub-table when len > root */ |
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208 used = 1U << root; /* use root table entries */ |
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209 mask = used - 1; /* mask for comparing low */ |
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210 |
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211 /* check available table space */ |
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212 if (type == LENS && used >= ENOUGH - MAXD) |
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213 return 1; |
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214 |
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215 /* process all codes and make table entries */ |
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216 for (;;) { |
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217 /* create table entry */ |
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218 this.bits = (unsigned char)(len - drop); |
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219 if ((int)(work[sym]) < end) { |
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220 this.op = (unsigned char)0; |
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221 this.val = work[sym]; |
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222 } |
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223 else if ((int)(work[sym]) > end) { |
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224 this.op = (unsigned char)(extra[work[sym]]); |
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225 this.val = base[work[sym]]; |
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226 } |
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227 else { |
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228 this.op = (unsigned char)(32 + 64); /* end of block */ |
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229 this.val = 0; |
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230 } |
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231 |
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232 /* replicate for those indices with low len bits equal to huff */ |
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233 incr = 1U << (len - drop); |
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234 fill = 1U << curr; |
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235 min = fill; /* save offset to next table */ |
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236 do { |
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237 fill -= incr; |
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238 next[(huff >> drop) + fill] = this; |
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239 } while (fill != 0); |
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240 |
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241 /* backwards increment the len-bit code huff */ |
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242 incr = 1U << (len - 1); |
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243 while (huff & incr) |
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244 incr >>= 1; |
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245 if (incr != 0) { |
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246 huff &= incr - 1; |
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247 huff += incr; |
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248 } |
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249 else |
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250 huff = 0; |
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251 |
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252 /* go to next symbol, update count, len */ |
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253 sym++; |
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254 if (--(count[len]) == 0) { |
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255 if (len == max) break; |
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256 len = lens[work[sym]]; |
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257 } |
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258 |
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259 /* create new sub-table if needed */ |
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260 if (len > root && (huff & mask) != low) { |
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261 /* if first time, transition to sub-tables */ |
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262 if (drop == 0) |
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263 drop = root; |
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264 |
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265 /* increment past last table */ |
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266 next += min; /* here min is 1 << curr */ |
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267 |
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268 /* determine length of next table */ |
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269 curr = len - drop; |
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270 left = (int)(1 << curr); |
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271 while (curr + drop < max) { |
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272 left -= count[curr + drop]; |
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273 if (left <= 0) break; |
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274 curr++; |
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275 left <<= 1; |
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276 } |
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277 |
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278 /* check for enough space */ |
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279 used += 1U << curr; |
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280 if (type == LENS && used >= ENOUGH - MAXD) |
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281 return 1; |
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282 |
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283 /* point entry in root table to sub-table */ |
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284 low = huff & mask; |
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285 (*table)[low].op = (unsigned char)curr; |
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286 (*table)[low].bits = (unsigned char)root; |
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287 (*table)[low].val = (unsigned short)(next - *table); |
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288 } |
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289 } |
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290 |
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291 /* |
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292 Fill in rest of table for incomplete codes. This loop is similar to the |
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293 loop above in incrementing huff for table indices. It is assumed that |
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294 len is equal to curr + drop, so there is no loop needed to increment |
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295 through high index bits. When the current sub-table is filled, the loop |
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296 drops back to the root table to fill in any remaining entries there. |
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297 */ |
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298 this.op = (unsigned char)64; /* invalid code marker */ |
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299 this.bits = (unsigned char)(len - drop); |
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300 this.val = (unsigned short)0; |
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301 while (huff != 0) { |
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302 /* when done with sub-table, drop back to root table */ |
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303 if (drop != 0 && (huff & mask) != low) { |
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304 drop = 0; |
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305 len = root; |
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306 next = *table; |
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307 this.bits = (unsigned char)len; |
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308 } |
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309 |
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310 /* put invalid code marker in table */ |
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311 next[huff >> drop] = this; |
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312 |
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313 /* backwards increment the len-bit code huff */ |
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314 incr = 1U << (len - 1); |
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315 while (huff & incr) |
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316 incr >>= 1; |
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317 if (incr != 0) { |
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318 huff &= incr - 1; |
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319 huff += incr; |
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320 } |
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321 else |
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322 huff = 0; |
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323 } |
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324 |
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325 /* set return parameters */ |
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326 *table += used; |
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327 *bits = root; |
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328 return 0; |
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329 } |