Mercurial > repos > blastem
annotate zlib/inftrees.c @ 1952:42c12d141f6e
Remove usage of GCC pointer arithmetic on void * extension
author | Michael Pavone <pavone@retrodev.com> |
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date | Thu, 30 Apr 2020 23:30:22 -0700 |
parents | 00d788dac91a |
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1 /* inftrees.c -- generate Huffman trees for efficient decoding |
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2 * Copyright (C) 1995-2017 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 1.2.11 Copyright 1995-2017 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 ZLIB_INTERNAL 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 here; /* 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 unsigned match; /* use base and extra for symbol >= match */ |
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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, 77, 202}; |
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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 here.op = (unsigned char)64; /* invalid code marker */ |
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119 here.bits = (unsigned char)1; |
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120 here.val = (unsigned short)0; |
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121 *(*table)++ = here; /* make a table to force an error */ |
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122 *(*table)++ = here; |
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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 < max; 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 for LENS and DIST tables against |
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170 the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in |
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171 the initial root table size constants. See the comments in inftrees.h |
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172 for more information. |
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173 |
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174 sym increments through all symbols, and the loop terminates when |
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175 all codes of length max, i.e. all codes, have been processed. This |
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176 routine permits incomplete codes, so another loop after this one fills |
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177 in the rest of the decoding tables with invalid code markers. |
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178 */ |
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179 |
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180 /* set up for code type */ |
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181 switch (type) { |
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182 case CODES: |
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183 base = extra = work; /* dummy value--not used */ |
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184 match = 20; |
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185 break; |
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186 case LENS: |
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187 base = lbase; |
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188 extra = lext; |
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189 match = 257; |
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190 break; |
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191 default: /* DISTS */ |
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192 base = dbase; |
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193 extra = dext; |
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194 match = 0; |
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195 } |
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196 |
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197 /* initialize state for loop */ |
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198 huff = 0; /* starting code */ |
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199 sym = 0; /* starting code symbol */ |
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200 len = min; /* starting code length */ |
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201 next = *table; /* current table to fill in */ |
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202 curr = root; /* current table index bits */ |
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203 drop = 0; /* current bits to drop from code for index */ |
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204 low = (unsigned)(-1); /* trigger new sub-table when len > root */ |
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205 used = 1U << root; /* use root table entries */ |
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206 mask = used - 1; /* mask for comparing low */ |
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207 |
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208 /* check available table space */ |
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209 if ((type == LENS && used > ENOUGH_LENS) || |
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210 (type == DISTS && used > ENOUGH_DISTS)) |
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211 return 1; |
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212 |
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213 /* process all codes and make table entries */ |
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214 for (;;) { |
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215 /* create table entry */ |
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216 here.bits = (unsigned char)(len - drop); |
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217 if (work[sym] + 1U < match) { |
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218 here.op = (unsigned char)0; |
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219 here.val = work[sym]; |
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220 } |
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221 else if (work[sym] >= match) { |
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222 here.op = (unsigned char)(extra[work[sym] - match]); |
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223 here.val = base[work[sym] - match]; |
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224 } |
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225 else { |
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226 here.op = (unsigned char)(32 + 64); /* end of block */ |
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227 here.val = 0; |
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228 } |
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229 |
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230 /* replicate for those indices with low len bits equal to huff */ |
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231 incr = 1U << (len - drop); |
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232 fill = 1U << curr; |
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233 min = fill; /* save offset to next table */ |
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234 do { |
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235 fill -= incr; |
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236 next[(huff >> drop) + fill] = here; |
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237 } while (fill != 0); |
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238 |
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239 /* backwards increment the len-bit code huff */ |
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240 incr = 1U << (len - 1); |
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241 while (huff & incr) |
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242 incr >>= 1; |
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243 if (incr != 0) { |
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244 huff &= incr - 1; |
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245 huff += incr; |
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246 } |
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247 else |
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248 huff = 0; |
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249 |
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250 /* go to next symbol, update count, len */ |
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251 sym++; |
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252 if (--(count[len]) == 0) { |
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253 if (len == max) break; |
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254 len = lens[work[sym]]; |
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255 } |
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256 |
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257 /* create new sub-table if needed */ |
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258 if (len > root && (huff & mask) != low) { |
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259 /* if first time, transition to sub-tables */ |
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260 if (drop == 0) |
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261 drop = root; |
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262 |
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263 /* increment past last table */ |
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264 next += min; /* here min is 1 << curr */ |
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265 |
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266 /* determine length of next table */ |
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267 curr = len - drop; |
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268 left = (int)(1 << curr); |
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269 while (curr + drop < max) { |
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270 left -= count[curr + drop]; |
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271 if (left <= 0) break; |
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272 curr++; |
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273 left <<= 1; |
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274 } |
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275 |
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276 /* check for enough space */ |
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277 used += 1U << curr; |
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278 if ((type == LENS && used > ENOUGH_LENS) || |
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279 (type == DISTS && used > ENOUGH_DISTS)) |
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280 return 1; |
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281 |
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282 /* point entry in root table to sub-table */ |
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283 low = huff & mask; |
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284 (*table)[low].op = (unsigned char)curr; |
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285 (*table)[low].bits = (unsigned char)root; |
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286 (*table)[low].val = (unsigned short)(next - *table); |
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287 } |
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288 } |
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289 |
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290 /* fill in remaining table entry if code is incomplete (guaranteed to have |
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291 at most one remaining entry, since if the code is incomplete, the |
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292 maximum code length that was allowed to get this far is one bit) */ |
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293 if (huff != 0) { |
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294 here.op = (unsigned char)64; /* invalid code marker */ |
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295 here.bits = (unsigned char)(len - drop); |
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296 here.val = (unsigned short)0; |
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297 next[huff] = here; |
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298 } |
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299 |
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300 /* set return parameters */ |
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301 *table += used; |
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302 *bits = root; |
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303 return 0; |
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304 } |