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4349 | Serge | 1 | /* inftrees.c -- generate Huffman trees for efficient decoding |
2 | * Copyright (C) 1995-2013 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 | |||
6 | #include "zutil.h" |
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7 | #include "inftrees.h" |
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8 | |||
9 | #define MAXBITS 15 |
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10 | |||
11 | const char inflate_copyright[] = |
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12 | " inflate 1.2.8 Copyright 1995-2013 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 | |||
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 | 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, 72, 78}; |
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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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | end = 19; |
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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 | base -= 257; |
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189 | extra = lext; |
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190 | extra -= 257; |
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191 | end = 256; |
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192 | break; |
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193 | default: /* DISTS */ |
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194 | base = dbase; |
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195 | extra = dext; |
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196 | end = -1; |
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197 | } |
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198 | |||
199 | /* initialize state for loop */ |
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200 | huff = 0; /* starting code */ |
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201 | sym = 0; /* starting code symbol */ |
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202 | len = min; /* starting code length */ |
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203 | next = *table; /* current table to fill in */ |
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204 | curr = root; /* current table index bits */ |
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205 | drop = 0; /* current bits to drop from code for index */ |
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206 | low = (unsigned)(-1); /* trigger new sub-table when len > root */ |
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207 | used = 1U << root; /* use root table entries */ |
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208 | mask = used - 1; /* mask for comparing low */ |
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209 | |||
210 | /* check available table space */ |
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211 | if ((type == LENS && used > ENOUGH_LENS) || |
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212 | (type == DISTS && used > ENOUGH_DISTS)) |
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213 | return 1; |
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214 | |||
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 | here.bits = (unsigned char)(len - drop); |
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219 | if ((int)(work[sym]) < end) { |
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220 | here.op = (unsigned char)0; |
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221 | here.val = work[sym]; |
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222 | } |
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223 | else if ((int)(work[sym]) > end) { |
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224 | here.op = (unsigned char)(extra[work[sym]]); |
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225 | here.val = base[work[sym]]; |
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226 | } |
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227 | else { |
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228 | here.op = (unsigned char)(32 + 64); /* end of block */ |
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229 | here.val = 0; |
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230 | } |
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231 | |||
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] = here; |
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239 | } while (fill != 0); |
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240 | |||
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 | |||
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 | |||
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 | |||
265 | /* increment past last table */ |
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266 | next += min; /* here min is 1 << curr */ |
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267 | |||
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 | |||
278 | /* check for enough space */ |
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279 | used += 1U << curr; |
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280 | if ((type == LENS && used > ENOUGH_LENS) || |
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281 | (type == DISTS && used > ENOUGH_DISTS)) |
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282 | return 1; |
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283 | |||
284 | /* point entry in root table to sub-table */ |
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285 | low = huff & mask; |
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286 | (*table)[low].op = (unsigned char)curr; |
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287 | (*table)[low].bits = (unsigned char)root; |
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288 | (*table)[low].val = (unsigned short)(next - *table); |
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289 | } |
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290 | } |
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291 | |||
292 | /* fill in remaining table entry if code is incomplete (guaranteed to have |
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293 | at most one remaining entry, since if the code is incomplete, the |
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294 | maximum code length that was allowed to get this far is one bit) */ |
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295 | if (huff != 0) { |
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296 | here.op = (unsigned char)64; /* invalid code marker */ |
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297 | here.bits = (unsigned char)(len - drop); |
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298 | here.val = (unsigned short)0; |
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299 | next[huff] = here; |
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300 | } |
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301 | |||
302 | /* set return parameters */ |
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303 | *table += used; |
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304 | *bits = root; |
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305 | return 0; |
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306 | }><>=><=>=>>><>><>><>><>><>>><>>>>=><=>=>>>>=> |