1 /* inftrees.c -- generate Huffman trees for efficient decoding 2 * Copyright (C) 1995-2022 Mark Adler 3 * For conditions of distribution and use, see copyright notice in zlib.h 4 */ 5 6 #include "zutil.h" 7 #include "inftrees.h" 8 9 #define MAXBITS 15 10 11 const char inflate_copyright[] = 12 " inflate 1.2.12 Copyright 1995-2022 Mark Adler "; 13 /* 14 If you use the zlib library in a product, an acknowledgment is welcome 15 in the documentation of your product. If for some reason you cannot 16 include such an acknowledgment, I would appreciate that you keep this 17 copyright string in the executable of your product. 18 */ 19 20 /* 21 Build a set of tables to decode the provided canonical Huffman code. 22 The code lengths are lens[0..codes-1]. The result starts at *table, 23 whose indices are 0..2^bits-1. work is a writable array of at least 24 lens shorts, which is used as a work area. type is the type of code 25 to be generated, CODES, LENS, or DISTS. On return, zero is success, 26 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table 27 on return points to the next available entry's address. bits is the 28 requested root table index bits, and on return it is the actual root 29 table index bits. It will differ if the request is greater than the 30 longest code or if it is less than the shortest code. 31 */ 32 int ZLIB_INTERNAL inflate_table(codetype type, unsigned short FAR *lens, 33 unsigned codes, code FAR * FAR *table, unsigned FAR *bits, 34 unsigned short FAR *work) 35 { 36 unsigned len; /* a code's length in bits */ 37 unsigned sym; /* index of code symbols */ 38 unsigned min, max; /* minimum and maximum code lengths */ 39 unsigned root; /* number of index bits for root table */ 40 unsigned curr; /* number of index bits for current table */ 41 unsigned drop; /* code bits to drop for sub-table */ 42 int left; /* number of prefix codes available */ 43 unsigned used; /* code entries in table used */ 44 unsigned huff; /* Huffman code */ 45 unsigned incr; /* for incrementing code, index */ 46 unsigned fill; /* index for replicating entries */ 47 unsigned low; /* low bits for current root entry */ 48 unsigned mask; /* mask for low root bits */ 49 code here; /* table entry for duplication */ 50 code FAR *next; /* next available space in table */ 51 const unsigned short FAR *base; /* base value table to use */ 52 const unsigned short FAR *extra; /* extra bits table to use */ 53 unsigned match; /* use base and extra for symbol >= match */ 54 unsigned short count[MAXBITS+1]; /* number of codes of each length */ 55 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ 56 static const unsigned short lbase[31] = { /* Length codes 257..285 base */ 57 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 58 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0}; 59 static const unsigned short lext[31] = { /* Length codes 257..285 extra */ 60 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 61 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 199, 202}; 62 static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ 63 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 64 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 65 8193, 12289, 16385, 24577, 0, 0}; 66 static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ 67 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 68 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 69 28, 28, 29, 29, 64, 64}; 70 71 /* 72 Process a set of code lengths to create a canonical Huffman code. The 73 code lengths are lens[0..codes-1]. Each length corresponds to the 74 symbols 0..codes-1. The Huffman code is generated by first sorting the 75 symbols by length from short to long, and retaining the symbol order 76 for codes with equal lengths. Then the code starts with all zero bits 77 for the first code of the shortest length, and the codes are integer 78 increments for the same length, and zeros are appended as the length 79 increases. For the deflate format, these bits are stored backwards 80 from their more natural integer increment ordering, and so when the 81 decoding tables are built in the large loop below, the integer codes 82 are incremented backwards. 83 84 This routine assumes, but does not check, that all of the entries in 85 lens[] are in the range 0..MAXBITS. The caller must assure this. 86 1..MAXBITS is interpreted as that code length. zero means that that 87 symbol does not occur in this code. 88 89 The codes are sorted by computing a count of codes for each length, 90 creating from that a table of starting indices for each length in the 91 sorted table, and then entering the symbols in order in the sorted 92 table. The sorted table is work[], with that space being provided by 93 the caller. 94 95 The length counts are used for other purposes as well, i.e. finding 96 the minimum and maximum length codes, determining if there are any 97 codes at all, checking for a valid set of lengths, and looking ahead 98 at length counts to determine sub-table sizes when building the 99 decoding tables. 100 */ 101 102 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ 103 for (len = 0; len <= MAXBITS; len++) 104 count[len] = 0; 105 for (sym = 0; sym < codes; sym++) 106 count[lens[sym]]++; 107 108 /* bound code lengths, force root to be within code lengths */ 109 root = *bits; 110 for (max = MAXBITS; max >= 1; max--) 111 if (count[max] != 0) break; 112 if (root > max) root = max; 113 if (max == 0) { /* no symbols to code at all */ 114 here.op = (unsigned char)64; /* invalid code marker */ 115 here.bits = (unsigned char)1; 116 here.val = (unsigned short)0; 117 *(*table)++ = here; /* make a table to force an error */ 118 *(*table)++ = here; 119 *bits = 1; 120 return 0; /* no symbols, but wait for decoding to report error */ 121 } 122 for (min = 1; min < max; min++) 123 if (count[min] != 0) break; 124 if (root < min) root = min; 125 126 /* check for an over-subscribed or incomplete set of lengths */ 127 left = 1; 128 for (len = 1; len <= MAXBITS; len++) { 129 left <<= 1; 130 left -= count[len]; 131 if (left < 0) return -1; /* over-subscribed */ 132 } 133 if (left > 0 && (type == CODES || max != 1)) 134 return -1; /* incomplete set */ 135 136 /* generate offsets into symbol table for each length for sorting */ 137 offs[1] = 0; 138 for (len = 1; len < MAXBITS; len++) 139 offs[len + 1] = offs[len] + count[len]; 140 141 /* sort symbols by length, by symbol order within each length */ 142 for (sym = 0; sym < codes; sym++) 143 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; 144 145 /* 146 Create and fill in decoding tables. In this loop, the table being 147 filled is at next and has curr index bits. The code being used is huff 148 with length len. That code is converted to an index by dropping drop 149 bits off of the bottom. For codes where len is less than drop + curr, 150 those top drop + curr - len bits are incremented through all values to 151 fill the table with replicated entries. 152 153 root is the number of index bits for the root table. When len exceeds 154 root, sub-tables are created pointed to by the root entry with an index 155 of the low root bits of huff. This is saved in low to check for when a 156 new sub-table should be started. drop is zero when the root table is 157 being filled, and drop is root when sub-tables are being filled. 158 159 When a new sub-table is needed, it is necessary to look ahead in the 160 code lengths to determine what size sub-table is needed. The length 161 counts are used for this, and so count[] is decremented as codes are 162 entered in the tables. 163 164 used keeps track of how many table entries have been allocated from the 165 provided *table space. It is checked for LENS and DIST tables against 166 the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in 167 the initial root table size constants. See the comments in inftrees.h 168 for more information. 169 170 sym increments through all symbols, and the loop terminates when 171 all codes of length max, i.e. all codes, have been processed. This 172 routine permits incomplete codes, so another loop after this one fills 173 in the rest of the decoding tables with invalid code markers. 174 */ 175 176 /* set up for code type */ 177 switch (type) { 178 case CODES: 179 base = extra = work; /* dummy value--not used */ 180 match = 20; 181 break; 182 case LENS: 183 base = lbase; 184 extra = lext; 185 match = 257; 186 break; 187 default: /* DISTS */ 188 base = dbase; 189 extra = dext; 190 match = 0; 191 } 192 193 /* initialize state for loop */ 194 huff = 0; /* starting code */ 195 sym = 0; /* starting code symbol */ 196 len = min; /* starting code length */ 197 next = *table; /* current table to fill in */ 198 curr = root; /* current table index bits */ 199 drop = 0; /* current bits to drop from code for index */ 200 low = (unsigned)(-1); /* trigger new sub-table when len > root */ 201 used = 1U << root; /* use root table entries */ 202 mask = used - 1; /* mask for comparing low */ 203 204 /* check available table space */ 205 if ((type == LENS && used > ENOUGH_LENS) || 206 (type == DISTS && used > ENOUGH_DISTS)) 207 return 1; 208 209 /* process all codes and make table entries */ 210 for (;;) { 211 /* create table entry */ 212 here.bits = (unsigned char)(len - drop); 213 if (work[sym] + 1U < match) { 214 here.op = (unsigned char)0; 215 here.val = work[sym]; 216 } 217 else if (work[sym] >= match) { 218 here.op = (unsigned char)(extra[work[sym] - match]); 219 here.val = base[work[sym] - match]; 220 } 221 else { 222 here.op = (unsigned char)(32 + 64); /* end of block */ 223 here.val = 0; 224 } 225 226 /* replicate for those indices with low len bits equal to huff */ 227 incr = 1U << (len - drop); 228 fill = 1U << curr; 229 min = fill; /* save offset to next table */ 230 do { 231 fill -= incr; 232 next[(huff >> drop) + fill] = here; 233 } while (fill != 0); 234 235 /* backwards increment the len-bit code huff */ 236 incr = 1U << (len - 1); 237 while (huff & incr) 238 incr >>= 1; 239 if (incr != 0) { 240 huff &= incr - 1; 241 huff += incr; 242 } 243 else 244 huff = 0; 245 246 /* go to next symbol, update count, len */ 247 sym++; 248 if (--(count[len]) == 0) { 249 if (len == max) break; 250 len = lens[work[sym]]; 251 } 252 253 /* create new sub-table if needed */ 254 if (len > root && (huff & mask) != low) { 255 /* if first time, transition to sub-tables */ 256 if (drop == 0) 257 drop = root; 258 259 /* increment past last table */ 260 next += min; /* here min is 1 << curr */ 261 262 /* determine length of next table */ 263 curr = len - drop; 264 left = (int)(1 << curr); 265 while (curr + drop < max) { 266 left -= count[curr + drop]; 267 if (left <= 0) break; 268 curr++; 269 left <<= 1; 270 } 271 272 /* check for enough space */ 273 used += 1U << curr; 274 if ((type == LENS && used > ENOUGH_LENS) || 275 (type == DISTS && used > ENOUGH_DISTS)) 276 return 1; 277 278 /* point entry in root table to sub-table */ 279 low = huff & mask; 280 (*table)[low].op = (unsigned char)curr; 281 (*table)[low].bits = (unsigned char)root; 282 (*table)[low].val = (unsigned short)(next - *table); 283 } 284 } 285 286 /* fill in remaining table entry if code is incomplete (guaranteed to have 287 at most one remaining entry, since if the code is incomplete, the 288 maximum code length that was allowed to get this far is one bit) */ 289 if (huff != 0) { 290 here.op = (unsigned char)64; /* invalid code marker */ 291 here.bits = (unsigned char)(len - drop); 292 here.val = (unsigned short)0; 293 next[huff] = here; 294 } 295 296 /* set return parameters */ 297 *table += used; 298 *bits = root; 299 return 0; 300 } 301