1 /* 2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 3 * 4 * This code is free software; you can redistribute it and/or modify it 5 * under the terms of the GNU General Public License version 2 only, as 6 * published by the Free Software Foundation. Oracle designates this 7 * particular file as subject to the "Classpath" exception as provided 8 * by Oracle in the LICENSE file that accompanied this code. 9 * 10 * This code is distributed in the hope that it will be useful, but WITHOUT 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 13 * version 2 for more details (a copy is included in the LICENSE file that 14 * accompanied this code). 15 * 16 * You should have received a copy of the GNU General Public License version 17 * 2 along with this work; if not, write to the Free Software Foundation, 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 19 * 20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 21 * or visit www.oracle.com if you need additional information or have any 22 * questions. 23 */ 24 25 /* inftrees.c -- generate Huffman trees for efficient decoding 26 * Copyright (C) 1995-2022 Mark Adler 27 * For conditions of distribution and use, see copyright notice in zlib.h 28 */ 29 30 #include "zutil.h" 31 #include "inftrees.h" 32 33 #define MAXBITS 15 34 35 const char inflate_copyright[] = 36 " inflate 1.2.13 Copyright 1995-2022 Mark Adler "; 37 /* 38 If you use the zlib library in a product, an acknowledgment is welcome 39 in the documentation of your product. If for some reason you cannot 40 include such an acknowledgment, I would appreciate that you keep this 41 copyright string in the executable of your product. 42 */ 43 44 /* 45 Build a set of tables to decode the provided canonical Huffman code. 46 The code lengths are lens[0..codes-1]. The result starts at *table, 47 whose indices are 0..2^bits-1. work is a writable array of at least 48 lens shorts, which is used as a work area. type is the type of code 49 to be generated, CODES, LENS, or DISTS. On return, zero is success, 50 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table 51 on return points to the next available entry's address. bits is the 52 requested root table index bits, and on return it is the actual root 53 table index bits. It will differ if the request is greater than the 54 longest code or if it is less than the shortest code. 55 */ 56 int ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work) 57 codetype type; 58 unsigned short FAR *lens; 59 unsigned codes; 60 code FAR * FAR *table; 61 unsigned FAR *bits; 62 unsigned short FAR *work; 63 { 64 unsigned len; /* a code's length in bits */ 65 unsigned sym; /* index of code symbols */ 66 unsigned min, max; /* minimum and maximum code lengths */ 67 unsigned root; /* number of index bits for root table */ 68 unsigned curr; /* number of index bits for current table */ 69 unsigned drop; /* code bits to drop for sub-table */ 70 int left; /* number of prefix codes available */ 71 unsigned used; /* code entries in table used */ 72 unsigned huff; /* Huffman code */ 73 unsigned incr; /* for incrementing code, index */ 74 unsigned fill; /* index for replicating entries */ 75 unsigned low; /* low bits for current root entry */ 76 unsigned mask; /* mask for low root bits */ 77 code here; /* table entry for duplication */ 78 code FAR *next; /* next available space in table */ 79 const unsigned short FAR *base; /* base value table to use */ 80 const unsigned short FAR *extra; /* extra bits table to use */ 81 unsigned match; /* use base and extra for symbol >= match */ 82 unsigned short count[MAXBITS+1]; /* number of codes of each length */ 83 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ 84 static const unsigned short lbase[31] = { /* Length codes 257..285 base */ 85 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 86 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0}; 87 static const unsigned short lext[31] = { /* Length codes 257..285 extra */ 88 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 89 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 194, 65}; 90 static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ 91 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 92 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 93 8193, 12289, 16385, 24577, 0, 0}; 94 static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ 95 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 96 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 97 28, 28, 29, 29, 64, 64}; 98 99 /* 100 Process a set of code lengths to create a canonical Huffman code. The 101 code lengths are lens[0..codes-1]. Each length corresponds to the 102 symbols 0..codes-1. The Huffman code is generated by first sorting the 103 symbols by length from short to long, and retaining the symbol order 104 for codes with equal lengths. Then the code starts with all zero bits 105 for the first code of the shortest length, and the codes are integer 106 increments for the same length, and zeros are appended as the length 107 increases. For the deflate format, these bits are stored backwards 108 from their more natural integer increment ordering, and so when the 109 decoding tables are built in the large loop below, the integer codes 110 are incremented backwards. 111 112 This routine assumes, but does not check, that all of the entries in 113 lens[] are in the range 0..MAXBITS. The caller must assure this. 114 1..MAXBITS is interpreted as that code length. zero means that that 115 symbol does not occur in this code. 116 117 The codes are sorted by computing a count of codes for each length, 118 creating from that a table of starting indices for each length in the 119 sorted table, and then entering the symbols in order in the sorted 120 table. The sorted table is work[], with that space being provided by 121 the caller. 122 123 The length counts are used for other purposes as well, i.e. finding 124 the minimum and maximum length codes, determining if there are any 125 codes at all, checking for a valid set of lengths, and looking ahead 126 at length counts to determine sub-table sizes when building the 127 decoding tables. 128 */ 129 130 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ 131 for (len = 0; len <= MAXBITS; len++) 132 count[len] = 0; 133 for (sym = 0; sym < codes; sym++) 134 count[lens[sym]]++; 135 136 /* bound code lengths, force root to be within code lengths */ 137 root = *bits; 138 for (max = MAXBITS; max >= 1; max--) 139 if (count[max] != 0) break; 140 if (root > max) root = max; 141 if (max == 0) { /* no symbols to code at all */ 142 here.op = (unsigned char)64; /* invalid code marker */ 143 here.bits = (unsigned char)1; 144 here.val = (unsigned short)0; 145 *(*table)++ = here; /* make a table to force an error */ 146 *(*table)++ = here; 147 *bits = 1; 148 return 0; /* no symbols, but wait for decoding to report error */ 149 } 150 for (min = 1; min < max; min++) 151 if (count[min] != 0) break; 152 if (root < min) root = min; 153 154 /* check for an over-subscribed or incomplete set of lengths */ 155 left = 1; 156 for (len = 1; len <= MAXBITS; len++) { 157 left <<= 1; 158 left -= count[len]; 159 if (left < 0) return -1; /* over-subscribed */ 160 } 161 if (left > 0 && (type == CODES || max != 1)) 162 return -1; /* incomplete set */ 163 164 /* generate offsets into symbol table for each length for sorting */ 165 offs[1] = 0; 166 for (len = 1; len < MAXBITS; len++) 167 offs[len + 1] = offs[len] + count[len]; 168 169 /* sort symbols by length, by symbol order within each length */ 170 for (sym = 0; sym < codes; sym++) 171 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; 172 173 /* 174 Create and fill in decoding tables. In this loop, the table being 175 filled is at next and has curr index bits. The code being used is huff 176 with length len. That code is converted to an index by dropping drop 177 bits off of the bottom. For codes where len is less than drop + curr, 178 those top drop + curr - len bits are incremented through all values to 179 fill the table with replicated entries. 180 181 root is the number of index bits for the root table. When len exceeds 182 root, sub-tables are created pointed to by the root entry with an index 183 of the low root bits of huff. This is saved in low to check for when a 184 new sub-table should be started. drop is zero when the root table is 185 being filled, and drop is root when sub-tables are being filled. 186 187 When a new sub-table is needed, it is necessary to look ahead in the 188 code lengths to determine what size sub-table is needed. The length 189 counts are used for this, and so count[] is decremented as codes are 190 entered in the tables. 191 192 used keeps track of how many table entries have been allocated from the 193 provided *table space. It is checked for LENS and DIST tables against 194 the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in 195 the initial root table size constants. See the comments in inftrees.h 196 for more information. 197 198 sym increments through all symbols, and the loop terminates when 199 all codes of length max, i.e. all codes, have been processed. This 200 routine permits incomplete codes, so another loop after this one fills 201 in the rest of the decoding tables with invalid code markers. 202 */ 203 204 /* set up for code type */ 205 switch (type) { 206 case CODES: 207 base = extra = work; /* dummy value--not used */ 208 match = 20; 209 break; 210 case LENS: 211 base = lbase; 212 extra = lext; 213 match = 257; 214 break; 215 default: /* DISTS */ 216 base = dbase; 217 extra = dext; 218 match = 0; 219 } 220 221 /* initialize state for loop */ 222 huff = 0; /* starting code */ 223 sym = 0; /* starting code symbol */ 224 len = min; /* starting code length */ 225 next = *table; /* current table to fill in */ 226 curr = root; /* current table index bits */ 227 drop = 0; /* current bits to drop from code for index */ 228 low = (unsigned)(-1); /* trigger new sub-table when len > root */ 229 used = 1U << root; /* use root table entries */ 230 mask = used - 1; /* mask for comparing low */ 231 232 /* check available table space */ 233 if ((type == LENS && used > ENOUGH_LENS) || 234 (type == DISTS && used > ENOUGH_DISTS)) 235 return 1; 236 237 /* process all codes and make table entries */ 238 for (;;) { 239 /* create table entry */ 240 here.bits = (unsigned char)(len - drop); 241 if (work[sym] + 1U < match) { 242 here.op = (unsigned char)0; 243 here.val = work[sym]; 244 } 245 else if (work[sym] >= match) { 246 here.op = (unsigned char)(extra[work[sym] - match]); 247 here.val = base[work[sym] - match]; 248 } 249 else { 250 here.op = (unsigned char)(32 + 64); /* end of block */ 251 here.val = 0; 252 } 253 254 /* replicate for those indices with low len bits equal to huff */ 255 incr = 1U << (len - drop); 256 fill = 1U << curr; 257 min = fill; /* save offset to next table */ 258 do { 259 fill -= incr; 260 next[(huff >> drop) + fill] = here; 261 } while (fill != 0); 262 263 /* backwards increment the len-bit code huff */ 264 incr = 1U << (len - 1); 265 while (huff & incr) 266 incr >>= 1; 267 if (incr != 0) { 268 huff &= incr - 1; 269 huff += incr; 270 } 271 else 272 huff = 0; 273 274 /* go to next symbol, update count, len */ 275 sym++; 276 if (--(count[len]) == 0) { 277 if (len == max) break; 278 len = lens[work[sym]]; 279 } 280 281 /* create new sub-table if needed */ 282 if (len > root && (huff & mask) != low) { 283 /* if first time, transition to sub-tables */ 284 if (drop == 0) 285 drop = root; 286 287 /* increment past last table */ 288 next += min; /* here min is 1 << curr */ 289 290 /* determine length of next table */ 291 curr = len - drop; 292 left = (int)(1 << curr); 293 while (curr + drop < max) { 294 left -= count[curr + drop]; 295 if (left <= 0) break; 296 curr++; 297 left <<= 1; 298 } 299 300 /* check for enough space */ 301 used += 1U << curr; 302 if ((type == LENS && used > ENOUGH_LENS) || 303 (type == DISTS && used > ENOUGH_DISTS)) 304 return 1; 305 306 /* point entry in root table to sub-table */ 307 low = huff & mask; 308 (*table)[low].op = (unsigned char)curr; 309 (*table)[low].bits = (unsigned char)root; 310 (*table)[low].val = (unsigned short)(next - *table); 311 } 312 } 313 314 /* fill in remaining table entry if code is incomplete (guaranteed to have 315 at most one remaining entry, since if the code is incomplete, the 316 maximum code length that was allowed to get this far is one bit) */ 317 if (huff != 0) { 318 here.op = (unsigned char)64; /* invalid code marker */ 319 here.bits = (unsigned char)(len - drop); 320 here.val = (unsigned short)0; 321 next[huff] = here; 322 } 323 324 /* set return parameters */ 325 *table += used; 326 *bits = root; 327 return 0; 328 }