1/* inftree9.c -- generate Huffman trees for efficient decoding 2 * Copyright (C) 1995-2024 Mark Adler 3 * For conditions of distribution and use, see copyright notice in zlib.h 4 */ 5 6#include "zutil.h" 7#include "inftree9.h" 8 9#define MAXBITS 15 10 11const char inflate9_copyright[] = 12 " inflate9 1.3.1 Copyright 1995-2024 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 */ 32int inflate_table9(codetype type, unsigned short FAR *lens, unsigned codes, 33 code FAR * FAR *table, unsigned FAR *bits, 34 unsigned short FAR *work) { 35 unsigned len; /* a code's length in bits */ 36 unsigned sym; /* index of code symbols */ 37 unsigned min, max; /* minimum and maximum code lengths */ 38 unsigned root; /* number of index bits for root table */ 39 unsigned curr; /* number of index bits for current table */ 40 unsigned drop; /* code bits to drop for sub-table */ 41 int left; /* number of prefix codes available */ 42 unsigned used; /* code entries in table used */ 43 unsigned huff; /* Huffman code */ 44 unsigned incr; /* for incrementing code, index */ 45 unsigned fill; /* index for replicating entries */ 46 unsigned low; /* low bits for current root entry */ 47 unsigned mask; /* mask for low root bits */ 48 code this; /* table entry for duplication */ 49 code FAR *next; /* next available space in table */ 50 const unsigned short FAR *base; /* base value table to use */ 51 const unsigned short FAR *extra; /* extra bits table to use */ 52 int end; /* use base and extra for symbol > end */ 53 unsigned short count[MAXBITS+1]; /* number of codes of each length */ 54 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ 55 static const unsigned short lbase[31] = { /* Length codes 257..285 base */ 56 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 57 19, 23, 27, 31, 35, 43, 51, 59, 67, 83, 99, 115, 58 131, 163, 195, 227, 3, 0, 0}; 59 static const unsigned short lext[31] = { /* Length codes 257..285 extra */ 60 128, 128, 128, 128, 128, 128, 128, 128, 129, 129, 129, 129, 61 130, 130, 130, 130, 131, 131, 131, 131, 132, 132, 132, 132, 62 133, 133, 133, 133, 144, 203, 77}; 63 static const unsigned short dbase[32] = { /* Distance codes 0..31 base */ 64 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65 65, 97, 129, 193, 257, 385, 513, 769, 1025, 1537, 2049, 3073, 66 4097, 6145, 8193, 12289, 16385, 24577, 32769, 49153}; 67 static const unsigned short dext[32] = { /* Distance codes 0..31 extra */ 68 128, 128, 128, 128, 129, 129, 130, 130, 131, 131, 132, 132, 69 133, 133, 134, 134, 135, 135, 136, 136, 137, 137, 138, 138, 70 139, 139, 140, 140, 141, 141, 142, 142}; 71 72 /* 73 Process a set of code lengths to create a canonical Huffman code. The 74 code lengths are lens[0..codes-1]. Each length corresponds to the 75 symbols 0..codes-1. The Huffman code is generated by first sorting the 76 symbols by length from short to long, and retaining the symbol order 77 for codes with equal lengths. Then the code starts with all zero bits 78 for the first code of the shortest length, and the codes are integer 79 increments for the same length, and zeros are appended as the length 80 increases. For the deflate format, these bits are stored backwards 81 from their more natural integer increment ordering, and so when the 82 decoding tables are built in the large loop below, the integer codes 83 are incremented backwards. 84 85 This routine assumes, but does not check, that all of the entries in 86 lens[] are in the range 0..MAXBITS. The caller must assure this. 87 1..MAXBITS is interpreted as that code length. zero means that that 88 symbol does not occur in this code. 89 90 The codes are sorted by computing a count of codes for each length, 91 creating from that a table of starting indices for each length in the 92 sorted table, and then entering the symbols in order in the sorted 93 table. The sorted table is work[], with that space being provided by 94 the caller. 95 96 The length counts are used for other purposes as well, i.e. finding 97 the minimum and maximum length codes, determining if there are any 98 codes at all, checking for a valid set of lengths, and looking ahead 99 at length counts to determine sub-table sizes when building the 100 decoding tables. 101 */ 102 103 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ 104 for (len = 0; len <= MAXBITS; len++) 105 count[len] = 0; 106 for (sym = 0; sym < codes; sym++) 107 count[lens[sym]]++; 108 109 /* bound code lengths, force root to be within code lengths */ 110 root = *bits; 111 for (max = MAXBITS; max >= 1; max--) 112 if (count[max] != 0) break; 113 if (root > max) root = max; 114 if (max == 0) return -1; /* no codes! */ 115 for (min = 1; min <= MAXBITS; min++) 116 if (count[min] != 0) break; 117 if (root < min) root = min; 118 119 /* check for an over-subscribed or incomplete set of lengths */ 120 left = 1; 121 for (len = 1; len <= MAXBITS; len++) { 122 left <<= 1; 123 left -= count[len]; 124 if (left < 0) return -1; /* over-subscribed */ 125 } 126 if (left > 0 && (type == CODES || max != 1)) 127 return -1; /* incomplete set */ 128 129 /* generate offsets into symbol table for each length for sorting */ 130 offs[1] = 0; 131 for (len = 1; len < MAXBITS; len++) 132 offs[len + 1] = offs[len] + count[len]; 133 134 /* sort symbols by length, by symbol order within each length */ 135 for (sym = 0; sym < codes; sym++) 136 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; 137 138 /* 139 Create and fill in decoding tables. In this loop, the table being 140 filled is at next and has curr index bits. The code being used is huff 141 with length len. That code is converted to an index by dropping drop 142 bits off of the bottom. For codes where len is less than drop + curr, 143 those top drop + curr - len bits are incremented through all values to 144 fill the table with replicated entries. 145 146 root is the number of index bits for the root table. When len exceeds 147 root, sub-tables are created pointed to by the root entry with an index 148 of the low root bits of huff. This is saved in low to check for when a 149 new sub-table should be started. drop is zero when the root table is 150 being filled, and drop is root when sub-tables are being filled. 151 152 When a new sub-table is needed, it is necessary to look ahead in the 153 code lengths to determine what size sub-table is needed. The length 154 counts are used for this, and so count[] is decremented as codes are 155 entered in the tables. 156 157 used keeps track of how many table entries have been allocated from the 158 provided *table space. It is checked for LENS and DIST tables against 159 the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in 160 the initial root table size constants. See the comments in inftree9.h 161 for more information. 162 163 sym increments through all symbols, and the loop terminates when 164 all codes of length max, i.e. all codes, have been processed. This 165 routine permits incomplete codes, so another loop after this one fills 166 in the rest of the decoding tables with invalid code markers. 167 */ 168 169 /* set up for code type */ 170 switch (type) { 171 case CODES: 172 base = extra = work; /* dummy value--not used */ 173 end = 19; 174 break; 175 case LENS: 176 base = lbase; 177 base -= 257; 178 extra = lext; 179 extra -= 257; 180 end = 256; 181 break; 182 default: /* DISTS */ 183 base = dbase; 184 extra = dext; 185 end = -1; 186 } 187 188 /* initialize state for loop */ 189 huff = 0; /* starting code */ 190 sym = 0; /* starting code symbol */ 191 len = min; /* starting code length */ 192 next = *table; /* current table to fill in */ 193 curr = root; /* current table index bits */ 194 drop = 0; /* current bits to drop from code for index */ 195 low = (unsigned)(-1); /* trigger new sub-table when len > root */ 196 used = 1U << root; /* use root table entries */ 197 mask = used - 1; /* mask for comparing low */ 198 199 /* check available table space */ 200 if ((type == LENS && used >= ENOUGH_LENS) || 201 (type == DISTS && used >= ENOUGH_DISTS)) 202 return 1; 203 204 /* process all codes and make table entries */ 205 for (;;) { 206 /* create table entry */ 207 this.bits = (unsigned char)(len - drop); 208 if ((int)(work[sym]) < end) { 209 this.op = (unsigned char)0; 210 this.val = work[sym]; 211 } 212 else if ((int)(work[sym]) > end) { 213 this.op = (unsigned char)(extra[work[sym]]); 214 this.val = base[work[sym]]; 215 } 216 else { 217 this.op = (unsigned char)(32 + 64); /* end of block */ 218 this.val = 0; 219 } 220 221 /* replicate for those indices with low len bits equal to huff */ 222 incr = 1U << (len - drop); 223 fill = 1U << curr; 224 do { 225 fill -= incr; 226 next[(huff >> drop) + fill] = this; 227 } while (fill != 0); 228 229 /* backwards increment the len-bit code huff */ 230 incr = 1U << (len - 1); 231 while (huff & incr) 232 incr >>= 1; 233 if (incr != 0) { 234 huff &= incr - 1; 235 huff += incr; 236 } 237 else 238 huff = 0; 239 240 /* go to next symbol, update count, len */ 241 sym++; 242 if (--(count[len]) == 0) { 243 if (len == max) break; 244 len = lens[work[sym]]; 245 } 246 247 /* create new sub-table if needed */ 248 if (len > root && (huff & mask) != low) { 249 /* if first time, transition to sub-tables */ 250 if (drop == 0) 251 drop = root; 252 253 /* increment past last table */ 254 next += 1U << curr; 255 256 /* determine length of next table */ 257 curr = len - drop; 258 left = (int)(1 << curr); 259 while (curr + drop < max) { 260 left -= count[curr + drop]; 261 if (left <= 0) break; 262 curr++; 263 left <<= 1; 264 } 265 266 /* check for enough space */ 267 used += 1U << curr; 268 if ((type == LENS && used >= ENOUGH_LENS) || 269 (type == DISTS && used >= ENOUGH_DISTS)) 270 return 1; 271 272 /* point entry in root table to sub-table */ 273 low = huff & mask; 274 (*table)[low].op = (unsigned char)curr; 275 (*table)[low].bits = (unsigned char)root; 276 (*table)[low].val = (unsigned short)(next - *table); 277 } 278 } 279 280 /* 281 Fill in rest of table for incomplete codes. This loop is similar to the 282 loop above in incrementing huff for table indices. It is assumed that 283 len is equal to curr + drop, so there is no loop needed to increment 284 through high index bits. When the current sub-table is filled, the loop 285 drops back to the root table to fill in any remaining entries there. 286 */ 287 this.op = (unsigned char)64; /* invalid code marker */ 288 this.bits = (unsigned char)(len - drop); 289 this.val = (unsigned short)0; 290 while (huff != 0) { 291 /* when done with sub-table, drop back to root table */ 292 if (drop != 0 && (huff & mask) != low) { 293 drop = 0; 294 len = root; 295 next = *table; 296 curr = root; 297 this.bits = (unsigned char)len; 298 } 299 300 /* put invalid code marker in table */ 301 next[huff >> drop] = this; 302 303 /* backwards increment the len-bit code huff */ 304 incr = 1U << (len - 1); 305 while (huff & incr) 306 incr >>= 1; 307 if (incr != 0) { 308 huff &= incr - 1; 309 huff += incr; 310 } 311 else 312 huff = 0; 313 } 314 315 /* set return parameters */ 316 *table += used; 317 *bits = root; 318 return 0; 319} 320