inftrees.c revision 1.3.14.2
1 /* $NetBSD: inftrees.c,v 1.3.14.2 2020/04/21 19:37:36 martin Exp $ */ 2 3 /* inftrees.c -- generate Huffman trees for efficient decoding 4 * Copyright (C) 1995-2017 Mark Adler 5 * For conditions of distribution and use, see copyright notice in zlib.h 6 */ 7 8 #include "zutil.h" 9 #include "inftrees.h" 10 11 #define MAXBITS 15 12 13 const char inflate_copyright[] = 14 " inflate 1.2.10 Copyright 1995-2017 Mark Adler "; 15 /* 16 If you use the zlib library in a product, an acknowledgment is welcome 17 in the documentation of your product. If for some reason you cannot 18 include such an acknowledgment, I would appreciate that you keep this 19 copyright string in the executable of your product. 20 */ 21 22 /* 23 Build a set of tables to decode the provided canonical Huffman code. 24 The code lengths are lens[0..codes-1]. The result starts at *table, 25 whose indices are 0..2^bits-1. work is a writable array of at least 26 lens shorts, which is used as a work area. type is the type of code 27 to be generated, CODES, LENS, or DISTS. On return, zero is success, 28 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table 29 on return points to the next available entry's address. bits is the 30 requested root table index bits, and on return it is the actual root 31 table index bits. It will differ if the request is greater than the 32 longest code or if it is less than the shortest code. 33 */ 34 int ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work) 35 codetype type; 36 unsigned short FAR *lens; 37 unsigned codes; 38 code FAR * FAR *table; 39 unsigned FAR *bits; 40 unsigned short FAR *work; 41 { 42 unsigned len; /* a code's length in bits */ 43 unsigned sym; /* index of code symbols */ 44 unsigned mmin, mmax; /* minimum and maximum code lengths */ 45 unsigned root; /* number of index bits for root table */ 46 unsigned curr; /* number of index bits for current table */ 47 unsigned drop; /* code bits to drop for sub-table */ 48 int left; /* number of prefix codes available */ 49 unsigned used; /* code entries in table used */ 50 unsigned huff; /* Huffman code */ 51 unsigned incr; /* for incrementing code, index */ 52 unsigned fill; /* index for replicating entries */ 53 unsigned low; /* low bits for current root entry */ 54 unsigned mask; /* mask for low root bits */ 55 code here; /* table entry for duplication */ 56 code FAR *next; /* next available space in table */ 57 const unsigned short FAR *base; /* base value table to use */ 58 const unsigned short FAR *extra; /* extra bits table to use */ 59 unsigned match; /* use base and extra for symbol >= match */ 60 unsigned short count[MAXBITS+1]; /* number of codes of each length */ 61 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ 62 static const unsigned short lbase[31] = { /* Length codes 257..285 base */ 63 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 64 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0}; 65 static const unsigned short lext[31] = { /* Length codes 257..285 extra */ 66 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 67 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 192, 202}; 68 static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ 69 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 70 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 71 8193, 12289, 16385, 24577, 0, 0}; 72 static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ 73 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 74 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 75 28, 28, 29, 29, 64, 64}; 76 77 /* 78 Process a set of code lengths to create a canonical Huffman code. The 79 code lengths are lens[0..codes-1]. Each length corresponds to the 80 symbols 0..codes-1. The Huffman code is generated by first sorting the 81 symbols by length from short to long, and retaining the symbol order 82 for codes with equal lengths. Then the code starts with all zero bits 83 for the first code of the shortest length, and the codes are integer 84 increments for the same length, and zeros are appended as the length 85 increases. For the deflate format, these bits are stored backwards 86 from their more natural integer increment ordering, and so when the 87 decoding tables are built in the large loop below, the integer codes 88 are incremented backwards. 89 90 This routine assumes, but does not check, that all of the entries in 91 lens[] are in the range 0..MAXBITS. The caller must assure this. 92 1..MAXBITS is interpreted as that code length. zero means that that 93 symbol does not occur in this code. 94 95 The codes are sorted by computing a count of codes for each length, 96 creating from that a table of starting indices for each length in the 97 sorted table, and then entering the symbols in order in the sorted 98 table. The sorted table is work[], with that space being provided by 99 the caller. 100 101 The length counts are used for other purposes as well, i.e. finding 102 the minimum and maximum length codes, determining if there are any 103 codes at all, checking for a valid set of lengths, and looking ahead 104 at length counts to determine sub-table sizes when building the 105 decoding tables. 106 */ 107 108 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ 109 for (len = 0; len <= MAXBITS; len++) 110 count[len] = 0; 111 for (sym = 0; sym < codes; sym++) 112 count[lens[sym]]++; 113 114 /* bound code lengths, force root to be within code lengths */ 115 root = *bits; 116 for (mmax = MAXBITS; mmax >= 1; mmax--) 117 if (count[mmax] != 0) break; 118 if (root > mmax) root = mmax; 119 if (mmax == 0) { /* no symbols to code at all */ 120 here.op = (unsigned char)64; /* invalid code marker */ 121 here.bits = (unsigned char)1; 122 here.val = (unsigned short)0; 123 *(*table)++ = here; /* make a table to force an error */ 124 *(*table)++ = here; 125 *bits = 1; 126 return 0; /* no symbols, but wait for decoding to report error */ 127 } 128 for (mmin = 1; mmin <= MAXBITS; mmin++) 129 if (count[mmin] != 0) break; 130 if (root < mmin) root = mmin; 131 132 /* check for an over-subscribed or incomplete set of lengths */ 133 left = 1; 134 for (len = 1; len <= MAXBITS; len++) { 135 left <<= 1; 136 left -= count[len]; 137 if (left < 0) return -1; /* over-subscribed */ 138 } 139 if (left > 0 && (type == CODES || mmax != 1)) 140 return -1; /* incomplete set */ 141 142 /* generate offsets into symbol table for each length for sorting */ 143 offs[1] = 0; 144 for (len = 1; len < MAXBITS; len++) 145 offs[len + 1] = offs[len] + count[len]; 146 147 /* sort symbols by length, by symbol order within each length */ 148 for (sym = 0; sym < codes; sym++) 149 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; 150 151 /* 152 Create and fill in decoding tables. In this loop, the table being 153 filled is at next and has curr index bits. The code being used is huff 154 with length len. That code is converted to an index by dropping drop 155 bits off of the bottom. For codes where len is less than drop + curr, 156 those top drop + curr - len bits are incremented through all values to 157 fill the table with replicated entries. 158 159 root is the number of index bits for the root table. When len exceeds 160 root, sub-tables are created pointed to by the root entry with an index 161 of the low root bits of huff. This is saved in low to check for when a 162 new sub-table should be started. drop is zero when the root table is 163 being filled, and drop is root when sub-tables are being filled. 164 165 When a new sub-table is needed, it is necessary to look ahead in the 166 code lengths to determine what size sub-table is needed. The length 167 counts are used for this, and so count[] is decremented as codes are 168 entered in the tables. 169 170 used keeps track of how many table entries have been allocated from the 171 provided *table space. It is checked for LENS and DIST tables against 172 the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in 173 the initial root table size constants. See the comments in inftrees.h 174 for more information. 175 176 sym increments through all symbols, and the loop terminates when 177 all codes of length mmax, i.e. all codes, have been processed. This 178 routine permits incomplete codes, so another loop after this one fills 179 in the rest of the decoding tables with invalid code markers. 180 */ 181 182 /* set up for code type */ 183 switch (type) { 184 case CODES: 185 base = extra = work; /* dummy value--not used */ 186 match = 20; 187 break; 188 case LENS: 189 base = lbase; 190 extra = lext; 191 match = 257; 192 break; 193 default: /* DISTS */ 194 base = dbase; 195 extra = dext; 196 match = 0; 197 } 198 199 /* initialize state for loop */ 200 huff = 0; /* starting code */ 201 sym = 0; /* starting code symbol */ 202 len = mmin; /* starting code length */ 203 next = *table; /* current table to fill in */ 204 curr = root; /* current table index bits */ 205 drop = 0; /* current bits to drop from code for index */ 206 low = (unsigned)(-1); /* trigger new sub-table when len > root */ 207 used = 1U << root; /* use root table entries */ 208 mask = used - 1; /* mask for comparing low */ 209 210 /* check available table space */ 211 if ((type == LENS && used > ENOUGH_LENS) || 212 (type == DISTS && used > ENOUGH_DISTS)) 213 return 1; 214 215 /* process all codes and make table entries */ 216 for (;;) { 217 /* create table entry */ 218 here.bits = (unsigned char)(len - drop); 219 if (work[sym] + 1U < match) { 220 here.op = (unsigned char)0; 221 here.val = work[sym]; 222 } 223 else if (work[sym] >= match) { 224 here.op = (unsigned char)(extra[work[sym] - match]); 225 here.val = base[work[sym] - match]; 226 } 227 else { 228 here.op = (unsigned char)(32 + 64); /* end of block */ 229 here.val = 0; 230 } 231 232 /* replicate for those indices with low len bits equal to huff */ 233 incr = 1U << (len - drop); 234 fill = 1U << curr; 235 mmin = fill; /* save offset to next table */ 236 do { 237 fill -= incr; 238 next[(huff >> drop) + fill] = here; 239 } while (fill != 0); 240 241 /* backwards increment the len-bit code huff */ 242 incr = 1U << (len - 1); 243 while (huff & incr) 244 incr >>= 1; 245 if (incr != 0) { 246 huff &= incr - 1; 247 huff += incr; 248 } 249 else 250 huff = 0; 251 252 /* go to next symbol, update count, len */ 253 sym++; 254 if (--(count[len]) == 0) { 255 if (len == mmax) break; 256 len = lens[work[sym]]; 257 } 258 259 /* create new sub-table if needed */ 260 if (len > root && (huff & mask) != low) { 261 /* if first time, transition to sub-tables */ 262 if (drop == 0) 263 drop = root; 264 265 /* increment past last table */ 266 next += mmin; /* here mmin is 1 << curr */ 267 268 /* determine length of next table */ 269 curr = len - drop; 270 left = (int)(1 << curr); 271 while (curr + drop < mmax) { 272 left -= count[curr + drop]; 273 if (left <= 0) break; 274 curr++; 275 left <<= 1; 276 } 277 278 /* check for enough space */ 279 used += 1U << curr; 280 if ((type == LENS && used > ENOUGH_LENS) || 281 (type == DISTS && used > ENOUGH_DISTS)) 282 return 1; 283 284 /* point entry in root table to sub-table */ 285 low = huff & mask; 286 (*table)[low].op = (unsigned char)curr; 287 (*table)[low].bits = (unsigned char)root; 288 (*table)[low].val = (unsigned short)(next - *table); 289 } 290 } 291 292 /* fill in remaining table entry if code is incomplete (guaranteed to have 293 at most one remaining entry, since if the code is incomplete, the 294 maximum code length that was allowed to get this far is one bit) */ 295 if (huff != 0) { 296 here.op = (unsigned char)64; /* invalid code marker */ 297 here.bits = (unsigned char)(len - drop); 298 here.val = (unsigned short)0; 299 next[huff] = here; 300 } 301 302 /* set return parameters */ 303 *table += used; 304 *bits = root; 305 return 0; 306 } 307
Indexes created Mon Oct 13 00:09:54 GMT 2025