1 /* inftrees.c -- generate Huffman trees for efficient decoding 2 * Copyright (C) 1995-2005 Mark Adler 3 * For conditions of distribution and use, see copyright notice in zlib.h 4 */ 5 6 #pragma ident "%Z%%M% %I% %E% SMI" 7 8 #include "zutil.h" 9 #include "inftrees.h" 10 11 #define MAXBITS 15 12 13 static const char inflate_copyright[] = 14 " inflate 1.2.3 Copyright 1995-2005 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 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 min, max; /* 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 this; /* 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 int end; /* use base and extra for symbol > end */ 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, 201, 196}; 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 (max = MAXBITS; max >= 1; max--) 117 if (count[max] != 0) break; 118 if (root > max) root = max; 119 if (max == 0) { /* no symbols to code at all */ 120 this.op = (unsigned char)64; /* invalid code marker */ 121 this.bits = (unsigned char)1; 122 this.val = (unsigned short)0; 123 *(*table)++ = this; /* make a table to force an error */ 124 *(*table)++ = this; 125 *bits = 1; 126 return 0; /* no symbols, but wait for decoding to report error */ 127 } 128 for (min = 1; min <= MAXBITS; min++) 129 if (count[min] != 0) break; 130 if (root < min) root = min; 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 || max != 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 when a LENS table is being made 172 against the space in *table, ENOUGH, minus the maximum space needed by 173 the worst case distance code, MAXD. This should never happen, but the 174 sufficiency of ENOUGH has not been proven exhaustively, hence the check. 175 This assumes that when type == LENS, bits == 9. 176 177 sym increments through all symbols, and the loop terminates when 178 all codes of length max, i.e. all codes, have been processed. This 179 routine permits incomplete codes, so another loop after this one fills 180 in the rest of the decoding tables with invalid code markers. 181 */ 182 183 /* set up for code type */ 184 switch (type) { 185 case CODES: 186 base = extra = work; /* dummy value--not used */ 187 end = 19; 188 break; 189 case LENS: 190 base = lbase; 191 base -= 257; 192 extra = lext; 193 extra -= 257; 194 end = 256; 195 break; 196 default: /* DISTS */ 197 base = dbase; 198 extra = dext; 199 end = -1; 200 } 201 202 /* initialize state for loop */ 203 huff = 0; /* starting code */ 204 sym = 0; /* starting code symbol */ 205 len = min; /* starting code length */ 206 next = *table; /* current table to fill in */ 207 curr = root; /* current table index bits */ 208 drop = 0; /* current bits to drop from code for index */ 209 low = (unsigned)(-1); /* trigger new sub-table when len > root */ 210 used = 1U << root; /* use root table entries */ 211 mask = used - 1; /* mask for comparing low */ 212 213 /* check available table space */ 214 if (type == LENS && used >= ENOUGH - MAXD) 215 return 1; 216 217 /* process all codes and make table entries */ 218 for (;;) { 219 /* create table entry */ 220 this.bits = (unsigned char)(len - drop); 221 if ((int)(work[sym]) < end) { 222 this.op = (unsigned char)0; 223 this.val = work[sym]; 224 } 225 else if ((int)(work[sym]) > end) { 226 this.op = (unsigned char)(extra[work[sym]]); 227 this.val = base[work[sym]]; 228 } 229 else { 230 this.op = (unsigned char)(32 + 64); /* end of block */ 231 this.val = 0; 232 } 233 234 /* replicate for those indices with low len bits equal to huff */ 235 incr = 1U << (len - drop); 236 fill = 1U << curr; 237 min = fill; /* save offset to next table */ 238 do { 239 fill -= incr; 240 next[(huff >> drop) + fill] = this; 241 } while (fill != 0); 242 243 /* backwards increment the len-bit code huff */ 244 incr = 1U << (len - 1); 245 while (huff & incr) 246 incr >>= 1; 247 if (incr != 0) { 248 huff &= incr - 1; 249 huff += incr; 250 } 251 else 252 huff = 0; 253 254 /* go to next symbol, update count, len */ 255 sym++; 256 if (--(count[len]) == 0) { 257 if (len == max) break; 258 len = lens[work[sym]]; 259 } 260 261 /* create new sub-table if needed */ 262 if (len > root && (huff & mask) != low) { 263 /* if first time, transition to sub-tables */ 264 if (drop == 0) 265 drop = root; 266 267 /* increment past last table */ 268 next += min; /* here min is 1 << curr */ 269 270 /* determine length of next table */ 271 curr = len - drop; 272 left = (int)(1 << curr); 273 while (curr + drop < max) { 274 left -= count[curr + drop]; 275 if (left <= 0) break; 276 curr++; 277 left <<= 1; 278 } 279 280 /* check for enough space */ 281 used += 1U << curr; 282 if (type == LENS && used >= ENOUGH - MAXD) 283 return 1; 284 285 /* point entry in root table to sub-table */ 286 low = huff & mask; 287 (*table)[low].op = (unsigned char)curr; 288 (*table)[low].bits = (unsigned char)root; 289 (*table)[low].val = (unsigned short)(next - *table); 290 } 291 } 292 293 /* 294 Fill in rest of table for incomplete codes. This loop is similar to the 295 loop above in incrementing huff for table indices. It is assumed that 296 len is equal to curr + drop, so there is no loop needed to increment 297 through high index bits. When the current sub-table is filled, the loop 298 drops back to the root table to fill in any remaining entries there. 299 */ 300 this.op = (unsigned char)64; /* invalid code marker */ 301 this.bits = (unsigned char)(len - drop); 302 this.val = (unsigned short)0; 303 while (huff != 0) { 304 /* when done with sub-table, drop back to root table */ 305 if (drop != 0 && (huff & mask) != low) { 306 drop = 0; 307 len = root; 308 next = *table; 309 this.bits = (unsigned char)len; 310 } 311 312 /* put invalid code marker in table */ 313 next[huff >> drop] = this; 314 315 /* backwards increment the len-bit code huff */ 316 incr = 1U << (len - 1); 317 while (huff & incr) 318 incr >>= 1; 319 if (incr != 0) { 320 huff &= incr - 1; 321 huff += incr; 322 } 323 else 324 huff = 0; 325 } 326 327 /* set return parameters */ 328 *table += used; 329 *bits = root; 330 return 0; 331 } 332