1 /* inftree9.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 #include "zutil.h" 7 #include "inftree9.h" 8 9 #define MAXBITS 15 10 11 const char inflate9_copyright[] = 12 " inflate9 1.2.3 Copyright 1995-2005 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 inflate_table9(type, lens, codes, table, bits, work) 33 codetype type; 34 unsigned short FAR *lens; 35 unsigned codes; 36 code FAR * FAR *table; 37 unsigned FAR *bits; 38 unsigned short FAR *work; 39 { 40 unsigned len; /* a code's length in bits */ 41 unsigned sym; /* index of code symbols */ 42 unsigned min, max; /* minimum and maximum code lengths */ 43 unsigned root; /* number of index bits for root table */ 44 unsigned curr; /* number of index bits for current table */ 45 unsigned drop; /* code bits to drop for sub-table */ 46 int left; /* number of prefix codes available */ 47 unsigned used; /* code entries in table used */ 48 unsigned huff; /* Huffman code */ 49 unsigned incr; /* for incrementing code, index */ 50 unsigned fill; /* index for replicating entries */ 51 unsigned low; /* low bits for current root entry */ 52 unsigned mask; /* mask for low root bits */ 53 code this; /* table entry for duplication */ 54 code FAR *next; /* next available space in table */ 55 const unsigned short FAR *base; /* base value table to use */ 56 const unsigned short FAR *extra; /* extra bits table to use */ 57 int end; /* use base and extra for symbol > end */ 58 unsigned short count[MAXBITS+1]; /* number of codes of each length */ 59 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ 60 static const unsigned short lbase[31] = { /* Length codes 257..285 base */ 61 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 62 19, 23, 27, 31, 35, 43, 51, 59, 67, 83, 99, 115, 63 131, 163, 195, 227, 3, 0, 0}; 64 static const unsigned short lext[31] = { /* Length codes 257..285 extra */ 65 128, 128, 128, 128, 128, 128, 128, 128, 129, 129, 129, 129, 66 130, 130, 130, 130, 131, 131, 131, 131, 132, 132, 132, 132, 67 133, 133, 133, 133, 144, 201, 196}; 68 static const unsigned short dbase[32] = { /* Distance codes 0..31 base */ 69 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 70 65, 97, 129, 193, 257, 385, 513, 769, 1025, 1537, 2049, 3073, 71 4097, 6145, 8193, 12289, 16385, 24577, 32769, 49153}; 72 static const unsigned short dext[32] = { /* Distance codes 0..31 extra */ 73 128, 128, 128, 128, 129, 129, 130, 130, 131, 131, 132, 132, 74 133, 133, 134, 134, 135, 135, 136, 136, 137, 137, 138, 138, 75 139, 139, 140, 140, 141, 141, 142, 142}; 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) return -1; /* no codes! */ 120 for (min = 1; min <= MAXBITS; min++) 121 if (count[min] != 0) break; 122 if (root < min) root = min; 123 124 /* check for an over-subscribed or incomplete set of lengths */ 125 left = 1; 126 for (len = 1; len <= MAXBITS; len++) { 127 left <<= 1; 128 left -= count[len]; 129 if (left < 0) return -1; /* over-subscribed */ 130 } 131 if (left > 0 && (type == CODES || max != 1)) 132 return -1; /* incomplete set */ 133 134 /* generate offsets into symbol table for each length for sorting */ 135 offs[1] = 0; 136 for (len = 1; len < MAXBITS; len++) 137 offs[len + 1] = offs[len] + count[len]; 138 139 /* sort symbols by length, by symbol order within each length */ 140 for (sym = 0; sym < codes; sym++) 141 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; 142 143 /* 144 Create and fill in decoding tables. In this loop, the table being 145 filled is at next and has curr index bits. The code being used is huff 146 with length len. That code is converted to an index by dropping drop 147 bits off of the bottom. For codes where len is less than drop + curr, 148 those top drop + curr - len bits are incremented through all values to 149 fill the table with replicated entries. 150 151 root is the number of index bits for the root table. When len exceeds 152 root, sub-tables are created pointed to by the root entry with an index 153 of the low root bits of huff. This is saved in low to check for when a 154 new sub-table should be started. drop is zero when the root table is 155 being filled, and drop is root when sub-tables are being filled. 156 157 When a new sub-table is needed, it is necessary to look ahead in the 158 code lengths to determine what size sub-table is needed. The length 159 counts are used for this, and so count[] is decremented as codes are 160 entered in the tables. 161 162 used keeps track of how many table entries have been allocated from the 163 provided *table space. It is checked when a LENS table is being made 164 against the space in *table, ENOUGH, minus the maximum space needed by 165 the worst case distance code, MAXD. This should never happen, but the 166 sufficiency of ENOUGH has not been proven exhaustively, hence the check. 167 This assumes that when type == LENS, bits == 9. 168 169 sym increments through all symbols, and the loop terminates when 170 all codes of length max, i.e. all codes, have been processed. This 171 routine permits incomplete codes, so another loop after this one fills 172 in the rest of the decoding tables with invalid code markers. 173 */ 174 175 /* set up for code type */ 176 switch (type) { 177 case CODES: 178 base = extra = work; /* dummy value--not used */ 179 end = 19; 180 break; 181 case LENS: 182 base = lbase; 183 base -= 257; 184 extra = lext; 185 extra -= 257; 186 end = 256; 187 break; 188 default: /* DISTS */ 189 base = dbase; 190 extra = dext; 191 end = -1; 192 } 193 194 /* initialize state for loop */ 195 huff = 0; /* starting code */ 196 sym = 0; /* starting code symbol */ 197 len = min; /* starting code length */ 198 next = *table; /* current table to fill in */ 199 curr = root; /* current table index bits */ 200 drop = 0; /* current bits to drop from code for index */ 201 low = (unsigned)(-1); /* trigger new sub-table when len > root */ 202 used = 1U << root; /* use root table entries */ 203 mask = used - 1; /* mask for comparing low */ 204 205 /* check available table space */ 206 if (type == LENS && used >= ENOUGH - MAXD) 207 return 1; 208 209 /* process all codes and make table entries */ 210 for (;;) { 211 /* create table entry */ 212 this.bits = (unsigned char)(len - drop); 213 if ((int)(work[sym]) < end) { 214 this.op = (unsigned char)0; 215 this.val = work[sym]; 216 } 217 else if ((int)(work[sym]) > end) { 218 this.op = (unsigned char)(extra[work[sym]]); 219 this.val = base[work[sym]]; 220 } 221 else { 222 this.op = (unsigned char)(32 + 64); /* end of block */ 223 this.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 do { 230 fill -= incr; 231 next[(huff >> drop) + fill] = this; 232 } while (fill != 0); 233 234 /* backwards increment the len-bit code huff */ 235 incr = 1U << (len - 1); 236 while (huff & incr) 237 incr >>= 1; 238 if (incr != 0) { 239 huff &= incr - 1; 240 huff += incr; 241 } 242 else 243 huff = 0; 244 245 /* go to next symbol, update count, len */ 246 sym++; 247 if (--(count[len]) == 0) { 248 if (len == max) break; 249 len = lens[work[sym]]; 250 } 251 252 /* create new sub-table if needed */ 253 if (len > root && (huff & mask) != low) { 254 /* if first time, transition to sub-tables */ 255 if (drop == 0) 256 drop = root; 257 258 /* increment past last table */ 259 next += 1U << curr; 260 261 /* determine length of next table */ 262 curr = len - drop; 263 left = (int)(1 << curr); 264 while (curr + drop < max) { 265 left -= count[curr + drop]; 266 if (left <= 0) break; 267 curr++; 268 left <<= 1; 269 } 270 271 /* check for enough space */ 272 used += 1U << curr; 273 if (type == LENS && used >= ENOUGH - MAXD) 274 return 1; 275 276 /* point entry in root table to sub-table */ 277 low = huff & mask; 278 (*table)[low].op = (unsigned char)curr; 279 (*table)[low].bits = (unsigned char)root; 280 (*table)[low].val = (unsigned short)(next - *table); 281 } 282 } 283 284 /* 285 Fill in rest of table for incomplete codes. This loop is similar to the 286 loop above in incrementing huff for table indices. It is assumed that 287 len is equal to curr + drop, so there is no loop needed to increment 288 through high index bits. When the current sub-table is filled, the loop 289 drops back to the root table to fill in any remaining entries there. 290 */ 291 this.op = (unsigned char)64; /* invalid code marker */ 292 this.bits = (unsigned char)(len - drop); 293 this.val = (unsigned short)0; 294 while (huff != 0) { 295 /* when done with sub-table, drop back to root table */ 296 if (drop != 0 && (huff & mask) != low) { 297 drop = 0; 298 len = root; 299 next = *table; 300 curr = root; 301 this.bits = (unsigned char)len; 302 } 303 304 /* put invalid code marker in table */ 305 next[huff >> drop] = this; 306 307 /* backwards increment the len-bit code huff */ 308 incr = 1U << (len - 1); 309 while (huff & incr) 310 incr >>= 1; 311 if (incr != 0) { 312 huff &= incr - 1; 313 huff += incr; 314 } 315 else 316 huff = 0; 317 } 318 319 /* set return parameters */ 320 *table += used; 321 *bits = root; 322 return 0; 323 } 324
