1168404Spjd/* inftrees.c -- generate Huffman trees for efficient decoding 2168404Spjd * Copyright (C) 1995-2005 Mark Adler 3168404Spjd * For conditions of distribution and use, see copyright notice in zlib.h 4168404Spjd */ 5168404Spjd 6168404Spjd#pragma ident "%Z%%M% %I% %E% SMI" 7168404Spjd 8168404Spjd#include "zutil.h" 9168404Spjd#include "inftrees.h" 10168404Spjd 11168404Spjd#define MAXBITS 15 12168404Spjd 13168404Spjdstatic const char inflate_copyright[] = 14168404Spjd " inflate 1.2.3 Copyright 1995-2005 Mark Adler "; 15168404Spjd/* 16168404Spjd If you use the zlib library in a product, an acknowledgment is welcome 17168404Spjd in the documentation of your product. If for some reason you cannot 18168404Spjd include such an acknowledgment, I would appreciate that you keep this 19168404Spjd copyright string in the executable of your product. 20168404Spjd */ 21168404Spjd 22168404Spjd/* 23168404Spjd Build a set of tables to decode the provided canonical Huffman code. 24168404Spjd The code lengths are lens[0..codes-1]. The result starts at *table, 25168404Spjd whose indices are 0..2^bits-1. work is a writable array of at least 26168404Spjd lens shorts, which is used as a work area. type is the type of code 27168404Spjd to be generated, CODES, LENS, or DISTS. On return, zero is success, 28168404Spjd -1 is an invalid code, and +1 means that ENOUGH isn't enough. table 29168404Spjd on return points to the next available entry's address. bits is the 30168404Spjd requested root table index bits, and on return it is the actual root 31168404Spjd table index bits. It will differ if the request is greater than the 32168404Spjd longest code or if it is less than the shortest code. 33168404Spjd */ 34168404Spjdint inflate_table(type, lens, codes, table, bits, work) 35168404Spjdcodetype type; 36168404Spjdunsigned short FAR *lens; 37168404Spjdunsigned codes; 38168404Spjdcode FAR * FAR *table; 39168404Spjdunsigned FAR *bits; 40168404Spjdunsigned short FAR *work; 41168404Spjd{ 42168404Spjd unsigned len; /* a code's length in bits */ 43168404Spjd unsigned sym; /* index of code symbols */ 44168404Spjd unsigned min, max; /* minimum and maximum code lengths */ 45168404Spjd unsigned root; /* number of index bits for root table */ 46168404Spjd unsigned curr; /* number of index bits for current table */ 47168404Spjd unsigned drop; /* code bits to drop for sub-table */ 48168404Spjd int left; /* number of prefix codes available */ 49168404Spjd unsigned used; /* code entries in table used */ 50168404Spjd unsigned huff; /* Huffman code */ 51168404Spjd unsigned incr; /* for incrementing code, index */ 52168404Spjd unsigned fill; /* index for replicating entries */ 53168404Spjd unsigned low; /* low bits for current root entry */ 54168404Spjd unsigned mask; /* mask for low root bits */ 55168404Spjd code this; /* table entry for duplication */ 56168404Spjd code FAR *next; /* next available space in table */ 57168404Spjd const unsigned short FAR *base; /* base value table to use */ 58168404Spjd const unsigned short FAR *extra; /* extra bits table to use */ 59168404Spjd int end; /* use base and extra for symbol > end */ 60168404Spjd unsigned short count[MAXBITS+1]; /* number of codes of each length */ 61168404Spjd unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ 62168404Spjd static const unsigned short lbase[31] = { /* Length codes 257..285 base */ 63168404Spjd 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 64168404Spjd 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0}; 65168404Spjd static const unsigned short lext[31] = { /* Length codes 257..285 extra */ 66168404Spjd 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 67168404Spjd 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 201, 196}; 68168404Spjd static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ 69168404Spjd 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 70168404Spjd 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 71168404Spjd 8193, 12289, 16385, 24577, 0, 0}; 72168404Spjd static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ 73168404Spjd 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 74168404Spjd 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 75168404Spjd 28, 28, 29, 29, 64, 64}; 76168404Spjd 77168404Spjd /* 78168404Spjd Process a set of code lengths to create a canonical Huffman code. The 79168404Spjd code lengths are lens[0..codes-1]. Each length corresponds to the 80168404Spjd symbols 0..codes-1. The Huffman code is generated by first sorting the 81168404Spjd symbols by length from short to long, and retaining the symbol order 82168404Spjd for codes with equal lengths. Then the code starts with all zero bits 83168404Spjd for the first code of the shortest length, and the codes are integer 84168404Spjd increments for the same length, and zeros are appended as the length 85168404Spjd increases. For the deflate format, these bits are stored backwards 86168404Spjd from their more natural integer increment ordering, and so when the 87168404Spjd decoding tables are built in the large loop below, the integer codes 88168404Spjd are incremented backwards. 89168404Spjd 90168404Spjd This routine assumes, but does not check, that all of the entries in 91168404Spjd lens[] are in the range 0..MAXBITS. The caller must assure this. 92168404Spjd 1..MAXBITS is interpreted as that code length. zero means that that 93168404Spjd symbol does not occur in this code. 94168404Spjd 95168404Spjd The codes are sorted by computing a count of codes for each length, 96168404Spjd creating from that a table of starting indices for each length in the 97168404Spjd sorted table, and then entering the symbols in order in the sorted 98168404Spjd table. The sorted table is work[], with that space being provided by 99168404Spjd the caller. 100168404Spjd 101168404Spjd The length counts are used for other purposes as well, i.e. finding 102168404Spjd the minimum and maximum length codes, determining if there are any 103168404Spjd codes at all, checking for a valid set of lengths, and looking ahead 104168404Spjd at length counts to determine sub-table sizes when building the 105168404Spjd decoding tables. 106168404Spjd */ 107168404Spjd 108168404Spjd /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ 109168404Spjd for (len = 0; len <= MAXBITS; len++) 110168404Spjd count[len] = 0; 111168404Spjd for (sym = 0; sym < codes; sym++) 112168404Spjd count[lens[sym]]++; 113168404Spjd 114168404Spjd /* bound code lengths, force root to be within code lengths */ 115168404Spjd root = *bits; 116168404Spjd for (max = MAXBITS; max >= 1; max--) 117168404Spjd if (count[max] != 0) break; 118168404Spjd if (root > max) root = max; 119168404Spjd if (max == 0) { /* no symbols to code at all */ 120168404Spjd this.op = (unsigned char)64; /* invalid code marker */ 121168404Spjd this.bits = (unsigned char)1; 122168404Spjd this.val = (unsigned short)0; 123168404Spjd *(*table)++ = this; /* make a table to force an error */ 124168404Spjd *(*table)++ = this; 125168404Spjd *bits = 1; 126168404Spjd return 0; /* no symbols, but wait for decoding to report error */ 127168404Spjd } 128168404Spjd for (min = 1; min <= MAXBITS; min++) 129168404Spjd if (count[min] != 0) break; 130168404Spjd if (root < min) root = min; 131168404Spjd 132168404Spjd /* check for an over-subscribed or incomplete set of lengths */ 133168404Spjd left = 1; 134168404Spjd for (len = 1; len <= MAXBITS; len++) { 135168404Spjd left <<= 1; 136168404Spjd left -= count[len]; 137168404Spjd if (left < 0) return -1; /* over-subscribed */ 138168404Spjd } 139168404Spjd if (left > 0 && (type == CODES || max != 1)) 140168404Spjd return -1; /* incomplete set */ 141168404Spjd 142168404Spjd /* generate offsets into symbol table for each length for sorting */ 143168404Spjd offs[1] = 0; 144168404Spjd for (len = 1; len < MAXBITS; len++) 145168404Spjd offs[len + 1] = offs[len] + count[len]; 146168404Spjd 147168404Spjd /* sort symbols by length, by symbol order within each length */ 148168404Spjd for (sym = 0; sym < codes; sym++) 149168404Spjd if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; 150168404Spjd 151168404Spjd /* 152168404Spjd Create and fill in decoding tables. In this loop, the table being 153168404Spjd filled is at next and has curr index bits. The code being used is huff 154168404Spjd with length len. That code is converted to an index by dropping drop 155168404Spjd bits off of the bottom. For codes where len is less than drop + curr, 156168404Spjd those top drop + curr - len bits are incremented through all values to 157168404Spjd fill the table with replicated entries. 158168404Spjd 159168404Spjd root is the number of index bits for the root table. When len exceeds 160168404Spjd root, sub-tables are created pointed to by the root entry with an index 161168404Spjd of the low root bits of huff. This is saved in low to check for when a 162168404Spjd new sub-table should be started. drop is zero when the root table is 163168404Spjd being filled, and drop is root when sub-tables are being filled. 164168404Spjd 165168404Spjd When a new sub-table is needed, it is necessary to look ahead in the 166168404Spjd code lengths to determine what size sub-table is needed. The length 167168404Spjd counts are used for this, and so count[] is decremented as codes are 168168404Spjd entered in the tables. 169168404Spjd 170168404Spjd used keeps track of how many table entries have been allocated from the 171168404Spjd provided *table space. It is checked when a LENS table is being made 172168404Spjd against the space in *table, ENOUGH, minus the maximum space needed by 173168404Spjd the worst case distance code, MAXD. This should never happen, but the 174168404Spjd sufficiency of ENOUGH has not been proven exhaustively, hence the check. 175168404Spjd This assumes that when type == LENS, bits == 9. 176168404Spjd 177168404Spjd sym increments through all symbols, and the loop terminates when 178168404Spjd all codes of length max, i.e. all codes, have been processed. This 179168404Spjd routine permits incomplete codes, so another loop after this one fills 180168404Spjd in the rest of the decoding tables with invalid code markers. 181168404Spjd */ 182168404Spjd 183168404Spjd /* set up for code type */ 184168404Spjd switch (type) { 185168404Spjd case CODES: 186168404Spjd base = extra = work; /* dummy value--not used */ 187168404Spjd end = 19; 188168404Spjd break; 189168404Spjd case LENS: 190168404Spjd base = lbase; 191168404Spjd base -= 257; 192168404Spjd extra = lext; 193168404Spjd extra -= 257; 194168404Spjd end = 256; 195168404Spjd break; 196168404Spjd default: /* DISTS */ 197168404Spjd base = dbase; 198168404Spjd extra = dext; 199168404Spjd end = -1; 200168404Spjd } 201168404Spjd 202168404Spjd /* initialize state for loop */ 203168404Spjd huff = 0; /* starting code */ 204168404Spjd sym = 0; /* starting code symbol */ 205168404Spjd len = min; /* starting code length */ 206168404Spjd next = *table; /* current table to fill in */ 207168404Spjd curr = root; /* current table index bits */ 208168404Spjd drop = 0; /* current bits to drop from code for index */ 209168404Spjd low = (unsigned)(-1); /* trigger new sub-table when len > root */ 210168404Spjd used = 1U << root; /* use root table entries */ 211168404Spjd mask = used - 1; /* mask for comparing low */ 212168404Spjd 213168404Spjd /* check available table space */ 214168404Spjd if (type == LENS && used >= ENOUGH - MAXD) 215168404Spjd return 1; 216168404Spjd 217168404Spjd /* process all codes and make table entries */ 218168404Spjd for (;;) { 219168404Spjd /* create table entry */ 220168404Spjd this.bits = (unsigned char)(len - drop); 221168404Spjd if ((int)(work[sym]) < end) { 222168404Spjd this.op = (unsigned char)0; 223168404Spjd this.val = work[sym]; 224168404Spjd } 225168404Spjd else if ((int)(work[sym]) > end) { 226168404Spjd this.op = (unsigned char)(extra[work[sym]]); 227168404Spjd this.val = base[work[sym]]; 228168404Spjd } 229168404Spjd else { 230168404Spjd this.op = (unsigned char)(32 + 64); /* end of block */ 231168404Spjd this.val = 0; 232168404Spjd } 233168404Spjd 234168404Spjd /* replicate for those indices with low len bits equal to huff */ 235168404Spjd incr = 1U << (len - drop); 236168404Spjd fill = 1U << curr; 237168404Spjd min = fill; /* save offset to next table */ 238168404Spjd do { 239168404Spjd fill -= incr; 240168404Spjd next[(huff >> drop) + fill] = this; 241168404Spjd } while (fill != 0); 242168404Spjd 243168404Spjd /* backwards increment the len-bit code huff */ 244168404Spjd incr = 1U << (len - 1); 245168404Spjd while (huff & incr) 246168404Spjd incr >>= 1; 247168404Spjd if (incr != 0) { 248168404Spjd huff &= incr - 1; 249168404Spjd huff += incr; 250168404Spjd } 251168404Spjd else 252168404Spjd huff = 0; 253168404Spjd 254168404Spjd /* go to next symbol, update count, len */ 255168404Spjd sym++; 256168404Spjd if (--(count[len]) == 0) { 257168404Spjd if (len == max) break; 258168404Spjd len = lens[work[sym]]; 259168404Spjd } 260168404Spjd 261168404Spjd /* create new sub-table if needed */ 262168404Spjd if (len > root && (huff & mask) != low) { 263168404Spjd /* if first time, transition to sub-tables */ 264168404Spjd if (drop == 0) 265168404Spjd drop = root; 266168404Spjd 267168404Spjd /* increment past last table */ 268168404Spjd next += min; /* here min is 1 << curr */ 269168404Spjd 270168404Spjd /* determine length of next table */ 271168404Spjd curr = len - drop; 272168404Spjd left = (int)(1 << curr); 273168404Spjd while (curr + drop < max) { 274168404Spjd left -= count[curr + drop]; 275168404Spjd if (left <= 0) break; 276168404Spjd curr++; 277168404Spjd left <<= 1; 278168404Spjd } 279168404Spjd 280168404Spjd /* check for enough space */ 281168404Spjd used += 1U << curr; 282168404Spjd if (type == LENS && used >= ENOUGH - MAXD) 283168404Spjd return 1; 284168404Spjd 285168404Spjd /* point entry in root table to sub-table */ 286168404Spjd low = huff & mask; 287168404Spjd (*table)[low].op = (unsigned char)curr; 288168404Spjd (*table)[low].bits = (unsigned char)root; 289168404Spjd (*table)[low].val = (unsigned short)(next - *table); 290168404Spjd } 291168404Spjd } 292168404Spjd 293168404Spjd /* 294168404Spjd Fill in rest of table for incomplete codes. This loop is similar to the 295168404Spjd loop above in incrementing huff for table indices. It is assumed that 296168404Spjd len is equal to curr + drop, so there is no loop needed to increment 297168404Spjd through high index bits. When the current sub-table is filled, the loop 298168404Spjd drops back to the root table to fill in any remaining entries there. 299168404Spjd */ 300168404Spjd this.op = (unsigned char)64; /* invalid code marker */ 301168404Spjd this.bits = (unsigned char)(len - drop); 302168404Spjd this.val = (unsigned short)0; 303168404Spjd while (huff != 0) { 304168404Spjd /* when done with sub-table, drop back to root table */ 305168404Spjd if (drop != 0 && (huff & mask) != low) { 306168404Spjd drop = 0; 307168404Spjd len = root; 308168404Spjd next = *table; 309168404Spjd this.bits = (unsigned char)len; 310168404Spjd } 311168404Spjd 312168404Spjd /* put invalid code marker in table */ 313168404Spjd next[huff >> drop] = this; 314168404Spjd 315168404Spjd /* backwards increment the len-bit code huff */ 316168404Spjd incr = 1U << (len - 1); 317168404Spjd while (huff & incr) 318168404Spjd incr >>= 1; 319168404Spjd if (incr != 0) { 320168404Spjd huff &= incr - 1; 321168404Spjd huff += incr; 322168404Spjd } 323168404Spjd else 324168404Spjd huff = 0; 325168404Spjd } 326168404Spjd 327168404Spjd /* set return parameters */ 328168404Spjd *table += used; 329168404Spjd *bits = root; 330168404Spjd return 0; 331168404Spjd} 332