File indexing completed on 2024-04-21 03:48:32
0001 /* inftrees.c -- generate Huffman trees for efficient decoding 0002 * Copyright (C) 1995-2013 Mark Adler 0003 * For conditions of distribution and use, see copyright notice in zlib.h 0004 */ 0005 0006 #include "zutil.h" 0007 #include "inftrees.h" 0008 0009 #define MAXBITS 15 0010 0011 const char inflate_copyright[] = 0012 " inflate 1.2.8 Copyright 1995-2013 Mark Adler "; 0013 /* 0014 If you use the zlib library in a product, an acknowledgment is welcome 0015 in the documentation of your product. If for some reason you cannot 0016 include such an acknowledgment, I would appreciate that you keep this 0017 copyright string in the executable of your product. 0018 */ 0019 0020 /* 0021 Build a set of tables to decode the provided canonical Huffman code. 0022 The code lengths are lens[0..codes-1]. The result starts at *table, 0023 whose indices are 0..2^bits-1. work is a writable array of at least 0024 lens shorts, which is used as a work area. type is the type of code 0025 to be generated, CODES, LENS, or DISTS. On return, zero is success, 0026 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table 0027 on return points to the next available entry's address. bits is the 0028 requested root table index bits, and on return it is the actual root 0029 table index bits. It will differ if the request is greater than the 0030 longest code or if it is less than the shortest code. 0031 */ 0032 int ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work) 0033 codetype type; 0034 unsigned short FAR *lens; 0035 unsigned codes; 0036 code FAR * FAR *table; 0037 unsigned FAR *bits; 0038 unsigned short FAR *work; 0039 { 0040 unsigned len; /* a code's length in bits */ 0041 unsigned sym; /* index of code symbols */ 0042 unsigned min, max; /* minimum and maximum code lengths */ 0043 unsigned root; /* number of index bits for root table */ 0044 unsigned curr; /* number of index bits for current table */ 0045 unsigned drop; /* code bits to drop for sub-table */ 0046 int left; /* number of prefix codes available */ 0047 unsigned used; /* code entries in table used */ 0048 unsigned huff; /* Huffman code */ 0049 unsigned incr; /* for incrementing code, index */ 0050 unsigned fill; /* index for replicating entries */ 0051 unsigned low; /* low bits for current root entry */ 0052 unsigned mask; /* mask for low root bits */ 0053 code here; /* table entry for duplication */ 0054 code FAR *next; /* next available space in table */ 0055 const unsigned short FAR *base; /* base value table to use */ 0056 const unsigned short FAR *extra; /* extra bits table to use */ 0057 int end; /* use base and extra for symbol > end */ 0058 unsigned short count[MAXBITS+1]; /* number of codes of each length */ 0059 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ 0060 static const unsigned short lbase[31] = { /* Length codes 257..285 base */ 0061 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 0062 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0}; 0063 static const unsigned short lext[31] = { /* Length codes 257..285 extra */ 0064 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 0065 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 72, 78}; 0066 static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ 0067 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 0068 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 0069 8193, 12289, 16385, 24577, 0, 0}; 0070 static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ 0071 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 0072 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 0073 28, 28, 29, 29, 64, 64}; 0074 0075 /* 0076 Process a set of code lengths to create a canonical Huffman code. The 0077 code lengths are lens[0..codes-1]. Each length corresponds to the 0078 symbols 0..codes-1. The Huffman code is generated by first sorting the 0079 symbols by length from short to long, and retaining the symbol order 0080 for codes with equal lengths. Then the code starts with all zero bits 0081 for the first code of the shortest length, and the codes are integer 0082 increments for the same length, and zeros are appended as the length 0083 increases. For the deflate format, these bits are stored backwards 0084 from their more natural integer increment ordering, and so when the 0085 decoding tables are built in the large loop below, the integer codes 0086 are incremented backwards. 0087 0088 This routine assumes, but does not check, that all of the entries in 0089 lens[] are in the range 0..MAXBITS. The caller must assure this. 0090 1..MAXBITS is interpreted as that code length. zero means that that 0091 symbol does not occur in this code. 0092 0093 The codes are sorted by computing a count of codes for each length, 0094 creating from that a table of starting indices for each length in the 0095 sorted table, and then entering the symbols in order in the sorted 0096 table. The sorted table is work[], with that space being provided by 0097 the caller. 0098 0099 The length counts are used for other purposes as well, i.e. finding 0100 the minimum and maximum length codes, determining if there are any 0101 codes at all, checking for a valid set of lengths, and looking ahead 0102 at length counts to determine sub-table sizes when building the 0103 decoding tables. 0104 */ 0105 0106 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ 0107 for (len = 0; len <= MAXBITS; len++) 0108 count[len] = 0; 0109 for (sym = 0; sym < codes; sym++) 0110 count[lens[sym]]++; 0111 0112 /* bound code lengths, force root to be within code lengths */ 0113 root = *bits; 0114 for (max = MAXBITS; max >= 1; max--) 0115 if (count[max] != 0) break; 0116 if (root > max) root = max; 0117 if (max == 0) { /* no symbols to code at all */ 0118 here.op = (unsigned char)64; /* invalid code marker */ 0119 here.bits = (unsigned char)1; 0120 here.val = (unsigned short)0; 0121 *(*table)++ = here; /* make a table to force an error */ 0122 *(*table)++ = here; 0123 *bits = 1; 0124 return 0; /* no symbols, but wait for decoding to report error */ 0125 } 0126 for (min = 1; min < max; min++) 0127 if (count[min] != 0) break; 0128 if (root < min) root = min; 0129 0130 /* check for an over-subscribed or incomplete set of lengths */ 0131 left = 1; 0132 for (len = 1; len <= MAXBITS; len++) { 0133 left <<= 1; 0134 left -= count[len]; 0135 if (left < 0) return -1; /* over-subscribed */ 0136 } 0137 if (left > 0 && (type == CODES || max != 1)) 0138 return -1; /* incomplete set */ 0139 0140 /* generate offsets into symbol table for each length for sorting */ 0141 offs[1] = 0; 0142 for (len = 1; len < MAXBITS; len++) 0143 offs[len + 1] = offs[len] + count[len]; 0144 0145 /* sort symbols by length, by symbol order within each length */ 0146 for (sym = 0; sym < codes; sym++) 0147 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; 0148 0149 /* 0150 Create and fill in decoding tables. In this loop, the table being 0151 filled is at next and has curr index bits. The code being used is huff 0152 with length len. That code is converted to an index by dropping drop 0153 bits off of the bottom. For codes where len is less than drop + curr, 0154 those top drop + curr - len bits are incremented through all values to 0155 fill the table with replicated entries. 0156 0157 root is the number of index bits for the root table. When len exceeds 0158 root, sub-tables are created pointed to by the root entry with an index 0159 of the low root bits of huff. This is saved in low to check for when a 0160 new sub-table should be started. drop is zero when the root table is 0161 being filled, and drop is root when sub-tables are being filled. 0162 0163 When a new sub-table is needed, it is necessary to look ahead in the 0164 code lengths to determine what size sub-table is needed. The length 0165 counts are used for this, and so count[] is decremented as codes are 0166 entered in the tables. 0167 0168 used keeps track of how many table entries have been allocated from the 0169 provided *table space. It is checked for LENS and DIST tables against 0170 the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in 0171 the initial root table size constants. See the comments in inftrees.h 0172 for more information. 0173 0174 sym increments through all symbols, and the loop terminates when 0175 all codes of length max, i.e. all codes, have been processed. This 0176 routine permits incomplete codes, so another loop after this one fills 0177 in the rest of the decoding tables with invalid code markers. 0178 */ 0179 0180 /* set up for code type */ 0181 switch (type) { 0182 case CODES: 0183 base = extra = work; /* dummy value--not used */ 0184 end = 19; 0185 break; 0186 case LENS: 0187 base = lbase; 0188 base -= 257; 0189 extra = lext; 0190 extra -= 257; 0191 end = 256; 0192 break; 0193 default: /* DISTS */ 0194 base = dbase; 0195 extra = dext; 0196 end = -1; 0197 } 0198 0199 /* initialize state for loop */ 0200 huff = 0; /* starting code */ 0201 sym = 0; /* starting code symbol */ 0202 len = min; /* starting code length */ 0203 next = *table; /* current table to fill in */ 0204 curr = root; /* current table index bits */ 0205 drop = 0; /* current bits to drop from code for index */ 0206 low = (unsigned)(-1); /* trigger new sub-table when len > root */ 0207 used = 1U << root; /* use root table entries */ 0208 mask = used - 1; /* mask for comparing low */ 0209 0210 /* check available table space */ 0211 if ((type == LENS && used > ENOUGH_LENS) || 0212 (type == DISTS && used > ENOUGH_DISTS)) 0213 return 1; 0214 0215 /* process all codes and make table entries */ 0216 for (;;) { 0217 /* create table entry */ 0218 here.bits = (unsigned char)(len - drop); 0219 if ((int)(work[sym]) < end) { 0220 here.op = (unsigned char)0; 0221 here.val = work[sym]; 0222 } 0223 else if ((int)(work[sym]) > end) { 0224 here.op = (unsigned char)(extra[work[sym]]); 0225 here.val = base[work[sym]]; 0226 } 0227 else { 0228 here.op = (unsigned char)(32 + 64); /* end of block */ 0229 here.val = 0; 0230 } 0231 0232 /* replicate for those indices with low len bits equal to huff */ 0233 incr = 1U << (len - drop); 0234 fill = 1U << curr; 0235 min = fill; /* save offset to next table */ 0236 do { 0237 fill -= incr; 0238 next[(huff >> drop) + fill] = here; 0239 } while (fill != 0); 0240 0241 /* backwards increment the len-bit code huff */ 0242 incr = 1U << (len - 1); 0243 while (huff & incr) 0244 incr >>= 1; 0245 if (incr != 0) { 0246 huff &= incr - 1; 0247 huff += incr; 0248 } 0249 else 0250 huff = 0; 0251 0252 /* go to next symbol, update count, len */ 0253 sym++; 0254 if (--(count[len]) == 0) { 0255 if (len == max) break; 0256 len = lens[work[sym]]; 0257 } 0258 0259 /* create new sub-table if needed */ 0260 if (len > root && (huff & mask) != low) { 0261 /* if first time, transition to sub-tables */ 0262 if (drop == 0) 0263 drop = root; 0264 0265 /* increment past last table */ 0266 next += min; /* here min is 1 << curr */ 0267 0268 /* determine length of next table */ 0269 curr = len - drop; 0270 left = (int)(1 << curr); 0271 while (curr + drop < max) { 0272 left -= count[curr + drop]; 0273 if (left <= 0) break; 0274 curr++; 0275 left <<= 1; 0276 } 0277 0278 /* check for enough space */ 0279 used += 1U << curr; 0280 if ((type == LENS && used > ENOUGH_LENS) || 0281 (type == DISTS && used > ENOUGH_DISTS)) 0282 return 1; 0283 0284 /* point entry in root table to sub-table */ 0285 low = huff & mask; 0286 (*table)[low].op = (unsigned char)curr; 0287 (*table)[low].bits = (unsigned char)root; 0288 (*table)[low].val = (unsigned short)(next - *table); 0289 } 0290 } 0291 0292 /* fill in remaining table entry if code is incomplete (guaranteed to have 0293 at most one remaining entry, since if the code is incomplete, the 0294 maximum code length that was allowed to get this far is one bit) */ 0295 if (huff != 0) { 0296 here.op = (unsigned char)64; /* invalid code marker */ 0297 here.bits = (unsigned char)(len - drop); 0298 here.val = (unsigned short)0; 0299 next[huff] = here; 0300 } 0301 0302 /* set return parameters */ 0303 *table += used; 0304 *bits = root; 0305 return 0; 0306 }