00001 /* inftree9.c -- generate Huffman trees for efficient decoding 00002 * Copyright (C) 1995-2010 Mark Adler 00003 * For conditions of distribution and use, see copyright notice in zlib.h 00004 */ 00005 00006 #include "zutil.h" 00007 #include "inftree9.h" 00008 00009 #define MAXBITS 15 00010 00011 const char inflate9_copyright[] = 00012 " inflate9 1.2.5 Copyright 1995-2010 Mark Adler "; 00013 /* 00014 If you use the zlib library in a product, an acknowledgment is welcome 00015 in the documentation of your product. If for some reason you cannot 00016 include such an acknowledgment, I would appreciate that you keep this 00017 copyright string in the executable of your product. 00018 */ 00019 00020 /* 00021 Build a set of tables to decode the provided canonical Huffman code. 00022 The code lengths are lens[0..codes-1]. The result starts at *table, 00023 whose indices are 0..2^bits-1. work is a writable array of at least 00024 lens shorts, which is used as a work area. type is the type of code 00025 to be generated, CODES, LENS, or DISTS. On return, zero is success, 00026 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table 00027 on return points to the next available entry's address. bits is the 00028 requested root table index bits, and on return it is the actual root 00029 table index bits. It will differ if the request is greater than the 00030 longest code or if it is less than the shortest code. 00031 */ 00032 int inflate_table9(type, lens, codes, table, bits, work) 00033 codetype type; 00034 unsigned short FAR *lens; 00035 unsigned codes; 00036 code FAR * FAR *table; 00037 unsigned FAR *bits; 00038 unsigned short FAR *work; 00039 { 00040 unsigned len; /* a code's length in bits */ 00041 unsigned sym; /* index of code symbols */ 00042 unsigned min, max; /* minimum and maximum code lengths */ 00043 unsigned root; /* number of index bits for root table */ 00044 unsigned curr; /* number of index bits for current table */ 00045 unsigned drop; /* code bits to drop for sub-table */ 00046 int left; /* number of prefix codes available */ 00047 unsigned used; /* code entries in table used */ 00048 unsigned huff; /* Huffman code */ 00049 unsigned incr; /* for incrementing code, index */ 00050 unsigned fill; /* index for replicating entries */ 00051 unsigned low; /* low bits for current root entry */ 00052 unsigned mask; /* mask for low root bits */ 00053 code this; /* table entry for duplication */ 00054 code FAR *next; /* next available space in table */ 00055 const unsigned short FAR *base; /* base value table to use */ 00056 const unsigned short FAR *extra; /* extra bits table to use */ 00057 int end; /* use base and extra for symbol > end */ 00058 unsigned short count[MAXBITS+1]; /* number of codes of each length */ 00059 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ 00060 static const unsigned short lbase[31] = { /* Length codes 257..285 base */ 00061 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 00062 19, 23, 27, 31, 35, 43, 51, 59, 67, 83, 99, 115, 00063 131, 163, 195, 227, 3, 0, 0}; 00064 static const unsigned short lext[31] = { /* Length codes 257..285 extra */ 00065 128, 128, 128, 128, 128, 128, 128, 128, 129, 129, 129, 129, 00066 130, 130, 130, 130, 131, 131, 131, 131, 132, 132, 132, 132, 00067 133, 133, 133, 133, 144, 73, 195}; 00068 static const unsigned short dbase[32] = { /* Distance codes 0..31 base */ 00069 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 00070 65, 97, 129, 193, 257, 385, 513, 769, 1025, 1537, 2049, 3073, 00071 4097, 6145, 8193, 12289, 16385, 24577, 32769, 49153}; 00072 static const unsigned short dext[32] = { /* Distance codes 0..31 extra */ 00073 128, 128, 128, 128, 129, 129, 130, 130, 131, 131, 132, 132, 00074 133, 133, 134, 134, 135, 135, 136, 136, 137, 137, 138, 138, 00075 139, 139, 140, 140, 141, 141, 142, 142}; 00076 00077 /* 00078 Process a set of code lengths to create a canonical Huffman code. The 00079 code lengths are lens[0..codes-1]. Each length corresponds to the 00080 symbols 0..codes-1. The Huffman code is generated by first sorting the 00081 symbols by length from short to long, and retaining the symbol order 00082 for codes with equal lengths. Then the code starts with all zero bits 00083 for the first code of the shortest length, and the codes are integer 00084 increments for the same length, and zeros are appended as the length 00085 increases. For the deflate format, these bits are stored backwards 00086 from their more natural integer increment ordering, and so when the 00087 decoding tables are built in the large loop below, the integer codes 00088 are incremented backwards. 00089 00090 This routine assumes, but does not check, that all of the entries in 00091 lens[] are in the range 0..MAXBITS. The caller must assure this. 00092 1..MAXBITS is interpreted as that code length. zero means that that 00093 symbol does not occur in this code. 00094 00095 The codes are sorted by computing a count of codes for each length, 00096 creating from that a table of starting indices for each length in the 00097 sorted table, and then entering the symbols in order in the sorted 00098 table. The sorted table is work[], with that space being provided by 00099 the caller. 00100 00101 The length counts are used for other purposes as well, i.e. finding 00102 the minimum and maximum length codes, determining if there are any 00103 codes at all, checking for a valid set of lengths, and looking ahead 00104 at length counts to determine sub-table sizes when building the 00105 decoding tables. 00106 */ 00107 00108 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ 00109 for (len = 0; len <= MAXBITS; len++) 00110 count[len] = 0; 00111 for (sym = 0; sym < codes; sym++) 00112 count[lens[sym]]++; 00113 00114 /* bound code lengths, force root to be within code lengths */ 00115 root = *bits; 00116 for (max = MAXBITS; max >= 1; max--) 00117 if (count[max] != 0) break; 00118 if (root > max) root = max; 00119 if (max == 0) return -1; /* no codes! */ 00120 for (min = 1; min <= MAXBITS; min++) 00121 if (count[min] != 0) break; 00122 if (root < min) root = min; 00123 00124 /* check for an over-subscribed or incomplete set of lengths */ 00125 left = 1; 00126 for (len = 1; len <= MAXBITS; len++) { 00127 left <<= 1; 00128 left -= count[len]; 00129 if (left < 0) return -1; /* over-subscribed */ 00130 } 00131 if (left > 0 && (type == CODES || max != 1)) 00132 return -1; /* incomplete set */ 00133 00134 /* generate offsets into symbol table for each length for sorting */ 00135 offs[1] = 0; 00136 for (len = 1; len < MAXBITS; len++) 00137 offs[len + 1] = offs[len] + count[len]; 00138 00139 /* sort symbols by length, by symbol order within each length */ 00140 for (sym = 0; sym < codes; sym++) 00141 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; 00142 00143 /* 00144 Create and fill in decoding tables. In this loop, the table being 00145 filled is at next and has curr index bits. The code being used is huff 00146 with length len. That code is converted to an index by dropping drop 00147 bits off of the bottom. For codes where len is less than drop + curr, 00148 those top drop + curr - len bits are incremented through all values to 00149 fill the table with replicated entries. 00150 00151 root is the number of index bits for the root table. When len exceeds 00152 root, sub-tables are created pointed to by the root entry with an index 00153 of the low root bits of huff. This is saved in low to check for when a 00154 new sub-table should be started. drop is zero when the root table is 00155 being filled, and drop is root when sub-tables are being filled. 00156 00157 When a new sub-table is needed, it is necessary to look ahead in the 00158 code lengths to determine what size sub-table is needed. The length 00159 counts are used for this, and so count[] is decremented as codes are 00160 entered in the tables. 00161 00162 used keeps track of how many table entries have been allocated from the 00163 provided *table space. It is checked for LENS and DIST tables against 00164 the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in 00165 the initial root table size constants. See the comments in inftree9.h 00166 for more information. 00167 00168 sym increments through all symbols, and the loop terminates when 00169 all codes of length max, i.e. all codes, have been processed. This 00170 routine permits incomplete codes, so another loop after this one fills 00171 in the rest of the decoding tables with invalid code markers. 00172 */ 00173 00174 /* set up for code type */ 00175 switch (type) { 00176 case CODES: 00177 base = extra = work; /* dummy value--not used */ 00178 end = 19; 00179 break; 00180 case LENS: 00181 base = lbase; 00182 base -= 257; 00183 extra = lext; 00184 extra -= 257; 00185 end = 256; 00186 break; 00187 default: /* DISTS */ 00188 base = dbase; 00189 extra = dext; 00190 end = -1; 00191 } 00192 00193 /* initialize state for loop */ 00194 huff = 0; /* starting code */ 00195 sym = 0; /* starting code symbol */ 00196 len = min; /* starting code length */ 00197 next = *table; /* current table to fill in */ 00198 curr = root; /* current table index bits */ 00199 drop = 0; /* current bits to drop from code for index */ 00200 low = (unsigned)(-1); /* trigger new sub-table when len > root */ 00201 used = 1U << root; /* use root table entries */ 00202 mask = used - 1; /* mask for comparing low */ 00203 00204 /* check available table space */ 00205 if ((type == LENS && used >= ENOUGH_LENS) || 00206 (type == DISTS && used >= ENOUGH_DISTS)) 00207 return 1; 00208 00209 /* process all codes and make table entries */ 00210 for (;;) { 00211 /* create table entry */ 00212 this.bits = (unsigned char)(len - drop); 00213 if ((int)(work[sym]) < end) { 00214 this.op = (unsigned char)0; 00215 this.val = work[sym]; 00216 } 00217 else if ((int)(work[sym]) > end) { 00218 this.op = (unsigned char)(extra[work[sym]]); 00219 this.val = base[work[sym]]; 00220 } 00221 else { 00222 this.op = (unsigned char)(32 + 64); /* end of block */ 00223 this.val = 0; 00224 } 00225 00226 /* replicate for those indices with low len bits equal to huff */ 00227 incr = 1U << (len - drop); 00228 fill = 1U << curr; 00229 do { 00230 fill -= incr; 00231 next[(huff >> drop) + fill] = this; 00232 } while (fill != 0); 00233 00234 /* backwards increment the len-bit code huff */ 00235 incr = 1U << (len - 1); 00236 while (huff & incr) 00237 incr >>= 1; 00238 if (incr != 0) { 00239 huff &= incr - 1; 00240 huff += incr; 00241 } 00242 else 00243 huff = 0; 00244 00245 /* go to next symbol, update count, len */ 00246 sym++; 00247 if (--(count[len]) == 0) { 00248 if (len == max) break; 00249 len = lens[work[sym]]; 00250 } 00251 00252 /* create new sub-table if needed */ 00253 if (len > root && (huff & mask) != low) { 00254 /* if first time, transition to sub-tables */ 00255 if (drop == 0) 00256 drop = root; 00257 00258 /* increment past last table */ 00259 next += 1U << curr; 00260 00261 /* determine length of next table */ 00262 curr = len - drop; 00263 left = (int)(1 << curr); 00264 while (curr + drop < max) { 00265 left -= count[curr + drop]; 00266 if (left <= 0) break; 00267 curr++; 00268 left <<= 1; 00269 } 00270 00271 /* check for enough space */ 00272 used += 1U << curr; 00273 if ((type == LENS && used >= ENOUGH_LENS) || 00274 (type == DISTS && used >= ENOUGH_DISTS)) 00275 return 1; 00276 00277 /* point entry in root table to sub-table */ 00278 low = huff & mask; 00279 (*table)[low].op = (unsigned char)curr; 00280 (*table)[low].bits = (unsigned char)root; 00281 (*table)[low].val = (unsigned short)(next - *table); 00282 } 00283 } 00284 00285 /* 00286 Fill in rest of table for incomplete codes. This loop is similar to the 00287 loop above in incrementing huff for table indices. It is assumed that 00288 len is equal to curr + drop, so there is no loop needed to increment 00289 through high index bits. When the current sub-table is filled, the loop 00290 drops back to the root table to fill in any remaining entries there. 00291 */ 00292 this.op = (unsigned char)64; /* invalid code marker */ 00293 this.bits = (unsigned char)(len - drop); 00294 this.val = (unsigned short)0; 00295 while (huff != 0) { 00296 /* when done with sub-table, drop back to root table */ 00297 if (drop != 0 && (huff & mask) != low) { 00298 drop = 0; 00299 len = root; 00300 next = *table; 00301 curr = root; 00302 this.bits = (unsigned char)len; 00303 } 00304 00305 /* put invalid code marker in table */ 00306 next[huff >> drop] = this; 00307 00308 /* backwards increment the len-bit code huff */ 00309 incr = 1U << (len - 1); 00310 while (huff & incr) 00311 incr >>= 1; 00312 if (incr != 0) { 00313 huff &= incr - 1; 00314 huff += incr; 00315 } 00316 else 00317 huff = 0; 00318 } 00319 00320 /* set return parameters */ 00321 *table += used; 00322 *bits = root; 00323 return 0; 00324 }