Annotation of sys/lib/libz/inftrees.c, Revision 1.1
1.1 ! nbrk 1: /* $OpenBSD: inftrees.c,v 1.14 2005/07/20 15:56:46 millert Exp $ */
! 2: /* inftrees.c -- generate Huffman trees for efficient decoding
! 3: * Copyright (C) 1995-2005 Mark Adler
! 4: * For conditions of distribution and use, see copyright notice in zlib.h
! 5: */
! 6:
! 7: #include "zutil.h"
! 8: #include "inftrees.h"
! 9:
! 10: #define MAXBITS 15
! 11:
! 12: const char inflate_copyright[] =
! 13: " inflate 1.2.3 Copyright 1995-2005 Mark Adler ";
! 14: /*
! 15: If you use the zlib library in a product, an acknowledgment is welcome
! 16: in the documentation of your product. If for some reason you cannot
! 17: include such an acknowledgment, I would appreciate that you keep this
! 18: copyright string in the executable of your product.
! 19: */
! 20:
! 21: /*
! 22: Build a set of tables to decode the provided canonical Huffman code.
! 23: The code lengths are lens[0..codes-1]. The result starts at *table,
! 24: whose indices are 0..2^bits-1. work is a writable array of at least
! 25: lens shorts, which is used as a work area. type is the type of code
! 26: to be generated, CODES, LENS, or DISTS. On return, zero is success,
! 27: -1 is an invalid code, and +1 means that ENOUGH isn't enough. table
! 28: on return points to the next available entry's address. bits is the
! 29: requested root table index bits, and on return it is the actual root
! 30: table index bits. It will differ if the request is greater than the
! 31: longest code or if it is less than the shortest code.
! 32: */
! 33: int inflate_table(type, lens, codes, table, bits, work)
! 34: codetype type;
! 35: unsigned short FAR *lens;
! 36: unsigned codes;
! 37: code FAR * FAR *table;
! 38: unsigned FAR *bits;
! 39: unsigned short FAR *work;
! 40: {
! 41: unsigned len; /* a code's length in bits */
! 42: unsigned sym; /* index of code symbols */
! 43: unsigned min, max; /* minimum and maximum code lengths */
! 44: unsigned root; /* number of index bits for root table */
! 45: unsigned curr; /* number of index bits for current table */
! 46: unsigned drop; /* code bits to drop for sub-table */
! 47: int left; /* number of prefix codes available */
! 48: unsigned used; /* code entries in table used */
! 49: unsigned huff; /* Huffman code */
! 50: unsigned incr; /* for incrementing code, index */
! 51: unsigned fill; /* index for replicating entries */
! 52: unsigned low; /* low bits for current root entry */
! 53: unsigned mask; /* mask for low root bits */
! 54: code this; /* table entry for duplication */
! 55: code FAR *next; /* next available space in table */
! 56: const unsigned short FAR *base; /* base value table to use */
! 57: const unsigned short FAR *extra; /* extra bits table to use */
! 58: int end; /* use base and extra for symbol > end */
! 59: unsigned short count[MAXBITS+1]; /* number of codes of each length */
! 60: unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
! 61: static const unsigned short lbase[31] = { /* Length codes 257..285 base */
! 62: 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
! 63: 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
! 64: static const unsigned short lext[31] = { /* Length codes 257..285 extra */
! 65: 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
! 66: 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 201, 196};
! 67: static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
! 68: 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
! 69: 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
! 70: 8193, 12289, 16385, 24577, 0, 0};
! 71: static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
! 72: 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
! 73: 23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
! 74: 28, 28, 29, 29, 64, 64};
! 75:
! 76: /*
! 77: Process a set of code lengths to create a canonical Huffman code. The
! 78: code lengths are lens[0..codes-1]. Each length corresponds to the
! 79: symbols 0..codes-1. The Huffman code is generated by first sorting the
! 80: symbols by length from short to long, and retaining the symbol order
! 81: for codes with equal lengths. Then the code starts with all zero bits
! 82: for the first code of the shortest length, and the codes are integer
! 83: increments for the same length, and zeros are appended as the length
! 84: increases. For the deflate format, these bits are stored backwards
! 85: from their more natural integer increment ordering, and so when the
! 86: decoding tables are built in the large loop below, the integer codes
! 87: are incremented backwards.
! 88:
! 89: This routine assumes, but does not check, that all of the entries in
! 90: lens[] are in the range 0..MAXBITS. The caller must assure this.
! 91: 1..MAXBITS is interpreted as that code length. zero means that that
! 92: symbol does not occur in this code.
! 93:
! 94: The codes are sorted by computing a count of codes for each length,
! 95: creating from that a table of starting indices for each length in the
! 96: sorted table, and then entering the symbols in order in the sorted
! 97: table. The sorted table is work[], with that space being provided by
! 98: the caller.
! 99:
! 100: The length counts are used for other purposes as well, i.e. finding
! 101: the minimum and maximum length codes, determining if there are any
! 102: codes at all, checking for a valid set of lengths, and looking ahead
! 103: at length counts to determine sub-table sizes when building the
! 104: decoding tables.
! 105: */
! 106:
! 107: /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
! 108: for (len = 0; len <= MAXBITS; len++)
! 109: count[len] = 0;
! 110: for (sym = 0; sym < codes; sym++)
! 111: count[lens[sym]]++;
! 112:
! 113: /* bound code lengths, force root to be within code lengths */
! 114: root = *bits;
! 115: for (max = MAXBITS; max >= 1; max--)
! 116: if (count[max] != 0) break;
! 117: if (root > max) root = max;
! 118: if (max == 0) { /* no symbols to code at all */
! 119: this.op = (unsigned char)64; /* invalid code marker */
! 120: this.bits = (unsigned char)1;
! 121: this.val = (unsigned short)0;
! 122: *(*table)++ = this; /* make a table to force an error */
! 123: *(*table)++ = this;
! 124: *bits = 1;
! 125: return 0; /* no symbols, but wait for decoding to report error */
! 126: }
! 127: for (min = 1; min <= MAXBITS; min++)
! 128: if (count[min] != 0) break;
! 129: if (root < min) root = min;
! 130:
! 131: /* check for an over-subscribed or incomplete set of lengths */
! 132: left = 1;
! 133: for (len = 1; len <= MAXBITS; len++) {
! 134: left <<= 1;
! 135: left -= count[len];
! 136: if (left < 0) return -1; /* over-subscribed */
! 137: }
! 138: if (left > 0 && (type == CODES || max != 1))
! 139: return -1; /* incomplete set */
! 140:
! 141: /* generate offsets into symbol table for each length for sorting */
! 142: offs[1] = 0;
! 143: for (len = 1; len < MAXBITS; len++)
! 144: offs[len + 1] = offs[len] + count[len];
! 145:
! 146: /* sort symbols by length, by symbol order within each length */
! 147: for (sym = 0; sym < codes; sym++)
! 148: if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
! 149:
! 150: /*
! 151: Create and fill in decoding tables. In this loop, the table being
! 152: filled is at next and has curr index bits. The code being used is huff
! 153: with length len. That code is converted to an index by dropping drop
! 154: bits off of the bottom. For codes where len is less than drop + curr,
! 155: those top drop + curr - len bits are incremented through all values to
! 156: fill the table with replicated entries.
! 157:
! 158: root is the number of index bits for the root table. When len exceeds
! 159: root, sub-tables are created pointed to by the root entry with an index
! 160: of the low root bits of huff. This is saved in low to check for when a
! 161: new sub-table should be started. drop is zero when the root table is
! 162: being filled, and drop is root when sub-tables are being filled.
! 163:
! 164: When a new sub-table is needed, it is necessary to look ahead in the
! 165: code lengths to determine what size sub-table is needed. The length
! 166: counts are used for this, and so count[] is decremented as codes are
! 167: entered in the tables.
! 168:
! 169: used keeps track of how many table entries have been allocated from the
! 170: provided *table space. It is checked when a LENS table is being made
! 171: against the space in *table, ENOUGH, minus the maximum space needed by
! 172: the worst case distance code, MAXD. This should never happen, but the
! 173: sufficiency of ENOUGH has not been proven exhaustively, hence the check.
! 174: This assumes that when type == LENS, bits == 9.
! 175:
! 176: sym increments through all symbols, and the loop terminates when
! 177: all codes of length max, i.e. all codes, have been processed. This
! 178: routine permits incomplete codes, so another loop after this one fills
! 179: in the rest of the decoding tables with invalid code markers.
! 180: */
! 181:
! 182: /* set up for code type */
! 183: switch (type) {
! 184: case CODES:
! 185: base = extra = work; /* dummy value--not used */
! 186: end = 19;
! 187: break;
! 188: case LENS:
! 189: base = lbase;
! 190: base -= 257;
! 191: extra = lext;
! 192: extra -= 257;
! 193: end = 256;
! 194: break;
! 195: default: /* DISTS */
! 196: base = dbase;
! 197: extra = dext;
! 198: end = -1;
! 199: }
! 200:
! 201: /* initialize state for loop */
! 202: huff = 0; /* starting code */
! 203: sym = 0; /* starting code symbol */
! 204: len = min; /* starting code length */
! 205: next = *table; /* current table to fill in */
! 206: curr = root; /* current table index bits */
! 207: drop = 0; /* current bits to drop from code for index */
! 208: low = (unsigned)(-1); /* trigger new sub-table when len > root */
! 209: used = 1U << root; /* use root table entries */
! 210: mask = used - 1; /* mask for comparing low */
! 211:
! 212: /* check available table space */
! 213: if (type == LENS && used >= ENOUGH - MAXD)
! 214: return 1;
! 215:
! 216: /* process all codes and make table entries */
! 217: for (;;) {
! 218: /* create table entry */
! 219: this.bits = (unsigned char)(len - drop);
! 220: if ((int)(work[sym]) < end) {
! 221: this.op = (unsigned char)0;
! 222: this.val = work[sym];
! 223: }
! 224: else if ((int)(work[sym]) > end) {
! 225: this.op = (unsigned char)(extra[work[sym]]);
! 226: this.val = base[work[sym]];
! 227: }
! 228: else {
! 229: this.op = (unsigned char)(32 + 64); /* end of block */
! 230: this.val = 0;
! 231: }
! 232:
! 233: /* replicate for those indices with low len bits equal to huff */
! 234: incr = 1U << (len - drop);
! 235: fill = 1U << curr;
! 236: min = fill; /* save offset to next table */
! 237: do {
! 238: fill -= incr;
! 239: next[(huff >> drop) + fill] = this;
! 240: } while (fill != 0);
! 241:
! 242: /* backwards increment the len-bit code huff */
! 243: incr = 1U << (len - 1);
! 244: while (huff & incr)
! 245: incr >>= 1;
! 246: if (incr != 0) {
! 247: huff &= incr - 1;
! 248: huff += incr;
! 249: }
! 250: else
! 251: huff = 0;
! 252:
! 253: /* go to next symbol, update count, len */
! 254: sym++;
! 255: if (--(count[len]) == 0) {
! 256: if (len == max) break;
! 257: len = lens[work[sym]];
! 258: }
! 259:
! 260: /* create new sub-table if needed */
! 261: if (len > root && (huff & mask) != low) {
! 262: /* if first time, transition to sub-tables */
! 263: if (drop == 0)
! 264: drop = root;
! 265:
! 266: /* increment past last table */
! 267: next += min; /* here min is 1 << curr */
! 268:
! 269: /* determine length of next table */
! 270: curr = len - drop;
! 271: left = (int)(1 << curr);
! 272: while (curr + drop < max) {
! 273: left -= count[curr + drop];
! 274: if (left <= 0) break;
! 275: curr++;
! 276: left <<= 1;
! 277: }
! 278:
! 279: /* check for enough space */
! 280: used += 1U << curr;
! 281: if (type == LENS && used >= ENOUGH - MAXD)
! 282: return 1;
! 283:
! 284: /* point entry in root table to sub-table */
! 285: low = huff & mask;
! 286: (*table)[low].op = (unsigned char)curr;
! 287: (*table)[low].bits = (unsigned char)root;
! 288: (*table)[low].val = (unsigned short)(next - *table);
! 289: }
! 290: }
! 291:
! 292: /*
! 293: Fill in rest of table for incomplete codes. This loop is similar to the
! 294: loop above in incrementing huff for table indices. It is assumed that
! 295: len is equal to curr + drop, so there is no loop needed to increment
! 296: through high index bits. When the current sub-table is filled, the loop
! 297: drops back to the root table to fill in any remaining entries there.
! 298: */
! 299: this.op = (unsigned char)64; /* invalid code marker */
! 300: this.bits = (unsigned char)(len - drop);
! 301: this.val = (unsigned short)0;
! 302: while (huff != 0) {
! 303: /* when done with sub-table, drop back to root table */
! 304: if (drop != 0 && (huff & mask) != low) {
! 305: drop = 0;
! 306: len = root;
! 307: next = *table;
! 308: this.bits = (unsigned char)len;
! 309: }
! 310:
! 311: /* put invalid code marker in table */
! 312: next[huff >> drop] = this;
! 313:
! 314: /* backwards increment the len-bit code huff */
! 315: incr = 1U << (len - 1);
! 316: while (huff & incr)
! 317: incr >>= 1;
! 318: if (incr != 0) {
! 319: huff &= incr - 1;
! 320: huff += incr;
! 321: }
! 322: else
! 323: huff = 0;
! 324: }
! 325:
! 326: /* set return parameters */
! 327: *table += used;
! 328: *bits = root;
! 329: return 0;
! 330: }
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