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