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#pragma ident	"%Z%%M%	%I%	%E% SMI"
7
8#include "zutil.h"
9#include "inftrees.h"
10
11#define MAXBITS 15
12
13static const char inflate_copyright[] =
14   " inflate 1.2.3 Copyright 1995-2005 Mark Adler ";
15/*
16  If you use the zlib library in a product, an acknowledgment is welcome
17  in the documentation of your product. If for some reason you cannot
18  include such an acknowledgment, I would appreciate that you keep this
19  copyright string in the executable of your product.
20 */
21
22/*
23   Build a set of tables to decode the provided canonical Huffman code.
24   The code lengths are lens[0..codes-1].  The result starts at *table,
25   whose indices are 0..2^bits-1.  work is a writable array of at least
26   lens shorts, which is used as a work area.  type is the type of code
27   to be generated, CODES, LENS, or DISTS.  On return, zero is success,
28   -1 is an invalid code, and +1 means that ENOUGH isn't enough.  table
29   on return points to the next available entry's address.  bits is the
30   requested root table index bits, and on return it is the actual root
31   table index bits.  It will differ if the request is greater than the
32   longest code or if it is less than the shortest code.
33 */
34int inflate_table(type, lens, codes, table, bits, work)
35codetype type;
36unsigned short FAR *lens;
37unsigned codes;
38code FAR * FAR *table;
39unsigned FAR *bits;
40unsigned short FAR *work;
41{
42    unsigned len;               /* a code's length in bits */
43    unsigned sym;               /* index of code symbols */
44    unsigned min, max;          /* minimum and maximum code lengths */
45    unsigned root;              /* number of index bits for root table */
46    unsigned curr;              /* number of index bits for current table */
47    unsigned drop;              /* code bits to drop for sub-table */
48    int left;                   /* number of prefix codes available */
49    unsigned used;              /* code entries in table used */
50    unsigned huff;              /* Huffman code */
51    unsigned incr;              /* for incrementing code, index */
52    unsigned fill;              /* index for replicating entries */
53    unsigned low;               /* low bits for current root entry */
54    unsigned mask;              /* mask for low root bits */
55    code this;                  /* table entry for duplication */
56    code FAR *next;             /* next available space in table */
57    const unsigned short FAR *base;     /* base value table to use */
58    const unsigned short FAR *extra;    /* extra bits table to use */
59    int end;                    /* use base and extra for symbol > end */
60    unsigned short count[MAXBITS+1];    /* number of codes of each length */
61    unsigned short offs[MAXBITS+1];     /* offsets in table for each length */
62    static const unsigned short lbase[31] = { /* Length codes 257..285 base */
63        3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
64        35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
65    static const unsigned short lext[31] = { /* Length codes 257..285 extra */
66        16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
67        19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 201, 196};
68    static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
69        1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
70        257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
71        8193, 12289, 16385, 24577, 0, 0};
72    static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
73        16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
74        23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
75        28, 28, 29, 29, 64, 64};
76
77    /*
78       Process a set of code lengths to create a canonical Huffman code.  The
79       code lengths are lens[0..codes-1].  Each length corresponds to the
80       symbols 0..codes-1.  The Huffman code is generated by first sorting the
81       symbols by length from short to long, and retaining the symbol order
82       for codes with equal lengths.  Then the code starts with all zero bits
83       for the first code of the shortest length, and the codes are integer
84       increments for the same length, and zeros are appended as the length
85       increases.  For the deflate format, these bits are stored backwards
86       from their more natural integer increment ordering, and so when the
87       decoding tables are built in the large loop below, the integer codes
88       are incremented backwards.
89
90       This routine assumes, but does not check, that all of the entries in
91       lens[] are in the range 0..MAXBITS.  The caller must assure this.
92       1..MAXBITS is interpreted as that code length.  zero means that that
93       symbol does not occur in this code.
94
95       The codes are sorted by computing a count of codes for each length,
96       creating from that a table of starting indices for each length in the
97       sorted table, and then entering the symbols in order in the sorted
98       table.  The sorted table is work[], with that space being provided by
99       the caller.
100
101       The length counts are used for other purposes as well, i.e. finding
102       the minimum and maximum length codes, determining if there are any
103       codes at all, checking for a valid set of lengths, and looking ahead
104       at length counts to determine sub-table sizes when building the
105       decoding tables.
106     */
107
108    /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
109    for (len = 0; len <= MAXBITS; len++)
110        count[len] = 0;
111    for (sym = 0; sym < codes; sym++)
112        count[lens[sym]]++;
113
114    /* bound code lengths, force root to be within code lengths */
115    root = *bits;
116    for (max = MAXBITS; max >= 1; max--)
117        if (count[max] != 0) break;
118    if (root > max) root = max;
119    if (max == 0) {                     /* no symbols to code at all */
120        this.op = (unsigned char)64;    /* invalid code marker */
121        this.bits = (unsigned char)1;
122        this.val = (unsigned short)0;
123        *(*table)++ = this;             /* make a table to force an error */
124        *(*table)++ = this;
125        *bits = 1;
126        return 0;     /* no symbols, but wait for decoding to report error */
127    }
128    for (min = 1; min <= MAXBITS; min++)
129        if (count[min] != 0) break;
130    if (root < min) root = min;
131
132    /* check for an over-subscribed or incomplete set of lengths */
133    left = 1;
134    for (len = 1; len <= MAXBITS; len++) {
135        left <<= 1;
136        left -= count[len];
137        if (left < 0) return -1;        /* over-subscribed */
138    }
139    if (left > 0 && (type == CODES || max != 1))
140        return -1;                      /* incomplete set */
141
142    /* generate offsets into symbol table for each length for sorting */
143    offs[1] = 0;
144    for (len = 1; len < MAXBITS; len++)
145        offs[len + 1] = offs[len] + count[len];
146
147    /* sort symbols by length, by symbol order within each length */
148    for (sym = 0; sym < codes; sym++)
149        if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
150
151    /*
152       Create and fill in decoding tables.  In this loop, the table being
153       filled is at next and has curr index bits.  The code being used is huff
154       with length len.  That code is converted to an index by dropping drop
155       bits off of the bottom.  For codes where len is less than drop + curr,
156       those top drop + curr - len bits are incremented through all values to
157       fill the table with replicated entries.
158
159       root is the number of index bits for the root table.  When len exceeds
160       root, sub-tables are created pointed to by the root entry with an index
161       of the low root bits of huff.  This is saved in low to check for when a
162       new sub-table should be started.  drop is zero when the root table is
163       being filled, and drop is root when sub-tables are being filled.
164
165       When a new sub-table is needed, it is necessary to look ahead in the
166       code lengths to determine what size sub-table is needed.  The length
167       counts are used for this, and so count[] is decremented as codes are
168       entered in the tables.
169
170       used keeps track of how many table entries have been allocated from the
171       provided *table space.  It is checked when a LENS table is being made
172       against the space in *table, ENOUGH, minus the maximum space needed by
173       the worst case distance code, MAXD.  This should never happen, but the
174       sufficiency of ENOUGH has not been proven exhaustively, hence the check.
175       This assumes that when type == LENS, bits == 9.
176
177       sym increments through all symbols, and the loop terminates when
178       all codes of length max, i.e. all codes, have been processed.  This
179       routine permits incomplete codes, so another loop after this one fills
180       in the rest of the decoding tables with invalid code markers.
181     */
182
183    /* set up for code type */
184    switch (type) {
185    case CODES:
186        base = extra = work;    /* dummy value--not used */
187        end = 19;
188        break;
189    case LENS:
190        base = lbase;
191        base -= 257;
192        extra = lext;
193        extra -= 257;
194        end = 256;
195        break;
196    default:            /* DISTS */
197        base = dbase;
198        extra = dext;
199        end = -1;
200    }
201
202    /* initialize state for loop */
203    huff = 0;                   /* starting code */
204    sym = 0;                    /* starting code symbol */
205    len = min;                  /* starting code length */
206    next = *table;              /* current table to fill in */
207    curr = root;                /* current table index bits */
208    drop = 0;                   /* current bits to drop from code for index */
209    low = (unsigned)(-1);       /* trigger new sub-table when len > root */
210    used = 1U << root;          /* use root table entries */
211    mask = used - 1;            /* mask for comparing low */
212
213    /* check available table space */
214    if (type == LENS && used >= ENOUGH - MAXD)
215        return 1;
216
217    /* process all codes and make table entries */
218    for (;;) {
219        /* create table entry */
220        this.bits = (unsigned char)(len - drop);
221        if ((int)(work[sym]) < end) {
222            this.op = (unsigned char)0;
223            this.val = work[sym];
224        }
225        else if ((int)(work[sym]) > end) {
226            this.op = (unsigned char)(extra[work[sym]]);
227            this.val = base[work[sym]];
228        }
229        else {
230            this.op = (unsigned char)(32 + 64);         /* end of block */
231            this.val = 0;
232        }
233
234        /* replicate for those indices with low len bits equal to huff */
235        incr = 1U << (len - drop);
236        fill = 1U << curr;
237        min = fill;                 /* save offset to next table */
238        do {
239            fill -= incr;
240            next[(huff >> drop) + fill] = this;
241        } while (fill != 0);
242
243        /* backwards increment the len-bit code huff */
244        incr = 1U << (len - 1);
245        while (huff & incr)
246            incr >>= 1;
247        if (incr != 0) {
248            huff &= incr - 1;
249            huff += incr;
250        }
251        else
252            huff = 0;
253
254        /* go to next symbol, update count, len */
255        sym++;
256        if (--(count[len]) == 0) {
257            if (len == max) break;
258            len = lens[work[sym]];
259        }
260
261        /* create new sub-table if needed */
262        if (len > root && (huff & mask) != low) {
263            /* if first time, transition to sub-tables */
264            if (drop == 0)
265                drop = root;
266
267            /* increment past last table */
268            next += min;            /* here min is 1 << curr */
269
270            /* determine length of next table */
271            curr = len - drop;
272            left = (int)(1 << curr);
273            while (curr + drop < max) {
274                left -= count[curr + drop];
275                if (left <= 0) break;
276                curr++;
277                left <<= 1;
278            }
279
280            /* check for enough space */
281            used += 1U << curr;
282            if (type == LENS && used >= ENOUGH - MAXD)
283                return 1;
284
285            /* point entry in root table to sub-table */
286            low = huff & mask;
287            (*table)[low].op = (unsigned char)curr;
288            (*table)[low].bits = (unsigned char)root;
289            (*table)[low].val = (unsigned short)(next - *table);
290        }
291    }
292
293    /*
294       Fill in rest of table for incomplete codes.  This loop is similar to the
295       loop above in incrementing huff for table indices.  It is assumed that
296       len is equal to curr + drop, so there is no loop needed to increment
297       through high index bits.  When the current sub-table is filled, the loop
298       drops back to the root table to fill in any remaining entries there.
299     */
300    this.op = (unsigned char)64;                /* invalid code marker */
301    this.bits = (unsigned char)(len - drop);
302    this.val = (unsigned short)0;
303    while (huff != 0) {
304        /* when done with sub-table, drop back to root table */
305        if (drop != 0 && (huff & mask) != low) {
306            drop = 0;
307            len = root;
308            next = *table;
309            this.bits = (unsigned char)len;
310        }
311
312        /* put invalid code marker in table */
313        next[huff >> drop] = this;
314
315        /* backwards increment the len-bit code huff */
316        incr = 1U << (len - 1);
317        while (huff & incr)
318            incr >>= 1;
319        if (incr != 0) {
320            huff &= incr - 1;
321            huff += incr;
322        }
323        else
324            huff = 0;
325    }
326
327    /* set return parameters */
328    *table += used;
329    *bits = root;
330    return 0;
331}
332