source: SVN/cambria/redboot/packages/services/compress/zlib/current/src/inftrees.c @ 1

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1/* inftrees.c -- generate Huffman trees for efficient decoding
2 * Copyright (C) 1995-2003 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
11const char inflate_copyright[] =
12   " inflate 1.2.1 Copyright 1995-2003 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 */
32int inflate_table(type, lens, codes, table, bits, work)
33codetype type;
34unsigned short FAR *lens;
35unsigned codes;
36code FAR * FAR *table;
37unsigned FAR *bits;
38unsigned 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, 76, 66};
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) return -1;            /* no codes! */
118    for (min = 1; min <= MAXBITS; min++)
119        if (count[min] != 0) break;
120    if (root < min) root = min;
121
122    /* check for an over-subscribed or incomplete set of lengths */
123    left = 1;
124    for (len = 1; len <= MAXBITS; len++) {
125        left <<= 1;
126        left -= count[len];
127        if (left < 0) return -1;        /* over-subscribed */
128    }
129    if (left > 0 && (type == CODES || (codes - count[0] != 1)))
130        return -1;                      /* incomplete set */
131
132    /* generate offsets into symbol table for each length for sorting */
133    offs[1] = 0;
134    for (len = 1; len < MAXBITS; len++)
135        offs[len + 1] = offs[len] + count[len];
136
137    /* sort symbols by length, by symbol order within each length */
138    for (sym = 0; sym < codes; sym++)
139        if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
140
141    /*
142       Create and fill in decoding tables.  In this loop, the table being
143       filled is at next and has curr index bits.  The code being used is huff
144       with length len.  That code is converted to an index by dropping drop
145       bits off of the bottom.  For codes where len is less than drop + curr,
146       those top drop + curr - len bits are incremented through all values to
147       fill the table with replicated entries.
148
149       root is the number of index bits for the root table.  When len exceeds
150       root, sub-tables are created pointed to by the root entry with an index
151       of the low root bits of huff.  This is saved in low to check for when a
152       new sub-table should be started.  drop is zero when the root table is
153       being filled, and drop is root when sub-tables are being filled.
154
155       When a new sub-table is needed, it is necessary to look ahead in the
156       code lengths to determine what size sub-table is needed.  The length
157       counts are used for this, and so count[] is decremented as codes are
158       entered in the tables.
159
160       used keeps track of how many table entries have been allocated from the
161       provided *table space.  It is checked when a LENS table is being made
162       against the space in *table, ENOUGH, minus the maximum space needed by
163       the worst case distance code, MAXD.  This should never happen, but the
164       sufficiency of ENOUGH has not been proven exhaustively, hence the check.
165       This assumes that when type == LENS, bits == 9.
166
167       sym increments through all symbols, and the loop terminates when
168       all codes of length max, i.e. all codes, have been processed.  This
169       routine permits incomplete codes, so another loop after this one fills
170       in the rest of the decoding tables with invalid code markers.
171     */
172
173    /* set up for code type */
174    switch (type) {
175    case CODES:
176        base = extra = work;    /* dummy value--not used */
177        end = 19;
178        break;
179    case LENS:
180        base = lbase;
181        base -= 257;
182        extra = lext;
183        extra -= 257;
184        end = 256;
185        break;
186    default:            /* DISTS */
187        base = dbase;
188        extra = dext;
189        end = -1;
190    }
191
192    /* initialize state for loop */
193    huff = 0;                   /* starting code */
194    sym = 0;                    /* starting code symbol */
195    len = min;                  /* starting code length */
196    next = *table;              /* current table to fill in */
197    curr = root;                /* current table index bits */
198    drop = 0;                   /* current bits to drop from code for index */
199    low = (unsigned)(-1);       /* trigger new sub-table when len > root */
200    used = 1U << root;          /* use root table entries */
201    mask = used - 1;            /* mask for comparing low */
202
203    /* check available table space */
204    if (type == LENS && used >= ENOUGH - MAXD)
205        return 1;
206
207    /* process all codes and make table entries */
208    for (;;) {
209        /* create table entry */
210        this.bits = (unsigned char)(len - drop);
211        if ((int)(work[sym]) < end) {
212            this.op = (unsigned char)0;
213            this.val = work[sym];
214        }
215        else if ((int)(work[sym]) > end) {
216            this.op = (unsigned char)(extra[work[sym]]);
217            this.val = base[work[sym]];
218        }
219        else {
220            this.op = (unsigned char)(32 + 64);         /* end of block */
221            this.val = 0;
222        }
223
224        /* replicate for those indices with low len bits equal to huff */
225        incr = 1U << (len - drop);
226        fill = 1U << curr;
227        do {
228            fill -= incr;
229            next[(huff >> drop) + fill] = this;
230        } while (fill != 0);
231
232        /* backwards increment the len-bit code huff */
233        incr = 1U << (len - 1);
234        while (huff & incr)
235            incr >>= 1;
236        if (incr != 0) {
237            huff &= incr - 1;
238            huff += incr;
239        }
240        else
241            huff = 0;
242
243        /* go to next symbol, update count, len */
244        sym++;
245        if (--(count[len]) == 0) {
246            if (len == max) break;
247            len = lens[work[sym]];
248        }
249
250        /* create new sub-table if needed */
251        if (len > root && (huff & mask) != low) {
252            /* if first time, transition to sub-tables */
253            if (drop == 0)
254                drop = root;
255
256            /* increment past last table */
257            next += 1U << curr;
258
259            /* determine length of next table */
260            curr = len - drop;
261            left = (int)(1 << curr);
262            while (curr + drop < max) {
263                left -= count[curr + drop];
264                if (left <= 0) break;
265                curr++;
266                left <<= 1;
267            }
268
269            /* check for enough space */
270            used += 1U << curr;
271            if (type == LENS && used >= ENOUGH - MAXD)
272                return 1;
273
274            /* point entry in root table to sub-table */
275            low = huff & mask;
276            (*table)[low].op = (unsigned char)curr;
277            (*table)[low].bits = (unsigned char)root;
278            (*table)[low].val = (unsigned short)(next - *table);
279        }
280    }
281
282    /*
283       Fill in rest of table for incomplete codes.  This loop is similar to the
284       loop above in incrementing huff for table indices.  It is assumed that
285       len is equal to curr + drop, so there is no loop needed to increment
286       through high index bits.  When the current sub-table is filled, the loop
287       drops back to the root table to fill in any remaining entries there.
288     */
289    this.op = (unsigned char)64;                /* invalid code marker */
290    this.bits = (unsigned char)(len - drop);
291    this.val = (unsigned short)0;
292    while (huff != 0) {
293        /* when done with sub-table, drop back to root table */
294        if (drop != 0 && (huff & mask) != low) {
295            drop = 0;
296            len = root;
297            next = *table;
298            curr = root;
299            this.bits = (unsigned char)len;
300        }
301
302        /* put invalid code marker in table */
303        next[huff >> drop] = this;
304
305        /* backwards increment the len-bit code huff */
306        incr = 1U << (len - 1);
307        while (huff & incr)
308            incr >>= 1;
309        if (incr != 0) {
310            huff &= incr - 1;
311            huff += incr;
312        }
313        else
314            huff = 0;
315    }
316
317    /* set return parameters */
318    *table += used;
319    *bits = root;
320    return 0;
321}
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