source: rtems/cpukit/zlib/inftrees.c @ 94a2ecc

4.11
Last change on this file since 94a2ecc was e215a4e1, checked in by Ralf Corsepius <ralf.corsepius@…>, on Mar 18, 2011 at 10:11:28 AM

Import from zlib-1.2.4

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1/* inftrees.c -- generate Huffman trees for efficient decoding
2 * Copyright (C) 1995-2010 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 1.2.4 Copyright 1995-2010 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 here;                  /* 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, 64, 195};
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        here.op = (unsigned char)64;    /* invalid code marker */
119        here.bits = (unsigned char)1;
120        here.val = (unsigned short)0;
121        *(*table)++ = here;             /* make a table to force an error */
122        *(*table)++ = here;
123        *bits = 1;
124        return 0;     /* no symbols, but wait for decoding to report error */
125    }
126    for (min = 1; min < max; 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 for LENS and DIST tables against
170       the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in
171       the initial root table size constants.  See the comments in inftrees.h
172       for more information.
173
174       sym increments through all symbols, and the loop terminates when
175       all codes of length max, i.e. all codes, have been processed.  This
176       routine permits incomplete codes, so another loop after this one fills
177       in the rest of the decoding tables with invalid code markers.
178     */
179
180    /* set up for code type */
181    switch (type) {
182    case CODES:
183        base = extra = work;    /* dummy value--not used */
184        end = 19;
185        break;
186    case LENS:
187        base = lbase;
188        base -= 257;
189        extra = lext;
190        extra -= 257;
191        end = 256;
192        break;
193    default:            /* DISTS */
194        base = dbase;
195        extra = dext;
196        end = -1;
197    }
198
199    /* initialize state for loop */
200    huff = 0;                   /* starting code */
201    sym = 0;                    /* starting code symbol */
202    len = min;                  /* starting code length */
203    next = *table;              /* current table to fill in */
204    curr = root;                /* current table index bits */
205    drop = 0;                   /* current bits to drop from code for index */
206    low = (unsigned)(-1);       /* trigger new sub-table when len > root */
207    used = 1U << root;          /* use root table entries */
208    mask = used - 1;            /* mask for comparing low */
209
210    /* check available table space */
211    if ((type == LENS && used >= ENOUGH_LENS) ||
212        (type == DISTS && used >= ENOUGH_DISTS))
213        return 1;
214
215    /* process all codes and make table entries */
216    for (;;) {
217        /* create table entry */
218        here.bits = (unsigned char)(len - drop);
219        if ((int)(work[sym]) < end) {
220            here.op = (unsigned char)0;
221            here.val = work[sym];
222        }
223        else if ((int)(work[sym]) > end) {
224            here.op = (unsigned char)(extra[work[sym]]);
225            here.val = base[work[sym]];
226        }
227        else {
228            here.op = (unsigned char)(32 + 64);         /* end of block */
229            here.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] = here;
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_LENS) ||
281                (type == DISTS && used >= ENOUGH_DISTS))
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    here.op = (unsigned char)64;                /* invalid code marker */
300    here.bits = (unsigned char)(len - drop);
301    here.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            here.bits = (unsigned char)len;
309        }
310
311        /* put invalid code marker in table */
312        next[huff >> drop] = here;
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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