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lightning-sunbird  0.9+nobinonly
inftrees.c
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00001 /* inftrees.c -- generate Huffman trees for efficient decoding
00002  * Copyright (C) 1995-2005 Mark Adler
00003  * For conditions of distribution and use, see copyright notice in zlib.h
00004  */
00005 
00006 #include "zutil.h"
00007 #include "inftrees.h"
00008 
00009 #define MAXBITS 15
00010 
00011 const char inflate_copyright[] =
00012    " inflate 1.2.3 Copyright 1995-2005 Mark Adler ";
00013 /*
00014   If you use the zlib library in a product, an acknowledgment is welcome
00015   in the documentation of your product. If for some reason you cannot
00016   include such an acknowledgment, I would appreciate that you keep this
00017   copyright string in the executable of your product.
00018  */
00019 
00020 /*
00021    Build a set of tables to decode the provided canonical Huffman code.
00022    The code lengths are lens[0..codes-1].  The result starts at *table,
00023    whose indices are 0..2^bits-1.  work is a writable array of at least
00024    lens shorts, which is used as a work area.  type is the type of code
00025    to be generated, CODES, LENS, or DISTS.  On return, zero is success,
00026    -1 is an invalid code, and +1 means that ENOUGH isn't enough.  table
00027    on return points to the next available entry's address.  bits is the
00028    requested root table index bits, and on return it is the actual root
00029    table index bits.  It will differ if the request is greater than the
00030    longest code or if it is less than the shortest code.
00031  */
00032 int inflate_table(type, lens, codes, table, bits, work)
00033 codetype type;
00034 unsigned short FAR *lens;
00035 unsigned codes;
00036 code FAR * FAR *table;
00037 unsigned FAR *bits;
00038 unsigned short FAR *work;
00039 {
00040     unsigned len;               /* a code's length in bits */
00041     unsigned sym;               /* index of code symbols */
00042     unsigned min, max;          /* minimum and maximum code lengths */
00043     unsigned root;              /* number of index bits for root table */
00044     unsigned curr;              /* number of index bits for current table */
00045     unsigned drop;              /* code bits to drop for sub-table */
00046     int left;                   /* number of prefix codes available */
00047     unsigned used;              /* code entries in table used */
00048     unsigned huff;              /* Huffman code */
00049     unsigned incr;              /* for incrementing code, index */
00050     unsigned fill;              /* index for replicating entries */
00051     unsigned low;               /* low bits for current root entry */
00052     unsigned mask;              /* mask for low root bits */
00053     code this;                  /* table entry for duplication */
00054     code FAR *next;             /* next available space in table */
00055     const unsigned short FAR *base;     /* base value table to use */
00056     const unsigned short FAR *extra;    /* extra bits table to use */
00057     int end;                    /* use base and extra for symbol > end */
00058     unsigned short count[MAXBITS+1];    /* number of codes of each length */
00059     unsigned short offs[MAXBITS+1];     /* offsets in table for each length */
00060     static const unsigned short lbase[31] = { /* Length codes 257..285 base */
00061         3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
00062         35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
00063     static const unsigned short lext[31] = { /* Length codes 257..285 extra */
00064         16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
00065         19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 201, 196};
00066     static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
00067         1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
00068         257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
00069         8193, 12289, 16385, 24577, 0, 0};
00070     static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
00071         16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
00072         23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
00073         28, 28, 29, 29, 64, 64};
00074 
00075     /*
00076        Process a set of code lengths to create a canonical Huffman code.  The
00077        code lengths are lens[0..codes-1].  Each length corresponds to the
00078        symbols 0..codes-1.  The Huffman code is generated by first sorting the
00079        symbols by length from short to long, and retaining the symbol order
00080        for codes with equal lengths.  Then the code starts with all zero bits
00081        for the first code of the shortest length, and the codes are integer
00082        increments for the same length, and zeros are appended as the length
00083        increases.  For the deflate format, these bits are stored backwards
00084        from their more natural integer increment ordering, and so when the
00085        decoding tables are built in the large loop below, the integer codes
00086        are incremented backwards.
00087 
00088        This routine assumes, but does not check, that all of the entries in
00089        lens[] are in the range 0..MAXBITS.  The caller must assure this.
00090        1..MAXBITS is interpreted as that code length.  zero means that that
00091        symbol does not occur in this code.
00092 
00093        The codes are sorted by computing a count of codes for each length,
00094        creating from that a table of starting indices for each length in the
00095        sorted table, and then entering the symbols in order in the sorted
00096        table.  The sorted table is work[], with that space being provided by
00097        the caller.
00098 
00099        The length counts are used for other purposes as well, i.e. finding
00100        the minimum and maximum length codes, determining if there are any
00101        codes at all, checking for a valid set of lengths, and looking ahead
00102        at length counts to determine sub-table sizes when building the
00103        decoding tables.
00104      */
00105 
00106     /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
00107     for (len = 0; len <= MAXBITS; len++)
00108         count[len] = 0;
00109     for (sym = 0; sym < codes; sym++)
00110         count[lens[sym]]++;
00111 
00112     /* bound code lengths, force root to be within code lengths */
00113     root = *bits;
00114     for (max = MAXBITS; max >= 1; max--)
00115         if (count[max] != 0) break;
00116     if (root > max) root = max;
00117     if (max == 0) {                     /* no symbols to code at all */
00118         this.op = (unsigned char)64;    /* invalid code marker */
00119         this.bits = (unsigned char)1;
00120         this.val = (unsigned short)0;
00121         *(*table)++ = this;             /* make a table to force an error */
00122         *(*table)++ = this;
00123         *bits = 1;
00124         return 0;     /* no symbols, but wait for decoding to report error */
00125     }
00126     for (min = 1; min <= MAXBITS; min++)
00127         if (count[min] != 0) break;
00128     if (root < min) root = min;
00129 
00130     /* check for an over-subscribed or incomplete set of lengths */
00131     left = 1;
00132     for (len = 1; len <= MAXBITS; len++) {
00133         left <<= 1;
00134         left -= count[len];
00135         if (left < 0) return -1;        /* over-subscribed */
00136     }
00137     if (left > 0 && (type == CODES || max != 1))
00138         return -1;                      /* incomplete set */
00139 
00140     /* generate offsets into symbol table for each length for sorting */
00141     offs[1] = 0;
00142     for (len = 1; len < MAXBITS; len++)
00143         offs[len + 1] = offs[len] + count[len];
00144 
00145     /* sort symbols by length, by symbol order within each length */
00146     for (sym = 0; sym < codes; sym++)
00147         if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
00148 
00149     /*
00150        Create and fill in decoding tables.  In this loop, the table being
00151        filled is at next and has curr index bits.  The code being used is huff
00152        with length len.  That code is converted to an index by dropping drop
00153        bits off of the bottom.  For codes where len is less than drop + curr,
00154        those top drop + curr - len bits are incremented through all values to
00155        fill the table with replicated entries.
00156 
00157        root is the number of index bits for the root table.  When len exceeds
00158        root, sub-tables are created pointed to by the root entry with an index
00159        of the low root bits of huff.  This is saved in low to check for when a
00160        new sub-table should be started.  drop is zero when the root table is
00161        being filled, and drop is root when sub-tables are being filled.
00162 
00163        When a new sub-table is needed, it is necessary to look ahead in the
00164        code lengths to determine what size sub-table is needed.  The length
00165        counts are used for this, and so count[] is decremented as codes are
00166        entered in the tables.
00167 
00168        used keeps track of how many table entries have been allocated from the
00169        provided *table space.  It is checked when a LENS table is being made
00170        against the space in *table, ENOUGH, minus the maximum space needed by
00171        the worst case distance code, MAXD.  This should never happen, but the
00172        sufficiency of ENOUGH has not been proven exhaustively, hence the check.
00173        This assumes that when type == LENS, bits == 9.
00174 
00175        sym increments through all symbols, and the loop terminates when
00176        all codes of length max, i.e. all codes, have been processed.  This
00177        routine permits incomplete codes, so another loop after this one fills
00178        in the rest of the decoding tables with invalid code markers.
00179      */
00180 
00181     /* set up for code type */
00182     switch (type) {
00183     case CODES:
00184         base = extra = work;    /* dummy value--not used */
00185         end = 19;
00186         break;
00187     case LENS:
00188         base = lbase;
00189         base -= 257;
00190         extra = lext;
00191         extra -= 257;
00192         end = 256;
00193         break;
00194     default:            /* DISTS */
00195         base = dbase;
00196         extra = dext;
00197         end = -1;
00198     }
00199 
00200     /* initialize state for loop */
00201     huff = 0;                   /* starting code */
00202     sym = 0;                    /* starting code symbol */
00203     len = min;                  /* starting code length */
00204     next = *table;              /* current table to fill in */
00205     curr = root;                /* current table index bits */
00206     drop = 0;                   /* current bits to drop from code for index */
00207     low = (unsigned)(-1);       /* trigger new sub-table when len > root */
00208     used = 1U << root;          /* use root table entries */
00209     mask = used - 1;            /* mask for comparing low */
00210 
00211     /* check available table space */
00212     if (type == LENS && used >= ENOUGH - MAXD)
00213         return 1;
00214 
00215     /* process all codes and make table entries */
00216     for (;;) {
00217         /* create table entry */
00218         this.bits = (unsigned char)(len - drop);
00219         if ((int)(work[sym]) < end) {
00220             this.op = (unsigned char)0;
00221             this.val = work[sym];
00222         }
00223         else if ((int)(work[sym]) > end) {
00224             this.op = (unsigned char)(extra[work[sym]]);
00225             this.val = base[work[sym]];
00226         }
00227         else {
00228             this.op = (unsigned char)(32 + 64);         /* end of block */
00229             this.val = 0;
00230         }
00231 
00232         /* replicate for those indices with low len bits equal to huff */
00233         incr = 1U << (len - drop);
00234         fill = 1U << curr;
00235         min = fill;                 /* save offset to next table */
00236         do {
00237             fill -= incr;
00238             next[(huff >> drop) + fill] = this;
00239         } while (fill != 0);
00240 
00241         /* backwards increment the len-bit code huff */
00242         incr = 1U << (len - 1);
00243         while (huff & incr)
00244             incr >>= 1;
00245         if (incr != 0) {
00246             huff &= incr - 1;
00247             huff += incr;
00248         }
00249         else
00250             huff = 0;
00251 
00252         /* go to next symbol, update count, len */
00253         sym++;
00254         if (--(count[len]) == 0) {
00255             if (len == max) break;
00256             len = lens[work[sym]];
00257         }
00258 
00259         /* create new sub-table if needed */
00260         if (len > root && (huff & mask) != low) {
00261             /* if first time, transition to sub-tables */
00262             if (drop == 0)
00263                 drop = root;
00264 
00265             /* increment past last table */
00266             next += min;            /* here min is 1 << curr */
00267 
00268             /* determine length of next table */
00269             curr = len - drop;
00270             left = (int)(1 << curr);
00271             while (curr + drop < max) {
00272                 left -= count[curr + drop];
00273                 if (left <= 0) break;
00274                 curr++;
00275                 left <<= 1;
00276             }
00277 
00278             /* check for enough space */
00279             used += 1U << curr;
00280             if (type == LENS && used >= ENOUGH - MAXD)
00281                 return 1;
00282 
00283             /* point entry in root table to sub-table */
00284             low = huff & mask;
00285             (*table)[low].op = (unsigned char)curr;
00286             (*table)[low].bits = (unsigned char)root;
00287             (*table)[low].val = (unsigned short)(next - *table);
00288         }
00289     }
00290 
00291     /*
00292        Fill in rest of table for incomplete codes.  This loop is similar to the
00293        loop above in incrementing huff for table indices.  It is assumed that
00294        len is equal to curr + drop, so there is no loop needed to increment
00295        through high index bits.  When the current sub-table is filled, the loop
00296        drops back to the root table to fill in any remaining entries there.
00297      */
00298     this.op = (unsigned char)64;                /* invalid code marker */
00299     this.bits = (unsigned char)(len - drop);
00300     this.val = (unsigned short)0;
00301     while (huff != 0) {
00302         /* when done with sub-table, drop back to root table */
00303         if (drop != 0 && (huff & mask) != low) {
00304             drop = 0;
00305             len = root;
00306             next = *table;
00307             this.bits = (unsigned char)len;
00308         }
00309 
00310         /* put invalid code marker in table */
00311         next[huff >> drop] = this;
00312 
00313         /* backwards increment the len-bit code huff */
00314         incr = 1U << (len - 1);
00315         while (huff & incr)
00316             incr >>= 1;
00317         if (incr != 0) {
00318             huff &= incr - 1;
00319             huff += incr;
00320         }
00321         else
00322             huff = 0;
00323     }
00324 
00325     /* set return parameters */
00326     *table += used;
00327     *bits = root;
00328     return 0;
00329 }