1			/* inftrees.c -- generate Huffman trees for efficient decoding
     2			 * Copyright (C) 1995-2004 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 1.2.2 Copyright 1995-2004 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	          60    {
    40	          60        unsigned len;               /* a code's length in bits */
    41	          60        unsigned sym;               /* index of code symbols */
    42	          60        unsigned min, max;          /* minimum and maximum code lengths */
    43	          60        unsigned root;              /* number of index bits for root table */
    44	          60        unsigned curr;              /* number of index bits for current table */
    45	          60        unsigned drop;              /* code bits to drop for sub-table */
    46	          60        int left;                   /* number of prefix codes available */
    47	          60        unsigned used;              /* code entries in table used */
    48	          60        unsigned huff;              /* Huffman code */
    49	          60        unsigned incr;              /* for incrementing code, index */
    50	          60        unsigned fill;              /* index for replicating entries */
    51	          60        unsigned low;               /* low bits for current root entry */
    52	          60        unsigned mask;              /* mask for low root bits */
    53	          60        code this;                  /* table entry for duplication */
    54	          60        code FAR *next;             /* next available space in table */
    55	          60        const unsigned short FAR *base;     /* base value table to use */
    56	          60        const unsigned short FAR *extra;    /* extra bits table to use */
    57	          60        int end;                    /* use base and extra for symbol > end */
    58	          60        unsigned short count[MAXBITS+1];    /* number of codes of each length */
    59	          60        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	          60            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	          60            19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 199, 198};
    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	          60            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	          60            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	        1020        for (len = 0; len <= MAXBITS; len++)
   108	         960            count[len] = 0;
   109	        6402        for (sym = 0; sym < codes; sym++)
   110	        6342            count[lens[sym]]++;
   111			
   112			    /* bound code lengths, force root to be within code lengths */
   113	          60        root = *bits;
   114	         611        for (max = MAXBITS; max >= 1; max--)
   115	         611            if (count[max] != 0) break;
   116	          60        if (root > max) root = max;
   117	          60        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	         138        for (min = 1; min <= MAXBITS; min++)
   127	         138            if (count[min] != 0) break;
   128	          60        if (root < min) root = min;
   129			
   130			    /* check for an over-subscribed or incomplete set of lengths */
   131	          60        left = 1;
   132	         960        for (len = 1; len <= MAXBITS; len++) {
   133	         900            left <<= 1;
   134	         900            left -= count[len];
   135	         900            if (left < 0) return -1;        /* over-subscribed */
   136			    }
   137	          60        if (left > 0 && (type == CODES || (codes - count[0] != 1)))
   138	      ######            return -1;                      /* incomplete set */
   139			
   140			    /* generate offsets into symbol table for each length for sorting */
   141	          60        offs[1] = 0;
   142	         900        for (len = 1; len < MAXBITS; len++)
   143	         840            offs[len + 1] = offs[len] + count[len];
   144			
   145			    /* sort symbols by length, by symbol order within each length */
   146	        6402        for (sym = 0; sym < codes; sym++)
   147	        6342            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	          60        switch (type) {
   183			    case CODES:
   184	          20            base = extra = work;    /* dummy value--not used */
   185	          20            end = 19;
   186	          20            break;
   187			    case LENS:
   188	          20            base = lbase;
   189	          20            base -= 257;
   190	          20            extra = lext;
   191	          20            extra -= 257;
   192	          20            end = 256;
   193	          20            break;
   194			    default:            /* DISTS */
   195	          20            base = dbase;
   196	          20            extra = dext;
   197	          20            end = -1;
   198			    }
   199			
   200			    /* initialize state for loop */
   201	          60        huff = 0;                   /* starting code */
   202	          60        sym = 0;                    /* starting code symbol */
   203	          60        len = min;                  /* starting code length */
   204	          60        next = *table;              /* current table to fill in */
   205	          60        curr = root;                /* current table index bits */
   206	          60        drop = 0;                   /* current bits to drop from code for index */
   207	          60        low = (unsigned)(-1);       /* trigger new sub-table when len > root */
   208	          60        used = 1U << root;          /* use root table entries */
   209	          60        mask = used - 1;            /* mask for comparing low */
   210			
   211			    /* check available table space */
   212	          60        if (type == LENS && used >= ENOUGH - MAXD)
   213	      ######            return 1;
   214			
   215			    /* process all codes and make table entries */
   216	        1668        for (;;) {
   217			        /* create table entry */
   218	        1583            this.bits = (unsigned char)(len - drop);
   219	        1583            if ((int)(work[sym]) < end) {
   220	        1037                this.op = (unsigned char)0;
   221	        1037                this.val = work[sym];
   222			        }
   223	         546            else if ((int)(work[sym]) > end) {
   224	         526                this.op = (unsigned char)(extra[work[sym]]);
   225	         526                this.val = base[work[sym]];
   226			        }
   227			        else {
   228	          20                this.op = (unsigned char)(32 + 64);         /* end of block */
   229	          20                this.val = 0;
   230			        }
   231			
   232			        /* replicate for those indices with low len bits equal to huff */
   233	        1583            incr = 1U << (len - drop);
   234	        1583            fill = 1U << curr;
   235	        5973            do {
   236	        5973                fill -= incr;
   237	        5973                next[(huff >> drop) + fill] = this;
   238	        5973            } while (fill != 0);
   239			
   240			        /* backwards increment the len-bit code huff */
   241	        1583            incr = 1U << (len - 1);
   242	        3106            while (huff & incr)
   243	        1523                incr >>= 1;
   244	        1583            if (incr != 0) {
   245	        1523                huff &= incr - 1;
   246	        1523                huff += incr;
   247			        }
   248			        else
   249	          60                huff = 0;
   250			
   251			        /* go to next symbol, update count, len */
   252	        1583            sym++;
   253	        1583            if (--(count[len]) == 0) {
   254	         261                if (len == max) break;
   255	         201                len = lens[work[sym]];
   256			        }
   257			
   258			        /* create new sub-table if needed */
   259	        1523            if (len > root && (huff & mask) != low) {
   260			            /* if first time, transition to sub-tables */
   261	          85                if (drop == 0)
   262	          13                    drop = root;
   263			
   264			            /* increment past last table */
   265	          85                next += 1U << curr;
   266			
   267			            /* determine length of next table */
   268	          85                curr = len - drop;
   269	          85                left = (int)(1 << curr);
   270	         115                while (curr + drop < max) {
   271	         102                    left -= count[curr + drop];
   272	         102                    if (left <= 0) break;
   273	          30                    curr++;
   274	          30                    left <<= 1;
   275			            }
   276			
   277			            /* check for enough space */
   278	          85                used += 1U << curr;
   279	          85                if (type == LENS && used >= ENOUGH - MAXD)
   280	      ######                    return 1;
   281			
   282			            /* point entry in root table to sub-table */
   283	          85                low = huff & mask;
   284	          85                (*table)[low].op = (unsigned char)curr;
   285	          85                (*table)[low].bits = (unsigned char)root;
   286	          85                (*table)[low].val = (unsigned short)(next - *table);
   287			        }
   288			    }
   289			
   290			    /*
   291			       Fill in rest of table for incomplete codes.  This loop is similar to the
   292			       loop above in incrementing huff for table indices.  It is assumed that
   293			       len is equal to curr + drop, so there is no loop needed to increment
   294			       through high index bits.  When the current sub-table is filled, the loop
   295			       drops back to the root table to fill in any remaining entries there.
   296			     */
   297	          60        this.op = (unsigned char)64;                /* invalid code marker */
   298	          60        this.bits = (unsigned char)(len - drop);
   299	          60        this.val = (unsigned short)0;
   300	          60        while (huff != 0) {
   301			        /* when done with sub-table, drop back to root table */
   302	      ######            if (drop != 0 && (huff & mask) != low) {
   303	      ######                drop = 0;
   304	      ######                len = root;
   305	      ######                next = *table;
   306	      ######                this.bits = (unsigned char)len;
   307			        }
   308			
   309			        /* put invalid code marker in table */
   310	      ######            next[huff >> drop] = this;
   311			
   312			        /* backwards increment the len-bit code huff */
   313	      ######            incr = 1U << (len - 1);
   314	      ######            while (huff & incr)
   315	      ######                incr >>= 1;
   316	      ######            if (incr != 0) {
   317	      ######                huff &= incr - 1;
   318	      ######                huff += incr;
   319			        }
   320			        else
   321	      ######                huff = 0;
   322			    }
   323			
   324			    /* set return parameters */
   325	          60        *table += used;
   326	          60        *bits = root;
   327	          60        return 0;
   328			}