varnish-cache/lib/libvgz/inftrees.c
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/* inftrees.c -- generate Huffman trees for efficient decoding
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 * Copyright (C) 1995-2023 Mark Adler
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 * For conditions of distribution and use, see copyright notice in zlib.h
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 */
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#include "zutil.h"
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#include "inftrees.h"
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#define MAXBITS 15
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extern const char inflate_copyright[];
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const char inflate_copyright[] =
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   " inflate 1.3 Copyright 1995-2023 Mark Adler ";
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/*
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  If you use the zlib library in a product, an acknowledgment is welcome
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  in the documentation of your product. If for some reason you cannot
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  include such an acknowledgment, I would appreciate that you keep this
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  copyright string in the executable of your product.
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 */
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/*
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   Build a set of tables to decode the provided canonical Huffman code.
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   The code lengths are lens[0..codes-1].  The result starts at *table,
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   whose indices are 0..2^bits-1.  work is a writable array of at least
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   lens shorts, which is used as a work area.  type is the type of code
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   to be generated, CODES, LENS, or DISTS.  On return, zero is success,
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   -1 is an invalid code, and +1 means that ENOUGH isn't enough.  table
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   on return points to the next available entry's address.  bits is the
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   requested root table index bits, and on return it is the actual root
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   table index bits.  It will differ if the request is greater than the
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   longest code or if it is less than the shortest code.
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 */
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int ZLIB_INTERNAL inflate_table(codetype type, unsigned short FAR *lens,
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                                unsigned codes, code FAR * FAR *table,
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                                unsigned FAR *bits, unsigned short FAR *work) {
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    unsigned len;               /* a code's length in bits */
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    unsigned sym;               /* index of code symbols */
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    unsigned min, max;          /* minimum and maximum code lengths */
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    unsigned root;              /* number of index bits for root table */
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    unsigned curr;              /* number of index bits for current table */
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    unsigned drop;              /* code bits to drop for sub-table */
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    int left;                   /* number of prefix codes available */
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    unsigned used;              /* code entries in table used */
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    unsigned huff;              /* Huffman code */
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    unsigned incr;              /* for incrementing code, index */
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    unsigned fill;              /* index for replicating entries */
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    unsigned low;               /* low bits for current root entry */
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    unsigned mask;              /* mask for low root bits */
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    code here;                  /* table entry for duplication */
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    code FAR *next;             /* next available space in table */
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    const unsigned short FAR *base;     /* base value table to use */
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    const unsigned short FAR *extra;    /* extra bits table to use */
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    unsigned match;             /* use base and extra for symbol >= match */
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    unsigned short count[MAXBITS+1];    /* number of codes of each length */
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    unsigned short offs[MAXBITS+1];     /* offsets in table for each length */
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    static const unsigned short lbase[31] = { /* Length codes 257..285 base */
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        3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
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        35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
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    static const unsigned short lext[31] = { /* Length codes 257..285 extra */
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        16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
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        19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 198, 203};
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    static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
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        1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
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        257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
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        8193, 12289, 16385, 24577, 0, 0};
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    static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
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        16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
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        23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
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        28, 28, 29, 29, 64, 64};
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    /*
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       Process a set of code lengths to create a canonical Huffman code.  The
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       code lengths are lens[0..codes-1].  Each length corresponds to the
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       symbols 0..codes-1.  The Huffman code is generated by first sorting the
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       symbols by length from short to long, and retaining the symbol order
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       for codes with equal lengths.  Then the code starts with all zero bits
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       for the first code of the shortest length, and the codes are integer
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       increments for the same length, and zeros are appended as the length
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       increases.  For the deflate format, these bits are stored backwards
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       from their more natural integer increment ordering, and so when the
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       decoding tables are built in the large loop below, the integer codes
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       are incremented backwards.
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       This routine assumes, but does not check, that all of the entries in
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       lens[] are in the range 0..MAXBITS.  The caller must assure this.
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       1..MAXBITS is interpreted as that code length.  zero means that that
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       symbol does not occur in this code.
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       The codes are sorted by computing a count of codes for each length,
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       creating from that a table of starting indices for each length in the
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       sorted table, and then entering the symbols in order in the sorted
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       table.  The sorted table is work[], with that space being provided by
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       the caller.
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       The length counts are used for other purposes as well, i.e. finding
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       the minimum and maximum length codes, determining if there are any
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       codes at all, checking for a valid set of lengths, and looking ahead
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       at length counts to determine sub-table sizes when building the
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       decoding tables.
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     */
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    /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
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    for (len = 0; len <= MAXBITS; len++)
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        count[len] = 0;
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    for (sym = 0; sym < codes; sym++)
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        count[lens[sym]]++;
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    /* bound code lengths, force root to be within code lengths */
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    root = *bits;
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    for (max = MAXBITS; max >= 1; max--)
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        if (count[max] != 0) break;
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    if (root > max) root = max;
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    if (max == 0) {                     /* no symbols to code at all */
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        here.op = (unsigned char)64;    /* invalid code marker */
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        here.bits = (unsigned char)1;
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        here.val = (unsigned short)0;
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        *(*table)++ = here;             /* make a table to force an error */
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        *(*table)++ = here;
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        *bits = 1;
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        return 0;     /* no symbols, but wait for decoding to report error */
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    }
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    for (min = 1; min < max; min++)
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        if (count[min] != 0) break;
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    if (root < min) root = min;
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    /* check for an over-subscribed or incomplete set of lengths */
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    left = 1;
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    for (len = 1; len <= MAXBITS; len++) {
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        left <<= 1;
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        left -= count[len];
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        if (left < 0) return -1;        /* over-subscribed */
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    }
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    if (left > 0 && (type == CODES || max != 1))
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        return -1;                      /* incomplete set */
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    /* generate offsets into symbol table for each length for sorting */
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    offs[1] = 0;
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    for (len = 1; len < MAXBITS; len++)
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        offs[len + 1] = offs[len] + count[len];
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    /* sort symbols by length, by symbol order within each length */
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    for (sym = 0; sym < codes; sym++)
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        if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
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    /*
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       Create and fill in decoding tables.  In this loop, the table being
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       filled is at next and has curr index bits.  The code being used is huff
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       with length len.  That code is converted to an index by dropping drop
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       bits off of the bottom.  For codes where len is less than drop + curr,
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       those top drop + curr - len bits are incremented through all values to
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       fill the table with replicated entries.
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       root is the number of index bits for the root table.  When len exceeds
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       root, sub-tables are created pointed to by the root entry with an index
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       of the low root bits of huff.  This is saved in low to check for when a
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       new sub-table should be started.  drop is zero when the root table is
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       being filled, and drop is root when sub-tables are being filled.
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       When a new sub-table is needed, it is necessary to look ahead in the
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       code lengths to determine what size sub-table is needed.  The length
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       counts are used for this, and so count[] is decremented as codes are
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       entered in the tables.
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       used keeps track of how many table entries have been allocated from the
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       provided *table space.  It is checked for LENS and DIST tables against
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       the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in
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       the initial root table size constants.  See the comments in inftrees.h
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       for more information.
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       sym increments through all symbols, and the loop terminates when
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       all codes of length max, i.e. all codes, have been processed.  This
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       routine permits incomplete codes, so another loop after this one fills
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       in the rest of the decoding tables with invalid code markers.
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     */
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    /* set up for code type */
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    switch (type) {
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    case CODES:
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        base = extra = work;    /* dummy value--not used */
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        match = 20;
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        break;
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    case LENS:
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        base = lbase;
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        extra = lext;
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        match = 257;
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        break;
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    default:    /* DISTS */
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        base = dbase;
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        extra = dext;
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        match = 0;
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    }
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    /* initialize state for loop */
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    huff = 0;                   /* starting code */
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    sym = 0;                    /* starting code symbol */
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    len = min;                  /* starting code length */
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    next = *table;              /* current table to fill in */
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    curr = root;                /* current table index bits */
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    drop = 0;                   /* current bits to drop from code for index */
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    low = (unsigned)(-1);       /* trigger new sub-table when len > root */
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    used = 1U << root;          /* use root table entries */
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    mask = used - 1;            /* mask for comparing low */
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    /* check available table space */
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    if ((type == LENS && used > ENOUGH_LENS) ||
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        (type == DISTS && used > ENOUGH_DISTS))
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        return 1;
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    /* process all codes and make table entries */
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    for (;;) {
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        /* create table entry */
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        here.bits = (unsigned char)(len - drop);
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        if (work[sym] + 1U < match) {
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            here.op = (unsigned char)0;
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            here.val = work[sym];
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        }
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        else if (work[sym] >= match) {
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            here.op = (unsigned char)(extra[work[sym] - match]);
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            here.val = base[work[sym] - match];
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        }
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        else {
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            here.op = (unsigned char)(32 + 64);         /* end of block */
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            here.val = 0;
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        }
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        /* replicate for those indices with low len bits equal to huff */
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        incr = 1U << (len - drop);
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        fill = 1U << curr;
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        min = fill;                 /* save offset to next table */
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        do {
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            fill -= incr;
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            next[(huff >> drop) + fill] = here;
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        } while (fill != 0);
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        /* backwards increment the len-bit code huff */
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        incr = 1U << (len - 1);
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        while (huff & incr)
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            incr >>= 1;
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        if (incr != 0) {
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            huff &= incr - 1;
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            huff += incr;
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        }
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        else
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            huff = 0;
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        /* go to next symbol, update count, len */
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        sym++;
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        if (--(count[len]) == 0) {
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            if (len == max) break;
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            len = lens[work[sym]];
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        }
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        /* create new sub-table if needed */
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        if (len > root && (huff & mask) != low) {
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            /* if first time, transition to sub-tables */
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            if (drop == 0)
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                drop = root;
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            /* increment past last table */
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            next += min;            /* here min is 1 << curr */
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            /* determine length of next table */
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            curr = len - drop;
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            left = (int)(1 << curr);
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            while (curr + drop < max) {
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                left -= count[curr + drop];
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                if (left <= 0) break;
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                curr++;
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                left <<= 1;
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            }
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            /* check for enough space */
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            used += 1U << curr;
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            if ((type == LENS && used > ENOUGH_LENS) ||
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                (type == DISTS && used > ENOUGH_DISTS))
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                return 1;
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            /* point entry in root table to sub-table */
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            low = huff & mask;
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            (*table)[low].op = (unsigned char)curr;
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            (*table)[low].bits = (unsigned char)root;
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            (*table)[low].val = (unsigned short)(next - *table);
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        }
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    }
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    /* fill in remaining table entry if code is incomplete (guaranteed to have
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       at most one remaining entry, since if the code is incomplete, the
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       maximum code length that was allowed to get this far is one bit) */
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    if (huff != 0) {
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        here.op = (unsigned char)64;            /* invalid code marker */
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        here.bits = (unsigned char)(len - drop);
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        here.val = (unsigned short)0;
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        next[huff] = here;
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    }
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    /* set return parameters */
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    *table += used;
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    *bits = root;
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    return 0;
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}