cosmopolitan/third_party/zlib/inftrees.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=4 sts=4 sw=4 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 1995-2017 Mark Adler                                               │
│ Use of this source code is governed by the BSD-style licenses that can       │
│ be found in the third_party/zlib/LICENSE file.                               │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "third_party/zlib/inftrees.h"
#include "third_party/zlib/zutil.h"

asm(".ident\t\"\\n\\n\
inflate 1.2.11 (zlib License)\\n\
Copyright 1995-2017 Mark Adler\\n\
Invented 1990 Phillip Walter Katz\"");

/**
 * @fileoverview Generate Huffman trees for efficient decoding.
 */

#define MAXBITS 15

/* Length codes 257..285 base */
static const uint16_t kZlibDeflateLbase[31] = {
    3,  4,  5,  6,  7,  8,  9,  10,  11,  13,  15,  17,  19,  23, 27, 31,
    35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0,  0};

/* Length codes 257..285 extra */
static const uint16_t kZlibDeflateLext[31] = {
    16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
    19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 77, 202};

/* Distance codes 0..29 base */
static const uint16_t kZlibDeflateDbase[32] = {
    1,    2,    3,    4,    5,    7,     9,     13,    17,  25,   33,
    49,   65,   97,   129,  193,  257,   385,   513,   769, 1025, 1537,
    2049, 3073, 4097, 6145, 8193, 12289, 16385, 24577, 0,   0};

/* Distance codes 0..29 extra */
static const uint16_t kZlibDeflateDext[32] = {
    16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
    23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 28, 28, 29, 29, 64, 64};

/**
 * Builds set of tables to decode the provided canonical Huffman code.
 * The code lengths are lens[0..codes-1]. The result starts at *table,
 * whose indices are 0..2^bits-1. work is a writable array of at least
 * lens shorts, which is used as a work area. type is the type of code
 * to be generated, CODES, LENS, or DISTS. On return, zero is success,
 * -1 is an invalid code, and +1 means that ENOUGH isn't enough. table
 * on return points to the next available entry's address. bits is the
 * requested root table index bits, and on return it is the actual root
 * table index bits. It will differ if the request is greater than the
 * longest code or if it is less than the shortest code.
 */
int inflate_table(zcodetype type, uint16_t *lens, unsigned codes,
                  struct zcode **table, unsigned *bits, uint16_t *work) {
  unsigned len;                /* a code's length in bits */
  unsigned sym;                /* index of code symbols */
  unsigned min, max;           /* minimum and maximum code lengths */
  unsigned root;               /* number of index bits for root table */
  unsigned curr;               /* number of index bits for current table */
  unsigned drop;               /* code bits to drop for sub-table */
  int left;                    /* number of prefix codes available */
  unsigned used;               /* code entries in table used */
  unsigned huff;               /* Huffman code */
  unsigned incr;               /* for incrementing code, index */
  unsigned fill;               /* index for replicating entries */
  unsigned low;                /* low bits for current root entry */
  unsigned mask;               /* mask for low root bits */
  struct zcode here;           /* table entry for duplication */
  struct zcode *next;          /* next available space in table */
  const uint16_t *base;        /* base value table to use */
  const uint16_t *extra;       /* extra bits table to use */
  unsigned match;              /* use base and extra for symbol >= match */
  uint16_t count[MAXBITS + 1]; /* number of codes of each length */
  uint16_t offs[MAXBITS + 1];  /* offsets in table for each length */

  /*
     Process a set of code lengths to create a canonical Huffman code.  The
     code lengths are lens[0..codes-1].  Each length corresponds to the
     symbols 0..codes-1.  The Huffman code is generated by first sorting the
     symbols by length from short to long, and retaining the symbol order
     for codes with equal lengths.  Then the code starts with all zero bits
     for the first code of the shortest length, and the codes are integer
     increments for the same length, and zeros are appended as the length
     increases.  For the deflate format, these bits are stored backwards
     from their more natural integer increment ordering, and so when the
     decoding tables are built in the large loop below, the integer codes
     are incremented backwards.

     This routine assumes, but does not check, that all of the entries in
     lens[] are in the range 0..MAXBITS.  The caller must assure this.
     1..MAXBITS is interpreted as that code length.  zero means that that
     symbol does not occur in this code.

     The codes are sorted by computing a count of codes for each length,
     creating from that a table of starting indices for each length in the
     sorted table, and then entering the symbols in order in the sorted
     table.  The sorted table is work[], with that space being provided by
     the caller.

     The length counts are used for other purposes as well, i.e. finding
     the minimum and maximum length codes, determining if there are any
     codes at all, checking for a valid set of lengths, and looking ahead
     at length counts to determine sub-table sizes when building the
     decoding tables.
   */

  /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
  for (len = 0; len <= MAXBITS; len++) count[len] = 0;
  for (sym = 0; sym < codes; sym++) count[lens[sym]]++;

  /* bound code lengths, force root to be within code lengths */
  root = *bits;
  for (max = MAXBITS; max >= 1; max--) {
    if (count[max] != 0) break;
  }
  if (root > max) root = max;
  if (max == 0) {          /* no symbols to code at all */
    here.op = (uint8_t)64; /* invalid code marker */
    here.bits = (uint8_t)1;
    here.val = (uint16_t)0;
    *(*table)++ = here; /* make a table to force an error */
    *(*table)++ = here;
    *bits = 1;
    return 0; /* no symbols, but wait for decoding to report error */
  }
  for (min = 1; min < max; min++)
    if (count[min] != 0) break;
  if (root < min) root = min;

  /* check for an over-subscribed or incomplete set of lengths */
  left = 1;
  for (len = 1; len <= MAXBITS; len++) {
    left <<= 1;
    left -= count[len];
    if (left < 0) return -1; /* over-subscribed */
  }
  if (left > 0 && (type == CODES || max != 1)) return -1; /* incomplete set */

  /* generate offsets into symbol table for each length for sorting */
  offs[1] = 0;
  for (len = 1; len < MAXBITS; len++) {
    offs[len + 1] = offs[len] + count[len];
  }

  /* sort symbols by length, by symbol order within each length */
  for (sym = 0; sym < codes; sym++) {
    if (lens[sym] != 0) work[offs[lens[sym]]++] = (uint16_t)sym;
  }

  /*
    Create and fill in decoding tables. In this loop, the table being
    filled is at next and has curr index bits. The code being used is
    huff with length len. That code is converted to an index by dropping
    drop bits off of the bottom. For codes where len is less than drop +
    curr, those top drop + curr - len bits are incremented through all
    values to fill the table with replicated entries.

    root is the number of index bits for the root table. When len
    exceeds root, sub-tables are created pointed to by the root entry
    with an index of the low root bits of huff. This is saved in low to
    check for when a new sub-table should be started. drop is zero when
    the root table is being filled, and drop is root when sub-tables are
    being filled.

    When a new sub-table is needed, it is necessary to look ahead in the
    code lengths to determine what size sub-table is needed. The length
    counts are used for this, and so count[] is decremented as codes are
    entered in the tables.

    used keeps track of how many table entries have been allocated from
    the provided *table space. It is checked for LENS and DIST tables
    against the constants ENOUGH_LENS and ENOUGH_DISTS to guard against
    changes in the initial root table size constants. See the comments
    in inftrees.h for more information.

    sym increments through all symbols, and the loop terminates when all
    codes of length max, i.e. all codes, have been processed. This
    routine permits incomplete codes, so another loop after this one
    fills in the rest of the decoding tables with invalid code markers.
  */

  /* set up for code type */
  switch (type) {
    case CODES:
      base = extra = work; /* dummy value--not used */
      match = 20;
      break;
    case LENS:
      base = kZlibDeflateLbase;
      extra = kZlibDeflateLext;
      match = 257;
      break;
    default: /* DISTS */
      base = kZlibDeflateDbase;
      extra = kZlibDeflateDext;
      match = 0;
  }

  /* initialize state for loop */
  huff = 0;             /* starting code */
  sym = 0;              /* starting code symbol */
  len = min;            /* starting code length */
  next = *table;        /* current table to fill in */
  curr = root;          /* current table index bits */
  drop = 0;             /* current bits to drop from code for index */
  low = (unsigned)(-1); /* trigger new sub-table when len > root */
  used = 1U << root;    /* use root table entries */
  mask = used - 1;      /* mask for comparing low */

  /* check available table space */
  if ((type == LENS && used > ENOUGH_LENS) ||
      (type == DISTS && used > ENOUGH_DISTS)) {
    return 1;
  }

  /* process all codes and make table entries */
  for (;;) {
    /* create table entry */
    here.bits = (uint8_t)(len - drop);
    if (work[sym] + 1U < match) {
      here.op = (uint8_t)0;
      here.val = work[sym];
    } else if (work[sym] >= match) {
      here.op = (uint8_t)(extra[work[sym] - match]);
      here.val = base[work[sym] - match];
    } else {
      here.op = (uint8_t)(32 + 64); /* end of block */
      here.val = 0;
    }

    /* replicate for those indices with low len bits equal to huff */
    incr = 1U << (len - drop);
    fill = 1U << curr;
    min = fill; /* save offset to next table */
    do {
      fill -= incr;
      next[(huff >> drop) + fill] = here;
    } while (fill != 0);

    /* backwards increment the len-bit code huff */
    incr = 1U << (len - 1);
    while (huff & incr) incr >>= 1;
    if (incr != 0) {
      huff &= incr - 1;
      huff += incr;
    } else
      huff = 0;

    /* go to next symbol, update count, len */
    sym++;
    if (--(count[len]) == 0) {
      if (len == max) break;
      len = lens[work[sym]];
    }

    /* create new sub-table if needed */
    if (len > root && (huff & mask) != low) {
      /* if first time, transition to sub-tables */
      if (drop == 0) drop = root;

      /* increment past last table */
      next += min; /* here min is 1 << curr */

      /* determine length of next table */
      curr = len - drop;
      left = (int)(1u << curr);
      while (curr + drop < max) {
        left -= count[curr + drop];
        if (left <= 0) break;
        curr++;
        left <<= 1;
      }

      /* check for enough space */
      used += 1U << curr;
      if ((type == LENS && used > ENOUGH_LENS) ||
          (type == DISTS && used > ENOUGH_DISTS)) {
        return 1;
      }

      /* point entry in root table to sub-table */
      low = huff & mask;
      (*table)[low].op = (uint8_t)curr;
      (*table)[low].bits = (uint8_t)root;
      (*table)[low].val = (uint16_t)(next - *table);
    }
  }

  /* fill in remaining table entry if code is incomplete (guaranteed to have
     at most one remaining entry, since if the code is incomplete, the
     maximum code length that was allowed to get this far is one bit) */
  if (huff != 0) {
    here.op = (uint8_t)64; /* invalid code marker */
    here.bits = (uint8_t)(len - drop);
    here.val = (uint16_t)0;
    next[huff] = here;
  }

  /* set return parameters */
  *table += used;
  *bits = root;
  return 0;
}