/* inftrees.c -- generate Huffman trees for efficient decoding | |

* Copyright (C) 1995-2017 Mark Adler | |

* For conditions of distribution and use, see copyright notice in zlib.h | |

*/ | |

#include "zutil.h" | |

#include "inftrees.h" | |

#define MAXBITS 15 | |

const char inflate_copyright[] = | |

" inflate 1.2.11 Copyright 1995-2017 Mark Adler "; | |

/* | |

If you use the zlib library in a product, an acknowledgment is welcome | |

in the documentation of your product. If for some reason you cannot | |

include such an acknowledgment, I would appreciate that you keep this | |

copyright string in the executable of your product. | |

*/ | |

/* | |

Build a 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 ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work) | |

codetype type; | |

unsigned short FAR *lens; | |

unsigned codes; | |

code FAR * FAR *table; | |

unsigned FAR *bits; | |

unsigned short FAR *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 */ | |

code here; /* table entry for duplication */ | |

code FAR *next; /* next available space in table */ | |

const unsigned short FAR *base; /* base value table to use */ | |

const unsigned short FAR *extra; /* extra bits table to use */ | |

unsigned match; /* use base and extra for symbol >= match */ | |

unsigned short count[MAXBITS+1]; /* number of codes of each length */ | |

unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ | |

static const unsigned short lbase[31] = { /* Length codes 257..285 base */ | |

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}; | |

static const unsigned short lext[31] = { /* Length codes 257..285 extra */ | |

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}; | |

static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ | |

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}; | |

static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ | |

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}; | |

/* | |

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 = (unsigned char)64; /* invalid code marker */ | |

here.bits = (unsigned char)1; | |

here.val = (unsigned short)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]]++] = (unsigned short)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 = lbase; | |

extra = lext; | |

match = 257; | |

break; | |

default: /* DISTS */ | |

base = dbase; | |

extra = dext; | |

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 = (unsigned char)(len - drop); | |

if (work[sym] + 1U < match) { | |

here.op = (unsigned char)0; | |

here.val = work[sym]; | |

} | |

else if (work[sym] >= match) { | |

here.op = (unsigned char)(extra[work[sym] - match]); | |

here.val = base[work[sym] - match]; | |

} | |

else { | |

here.op = (unsigned char)(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)(1 << 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 = (unsigned char)curr; | |

(*table)[low].bits = (unsigned char)root; | |

(*table)[low].val = (unsigned short)(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 = (unsigned char)64; /* invalid code marker */ | |

here.bits = (unsigned char)(len - drop); | |

here.val = (unsigned short)0; | |

next[huff] = here; | |

} | |

/* set return parameters */ | |

*table += used; | |

*bits = root; | |

return 0; | |

} |