/* | |

* puff.c | |

* Copyright (C) 2002-2010 Mark Adler | |

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

* version 2.2, 25 Apr 2010 | |

* | |

* puff.c is a simple inflate written to be an unambiguous way to specify the | |

* deflate format. It is not written for speed but rather simplicity. As a | |

* side benefit, this code might actually be useful when small code is more | |

* important than speed, such as bootstrap applications. For typical deflate | |

* data, zlib's inflate() is about four times as fast as puff(). zlib's | |

* inflate compiles to around 20K on my machine, whereas puff.c compiles to | |

* around 4K on my machine (a PowerPC using GNU cc). If the faster decode() | |

* function here is used, then puff() is only twice as slow as zlib's | |

* inflate(). | |

* | |

* All dynamically allocated memory comes from the stack. The stack required | |

* is less than 2K bytes. This code is compatible with 16-bit int's and | |

* assumes that long's are at least 32 bits. puff.c uses the short data type, | |

* assumed to be 16 bits, for arrays in order to to conserve memory. The code | |

* works whether integers are stored big endian or little endian. | |

* | |

* In the comments below are "Format notes" that describe the inflate process | |

* and document some of the less obvious aspects of the format. This source | |

* code is meant to supplement RFC 1951, which formally describes the deflate | |

* format: | |

* | |

* http://www.zlib.org/rfc-deflate.html | |

*/ | |

/* | |

* Change history: | |

* | |

* 1.0 10 Feb 2002 - First version | |

* 1.1 17 Feb 2002 - Clarifications of some comments and notes | |

* - Update puff() dest and source pointers on negative | |

* errors to facilitate debugging deflators | |

* - Remove longest from struct huffman -- not needed | |

* - Simplify offs[] index in construct() | |

* - Add input size and checking, using longjmp() to | |

* maintain easy readability | |

* - Use short data type for large arrays | |

* - Use pointers instead of long to specify source and | |

* destination sizes to avoid arbitrary 4 GB limits | |

* 1.2 17 Mar 2002 - Add faster version of decode(), doubles speed (!), | |

* but leave simple version for readabilty | |

* - Make sure invalid distances detected if pointers | |

* are 16 bits | |

* - Fix fixed codes table error | |

* - Provide a scanning mode for determining size of | |

* uncompressed data | |

* 1.3 20 Mar 2002 - Go back to lengths for puff() parameters [Gailly] | |

* - Add a puff.h file for the interface | |

* - Add braces in puff() for else do [Gailly] | |

* - Use indexes instead of pointers for readability | |

* 1.4 31 Mar 2002 - Simplify construct() code set check | |

* - Fix some comments | |

* - Add FIXLCODES #define | |

* 1.5 6 Apr 2002 - Minor comment fixes | |

* 1.6 7 Aug 2002 - Minor format changes | |

* 1.7 3 Mar 2003 - Added test code for distribution | |

* - Added zlib-like license | |

* 1.8 9 Jan 2004 - Added some comments on no distance codes case | |

* 1.9 21 Feb 2008 - Fix bug on 16-bit integer architectures [Pohland] | |

* - Catch missing end-of-block symbol error | |

* 2.0 25 Jul 2008 - Add #define to permit distance too far back | |

* - Add option in TEST code for puff to write the data | |

* - Add option in TEST code to skip input bytes | |

* - Allow TEST code to read from piped stdin | |

* 2.1 4 Apr 2010 - Avoid variable initialization for happier compilers | |

* - Avoid unsigned comparisons for even happier compilers | |

* 2.2 25 Apr 2010 - Fix bug in variable initializations [Oberhumer] | |

* - Add const where appropriate [Oberhumer] | |

* - Split if's and ?'s for coverage testing | |

* - Break out test code to separate file | |

* - Move NIL to puff.h | |

* - Allow incomplete code only if single code length is 1 | |

* - Add full code coverage test to Makefile | |

*/ | |

#include <setjmp.h> /* for setjmp(), longjmp(), and jmp_buf */ | |

#include "puff.h" /* prototype for puff() */ | |

#define local static /* for local function definitions */ | |

/* | |

* Maximums for allocations and loops. It is not useful to change these -- | |

* they are fixed by the deflate format. | |

*/ | |

#define MAXBITS 15 /* maximum bits in a code */ | |

#define MAXLCODES 286 /* maximum number of literal/length codes */ | |

#define MAXDCODES 30 /* maximum number of distance codes */ | |

#define MAXCODES (MAXLCODES+MAXDCODES) /* maximum codes lengths to read */ | |

#define FIXLCODES 288 /* number of fixed literal/length codes */ | |

/* input and output state */ | |

struct state { | |

/* output state */ | |

unsigned char *out; /* output buffer */ | |

unsigned long outlen; /* available space at out */ | |

unsigned long outcnt; /* bytes written to out so far */ | |

/* input state */ | |

const unsigned char *in; /* input buffer */ | |

unsigned long inlen; /* available input at in */ | |

unsigned long incnt; /* bytes read so far */ | |

int bitbuf; /* bit buffer */ | |

int bitcnt; /* number of bits in bit buffer */ | |

/* input limit error return state for bits() and decode() */ | |

jmp_buf env; | |

}; | |

/* | |

* Return need bits from the input stream. This always leaves less than | |

* eight bits in the buffer. bits() works properly for need == 0. | |

* | |

* Format notes: | |

* | |

* - Bits are stored in bytes from the least significant bit to the most | |

* significant bit. Therefore bits are dropped from the bottom of the bit | |

* buffer, using shift right, and new bytes are appended to the top of the | |

* bit buffer, using shift left. | |

*/ | |

local int bits(struct state *s, int need) | |

{ | |

long val; /* bit accumulator (can use up to 20 bits) */ | |

/* load at least need bits into val */ | |

val = s->bitbuf; | |

while (s->bitcnt < need) { | |

if (s->incnt == s->inlen) | |

longjmp(s->env, 1); /* out of input */ | |

val |= (long)(s->in[s->incnt++]) << s->bitcnt; /* load eight bits */ | |

s->bitcnt += 8; | |

} | |

/* drop need bits and update buffer, always zero to seven bits left */ | |

s->bitbuf = (int)(val >> need); | |

s->bitcnt -= need; | |

/* return need bits, zeroing the bits above that */ | |

return (int)(val & ((1L << need) - 1)); | |

} | |

/* | |

* Process a stored block. | |

* | |

* Format notes: | |

* | |

* - After the two-bit stored block type (00), the stored block length and | |

* stored bytes are byte-aligned for fast copying. Therefore any leftover | |

* bits in the byte that has the last bit of the type, as many as seven, are | |

* discarded. The value of the discarded bits are not defined and should not | |

* be checked against any expectation. | |

* | |

* - The second inverted copy of the stored block length does not have to be | |

* checked, but it's probably a good idea to do so anyway. | |

* | |

* - A stored block can have zero length. This is sometimes used to byte-align | |

* subsets of the compressed data for random access or partial recovery. | |

*/ | |

local int stored(struct state *s) | |

{ | |

unsigned len; /* length of stored block */ | |

/* discard leftover bits from current byte (assumes s->bitcnt < 8) */ | |

s->bitbuf = 0; | |

s->bitcnt = 0; | |

/* get length and check against its one's complement */ | |

if (s->incnt + 4 > s->inlen) | |

return 2; /* not enough input */ | |

len = s->in[s->incnt++]; | |

len |= s->in[s->incnt++] << 8; | |

if (s->in[s->incnt++] != (~len & 0xff) || | |

s->in[s->incnt++] != ((~len >> 8) & 0xff)) | |

return -2; /* didn't match complement! */ | |

/* copy len bytes from in to out */ | |

if (s->incnt + len > s->inlen) | |

return 2; /* not enough input */ | |

if (s->out != NIL) { | |

if (s->outcnt + len > s->outlen) | |

return 1; /* not enough output space */ | |

while (len--) | |

s->out[s->outcnt++] = s->in[s->incnt++]; | |

} | |

else { /* just scanning */ | |

s->outcnt += len; | |

s->incnt += len; | |

} | |

/* done with a valid stored block */ | |

return 0; | |

} | |

/* | |

* Huffman code decoding tables. count[1..MAXBITS] is the number of symbols of | |

* each length, which for a canonical code are stepped through in order. | |

* symbol[] are the symbol values in canonical order, where the number of | |

* entries is the sum of the counts in count[]. The decoding process can be | |

* seen in the function decode() below. | |

*/ | |

struct huffman { | |

short *count; /* number of symbols of each length */ | |

short *symbol; /* canonically ordered symbols */ | |

}; | |

/* | |

* Decode a code from the stream s using huffman table h. Return the symbol or | |

* a negative value if there is an error. If all of the lengths are zero, i.e. | |

* an empty code, or if the code is incomplete and an invalid code is received, | |

* then -10 is returned after reading MAXBITS bits. | |

* | |

* Format notes: | |

* | |

* - The codes as stored in the compressed data are bit-reversed relative to | |

* a simple integer ordering of codes of the same lengths. Hence below the | |

* bits are pulled from the compressed data one at a time and used to | |

* build the code value reversed from what is in the stream in order to | |

* permit simple integer comparisons for decoding. A table-based decoding | |

* scheme (as used in zlib) does not need to do this reversal. | |

* | |

* - The first code for the shortest length is all zeros. Subsequent codes of | |

* the same length are simply integer increments of the previous code. When | |

* moving up a length, a zero bit is appended to the code. For a complete | |

* code, the last code of the longest length will be all ones. | |

* | |

* - Incomplete codes are handled by this decoder, since they are permitted | |

* in the deflate format. See the format notes for fixed() and dynamic(). | |

*/ | |

#ifdef SLOW | |

local int decode(struct state *s, const struct huffman *h) | |

{ | |

int len; /* current number of bits in code */ | |

int code; /* len bits being decoded */ | |

int first; /* first code of length len */ | |

int count; /* number of codes of length len */ | |

int index; /* index of first code of length len in symbol table */ | |

code = first = index = 0; | |

for (len = 1; len <= MAXBITS; len++) { | |

code |= bits(s, 1); /* get next bit */ | |

count = h->count[len]; | |

if (code - count < first) /* if length len, return symbol */ | |

return h->symbol[index + (code - first)]; | |

index += count; /* else update for next length */ | |

first += count; | |

first <<= 1; | |

code <<= 1; | |

} | |

return -10; /* ran out of codes */ | |

} | |

/* | |

* A faster version of decode() for real applications of this code. It's not | |

* as readable, but it makes puff() twice as fast. And it only makes the code | |

* a few percent larger. | |

*/ | |

#else /* !SLOW */ | |

local int decode(struct state *s, const struct huffman *h) | |

{ | |

int len; /* current number of bits in code */ | |

int code; /* len bits being decoded */ | |

int first; /* first code of length len */ | |

int count; /* number of codes of length len */ | |

int index; /* index of first code of length len in symbol table */ | |

int bitbuf; /* bits from stream */ | |

int left; /* bits left in next or left to process */ | |

short *next; /* next number of codes */ | |

bitbuf = s->bitbuf; | |

left = s->bitcnt; | |

code = first = index = 0; | |

len = 1; | |

next = h->count + 1; | |

while (1) { | |

while (left--) { | |

code |= bitbuf & 1; | |

bitbuf >>= 1; | |

count = *next++; | |

if (code - count < first) { /* if length len, return symbol */ | |

s->bitbuf = bitbuf; | |

s->bitcnt = (s->bitcnt - len) & 7; | |

return h->symbol[index + (code - first)]; | |

} | |

index += count; /* else update for next length */ | |

first += count; | |

first <<= 1; | |

code <<= 1; | |

len++; | |

} | |

left = (MAXBITS+1) - len; | |

if (left == 0) | |

break; | |

if (s->incnt == s->inlen) | |

longjmp(s->env, 1); /* out of input */ | |

bitbuf = s->in[s->incnt++]; | |

if (left > 8) | |

left = 8; | |

} | |

return -10; /* ran out of codes */ | |

} | |

#endif /* SLOW */ | |

/* | |

* Given the list of code lengths length[0..n-1] representing a canonical | |

* Huffman code for n symbols, construct the tables required to decode those | |

* codes. Those tables are the number of codes of each length, and the symbols | |

* sorted by length, retaining their original order within each length. The | |

* return value is zero for a complete code set, negative for an over- | |

* subscribed code set, and positive for an incomplete code set. The tables | |

* can be used if the return value is zero or positive, but they cannot be used | |

* if the return value is negative. If the return value is zero, it is not | |

* possible for decode() using that table to return an error--any stream of | |

* enough bits will resolve to a symbol. If the return value is positive, then | |

* it is possible for decode() using that table to return an error for received | |

* codes past the end of the incomplete lengths. | |

* | |

* Not used by decode(), but used for error checking, h->count[0] is the number | |

* of the n symbols not in the code. So n - h->count[0] is the number of | |

* codes. This is useful for checking for incomplete codes that have more than | |

* one symbol, which is an error in a dynamic block. | |

* | |

* Assumption: for all i in 0..n-1, 0 <= length[i] <= MAXBITS | |

* This is assured by the construction of the length arrays in dynamic() and | |

* fixed() and is not verified by construct(). | |

* | |

* Format notes: | |

* | |

* - Permitted and expected examples of incomplete codes are one of the fixed | |

* codes and any code with a single symbol which in deflate is coded as one | |

* bit instead of zero bits. See the format notes for fixed() and dynamic(). | |

* | |

* - Within a given code length, the symbols are kept in ascending order for | |

* the code bits definition. | |

*/ | |

local int construct(struct huffman *h, const short *length, int n) | |

{ | |

int symbol; /* current symbol when stepping through length[] */ | |

int len; /* current length when stepping through h->count[] */ | |

int left; /* number of possible codes left of current length */ | |

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

/* count number of codes of each length */ | |

for (len = 0; len <= MAXBITS; len++) | |

h->count[len] = 0; | |

for (symbol = 0; symbol < n; symbol++) | |

(h->count[length[symbol]])++; /* assumes lengths are within bounds */ | |

if (h->count[0] == n) /* no codes! */ | |

return 0; /* complete, but decode() will fail */ | |

/* check for an over-subscribed or incomplete set of lengths */ | |

left = 1; /* one possible code of zero length */ | |

for (len = 1; len <= MAXBITS; len++) { | |

left <<= 1; /* one more bit, double codes left */ | |

left -= h->count[len]; /* deduct count from possible codes */ | |

if (left < 0) | |

return left; /* over-subscribed--return negative */ | |

} /* left > 0 means incomplete */ | |

/* generate offsets into symbol table for each length for sorting */ | |

offs[1] = 0; | |

for (len = 1; len < MAXBITS; len++) | |

offs[len + 1] = offs[len] + h->count[len]; | |

/* | |

* put symbols in table sorted by length, by symbol order within each | |

* length | |

*/ | |

for (symbol = 0; symbol < n; symbol++) | |

if (length[symbol] != 0) | |

h->symbol[offs[length[symbol]]++] = symbol; | |

/* return zero for complete set, positive for incomplete set */ | |

return left; | |

} | |

/* | |

* Decode literal/length and distance codes until an end-of-block code. | |

* | |

* Format notes: | |

* | |

* - Compressed data that is after the block type if fixed or after the code | |

* description if dynamic is a combination of literals and length/distance | |

* pairs terminated by and end-of-block code. Literals are simply Huffman | |

* coded bytes. A length/distance pair is a coded length followed by a | |

* coded distance to represent a string that occurs earlier in the | |

* uncompressed data that occurs again at the current location. | |

* | |

* - Literals, lengths, and the end-of-block code are combined into a single | |

* code of up to 286 symbols. They are 256 literals (0..255), 29 length | |

* symbols (257..285), and the end-of-block symbol (256). | |

* | |

* - There are 256 possible lengths (3..258), and so 29 symbols are not enough | |

* to represent all of those. Lengths 3..10 and 258 are in fact represented | |

* by just a length symbol. Lengths 11..257 are represented as a symbol and | |

* some number of extra bits that are added as an integer to the base length | |

* of the length symbol. The number of extra bits is determined by the base | |

* length symbol. These are in the static arrays below, lens[] for the base | |

* lengths and lext[] for the corresponding number of extra bits. | |

* | |

* - The reason that 258 gets its own symbol is that the longest length is used | |

* often in highly redundant files. Note that 258 can also be coded as the | |

* base value 227 plus the maximum extra value of 31. While a good deflate | |

* should never do this, it is not an error, and should be decoded properly. | |

* | |

* - If a length is decoded, including its extra bits if any, then it is | |

* followed a distance code. There are up to 30 distance symbols. Again | |

* there are many more possible distances (1..32768), so extra bits are added | |

* to a base value represented by the symbol. The distances 1..4 get their | |

* own symbol, but the rest require extra bits. The base distances and | |

* corresponding number of extra bits are below in the static arrays dist[] | |

* and dext[]. | |

* | |

* - Literal bytes are simply written to the output. A length/distance pair is | |

* an instruction to copy previously uncompressed bytes to the output. The | |

* copy is from distance bytes back in the output stream, copying for length | |

* bytes. | |

* | |

* - Distances pointing before the beginning of the output data are not | |

* permitted. | |

* | |

* - Overlapped copies, where the length is greater than the distance, are | |

* allowed and common. For example, a distance of one and a length of 258 | |

* simply copies the last byte 258 times. A distance of four and a length of | |

* twelve copies the last four bytes three times. A simple forward copy | |

* ignoring whether the length is greater than the distance or not implements | |

* this correctly. You should not use memcpy() since its behavior is not | |

* defined for overlapped arrays. You should not use memmove() or bcopy() | |

* since though their behavior -is- defined for overlapping arrays, it is | |

* defined to do the wrong thing in this case. | |

*/ | |

local int codes(struct state *s, | |

const struct huffman *lencode, | |

const struct huffman *distcode) | |

{ | |

int symbol; /* decoded symbol */ | |

int len; /* length for copy */ | |

unsigned dist; /* distance for copy */ | |

static const short lens[29] = { /* Size base for length codes 257..285 */ | |

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}; | |

static const short lext[29] = { /* Extra bits for length codes 257..285 */ | |

0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, | |

3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0}; | |

static const short dists[30] = { /* Offset base for distance codes 0..29 */ | |

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}; | |

static const short dext[30] = { /* Extra bits for distance codes 0..29 */ | |

0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, | |

7, 7, 8, 8, 9, 9, 10, 10, 11, 11, | |

12, 12, 13, 13}; | |

/* decode literals and length/distance pairs */ | |

do { | |

symbol = decode(s, lencode); | |

if (symbol < 0) | |

return symbol; /* invalid symbol */ | |

if (symbol < 256) { /* literal: symbol is the byte */ | |

/* write out the literal */ | |

if (s->out != NIL) { | |

if (s->outcnt == s->outlen) | |

return 1; | |

s->out[s->outcnt] = symbol; | |

} | |

s->outcnt++; | |

} | |

else if (symbol > 256) { /* length */ | |

/* get and compute length */ | |

symbol -= 257; | |

if (symbol >= 29) | |

return -10; /* invalid fixed code */ | |

len = lens[symbol] + bits(s, lext[symbol]); | |

/* get and check distance */ | |

symbol = decode(s, distcode); | |

if (symbol < 0) | |

return symbol; /* invalid symbol */ | |

dist = dists[symbol] + bits(s, dext[symbol]); | |

#ifndef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR | |

if (dist > s->outcnt) | |

return -11; /* distance too far back */ | |

#endif | |

/* copy length bytes from distance bytes back */ | |

if (s->out != NIL) { | |

if (s->outcnt + len > s->outlen) | |

return 1; | |

while (len--) { | |

s->out[s->outcnt] = | |

#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR | |

dist > s->outcnt ? | |

0 : | |

#endif | |

s->out[s->outcnt - dist]; | |

s->outcnt++; | |

} | |

} | |

else | |

s->outcnt += len; | |

} | |

} while (symbol != 256); /* end of block symbol */ | |

/* done with a valid fixed or dynamic block */ | |

return 0; | |

} | |

/* | |

* Process a fixed codes block. | |

* | |

* Format notes: | |

* | |

* - This block type can be useful for compressing small amounts of data for | |

* which the size of the code descriptions in a dynamic block exceeds the | |

* benefit of custom codes for that block. For fixed codes, no bits are | |

* spent on code descriptions. Instead the code lengths for literal/length | |

* codes and distance codes are fixed. The specific lengths for each symbol | |

* can be seen in the "for" loops below. | |

* | |

* - The literal/length code is complete, but has two symbols that are invalid | |

* and should result in an error if received. This cannot be implemented | |

* simply as an incomplete code since those two symbols are in the "middle" | |

* of the code. They are eight bits long and the longest literal/length\ | |

* code is nine bits. Therefore the code must be constructed with those | |

* symbols, and the invalid symbols must be detected after decoding. | |

* | |

* - The fixed distance codes also have two invalid symbols that should result | |

* in an error if received. Since all of the distance codes are the same | |

* length, this can be implemented as an incomplete code. Then the invalid | |

* codes are detected while decoding. | |

*/ | |

local int fixed(struct state *s) | |

{ | |

static int virgin = 1; | |

static short lencnt[MAXBITS+1], lensym[FIXLCODES]; | |

static short distcnt[MAXBITS+1], distsym[MAXDCODES]; | |

static struct huffman lencode, distcode; | |

/* build fixed huffman tables if first call (may not be thread safe) */ | |

if (virgin) { | |

int symbol; | |

short lengths[FIXLCODES]; | |

/* construct lencode and distcode */ | |

lencode.count = lencnt; | |

lencode.symbol = lensym; | |

distcode.count = distcnt; | |

distcode.symbol = distsym; | |

/* literal/length table */ | |

for (symbol = 0; symbol < 144; symbol++) | |

lengths[symbol] = 8; | |

for (; symbol < 256; symbol++) | |

lengths[symbol] = 9; | |

for (; symbol < 280; symbol++) | |

lengths[symbol] = 7; | |

for (; symbol < FIXLCODES; symbol++) | |

lengths[symbol] = 8; | |

construct(&lencode, lengths, FIXLCODES); | |

/* distance table */ | |

for (symbol = 0; symbol < MAXDCODES; symbol++) | |

lengths[symbol] = 5; | |

construct(&distcode, lengths, MAXDCODES); | |

/* do this just once */ | |

virgin = 0; | |

} | |

/* decode data until end-of-block code */ | |

return codes(s, &lencode, &distcode); | |

} | |

/* | |

* Process a dynamic codes block. | |

* | |

* Format notes: | |

* | |

* - A dynamic block starts with a description of the literal/length and | |

* distance codes for that block. New dynamic blocks allow the compressor to | |

* rapidly adapt to changing data with new codes optimized for that data. | |

* | |

* - The codes used by the deflate format are "canonical", which means that | |

* the actual bits of the codes are generated in an unambiguous way simply | |

* from the number of bits in each code. Therefore the code descriptions | |

* are simply a list of code lengths for each symbol. | |

* | |

* - The code lengths are stored in order for the symbols, so lengths are | |

* provided for each of the literal/length symbols, and for each of the | |

* distance symbols. | |

* | |

* - If a symbol is not used in the block, this is represented by a zero as | |

* as the code length. This does not mean a zero-length code, but rather | |

* that no code should be created for this symbol. There is no way in the | |

* deflate format to represent a zero-length code. | |

* | |

* - The maximum number of bits in a code is 15, so the possible lengths for | |

* any code are 1..15. | |

* | |

* - The fact that a length of zero is not permitted for a code has an | |

* interesting consequence. Normally if only one symbol is used for a given | |

* code, then in fact that code could be represented with zero bits. However | |

* in deflate, that code has to be at least one bit. So for example, if | |

* only a single distance base symbol appears in a block, then it will be | |

* represented by a single code of length one, in particular one 0 bit. This | |

* is an incomplete code, since if a 1 bit is received, it has no meaning, | |

* and should result in an error. So incomplete distance codes of one symbol | |

* should be permitted, and the receipt of invalid codes should be handled. | |

* | |

* - It is also possible to have a single literal/length code, but that code | |

* must be the end-of-block code, since every dynamic block has one. This | |

* is not the most efficient way to create an empty block (an empty fixed | |

* block is fewer bits), but it is allowed by the format. So incomplete | |

* literal/length codes of one symbol should also be permitted. | |

* | |

* - If there are only literal codes and no lengths, then there are no distance | |

* codes. This is represented by one distance code with zero bits. | |

* | |

* - The list of up to 286 length/literal lengths and up to 30 distance lengths | |

* are themselves compressed using Huffman codes and run-length encoding. In | |

* the list of code lengths, a 0 symbol means no code, a 1..15 symbol means | |

* that length, and the symbols 16, 17, and 18 are run-length instructions. | |

* Each of 16, 17, and 18 are follwed by extra bits to define the length of | |

* the run. 16 copies the last length 3 to 6 times. 17 represents 3 to 10 | |

* zero lengths, and 18 represents 11 to 138 zero lengths. Unused symbols | |

* are common, hence the special coding for zero lengths. | |

* | |

* - The symbols for 0..18 are Huffman coded, and so that code must be | |

* described first. This is simply a sequence of up to 19 three-bit values | |

* representing no code (0) or the code length for that symbol (1..7). | |

* | |

* - A dynamic block starts with three fixed-size counts from which is computed | |

* the number of literal/length code lengths, the number of distance code | |

* lengths, and the number of code length code lengths (ok, you come up with | |

* a better name!) in the code descriptions. For the literal/length and | |

* distance codes, lengths after those provided are considered zero, i.e. no | |

* code. The code length code lengths are received in a permuted order (see | |

* the order[] array below) to make a short code length code length list more | |

* likely. As it turns out, very short and very long codes are less likely | |

* to be seen in a dynamic code description, hence what may appear initially | |

* to be a peculiar ordering. | |

* | |

* - Given the number of literal/length code lengths (nlen) and distance code | |

* lengths (ndist), then they are treated as one long list of nlen + ndist | |

* code lengths. Therefore run-length coding can and often does cross the | |

* boundary between the two sets of lengths. | |

* | |

* - So to summarize, the code description at the start of a dynamic block is | |

* three counts for the number of code lengths for the literal/length codes, | |

* the distance codes, and the code length codes. This is followed by the | |

* code length code lengths, three bits each. This is used to construct the | |

* code length code which is used to read the remainder of the lengths. Then | |

* the literal/length code lengths and distance lengths are read as a single | |

* set of lengths using the code length codes. Codes are constructed from | |

* the resulting two sets of lengths, and then finally you can start | |

* decoding actual compressed data in the block. | |

* | |

* - For reference, a "typical" size for the code description in a dynamic | |

* block is around 80 bytes. | |

*/ | |

local int dynamic(struct state *s) | |

{ | |

int nlen, ndist, ncode; /* number of lengths in descriptor */ | |

int index; /* index of lengths[] */ | |

int err; /* construct() return value */ | |

short lengths[MAXCODES]; /* descriptor code lengths */ | |

short lencnt[MAXBITS+1], lensym[MAXLCODES]; /* lencode memory */ | |

short distcnt[MAXBITS+1], distsym[MAXDCODES]; /* distcode memory */ | |

struct huffman lencode, distcode; /* length and distance codes */ | |

static const short order[19] = /* permutation of code length codes */ | |

{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}; | |

/* construct lencode and distcode */ | |

lencode.count = lencnt; | |

lencode.symbol = lensym; | |

distcode.count = distcnt; | |

distcode.symbol = distsym; | |

/* get number of lengths in each table, check lengths */ | |

nlen = bits(s, 5) + 257; | |

ndist = bits(s, 5) + 1; | |

ncode = bits(s, 4) + 4; | |

if (nlen > MAXLCODES || ndist > MAXDCODES) | |

return -3; /* bad counts */ | |

/* read code length code lengths (really), missing lengths are zero */ | |

for (index = 0; index < ncode; index++) | |

lengths[order[index]] = bits(s, 3); | |

for (; index < 19; index++) | |

lengths[order[index]] = 0; | |

/* build huffman table for code lengths codes (use lencode temporarily) */ | |

err = construct(&lencode, lengths, 19); | |

if (err != 0) /* require complete code set here */ | |

return -4; | |

/* read length/literal and distance code length tables */ | |

index = 0; | |

while (index < nlen + ndist) { | |

int symbol; /* decoded value */ | |

int len; /* last length to repeat */ | |

symbol = decode(s, &lencode); | |

if (symbol < 16) /* length in 0..15 */ | |

lengths[index++] = symbol; | |

else { /* repeat instruction */ | |

len = 0; /* assume repeating zeros */ | |

if (symbol == 16) { /* repeat last length 3..6 times */ | |

if (index == 0) | |

return -5; /* no last length! */ | |

len = lengths[index - 1]; /* last length */ | |

symbol = 3 + bits(s, 2); | |

} | |

else if (symbol == 17) /* repeat zero 3..10 times */ | |

symbol = 3 + bits(s, 3); | |

else /* == 18, repeat zero 11..138 times */ | |

symbol = 11 + bits(s, 7); | |

if (index + symbol > nlen + ndist) | |

return -6; /* too many lengths! */ | |

while (symbol--) /* repeat last or zero symbol times */ | |

lengths[index++] = len; | |

} | |

} | |

/* check for end-of-block code -- there better be one! */ | |

if (lengths[256] == 0) | |

return -9; | |

/* build huffman table for literal/length codes */ | |

err = construct(&lencode, lengths, nlen); | |

if (err && (err < 0 || nlen != lencode.count[0] + lencode.count[1])) | |

return -7; /* incomplete code ok only for single length 1 code */ | |

/* build huffman table for distance codes */ | |

err = construct(&distcode, lengths + nlen, ndist); | |

if (err && (err < 0 || ndist != distcode.count[0] + distcode.count[1])) | |

return -8; /* incomplete code ok only for single length 1 code */ | |

/* decode data until end-of-block code */ | |

return codes(s, &lencode, &distcode); | |

} | |

/* | |

* Inflate source to dest. On return, destlen and sourcelen are updated to the | |

* size of the uncompressed data and the size of the deflate data respectively. | |

* On success, the return value of puff() is zero. If there is an error in the | |

* source data, i.e. it is not in the deflate format, then a negative value is | |

* returned. If there is not enough input available or there is not enough | |

* output space, then a positive error is returned. In that case, destlen and | |

* sourcelen are not updated to facilitate retrying from the beginning with the | |

* provision of more input data or more output space. In the case of invalid | |

* inflate data (a negative error), the dest and source pointers are updated to | |

* facilitate the debugging of deflators. | |

* | |

* puff() also has a mode to determine the size of the uncompressed output with | |

* no output written. For this dest must be (unsigned char *)0. In this case, | |

* the input value of *destlen is ignored, and on return *destlen is set to the | |

* size of the uncompressed output. | |

* | |

* The return codes are: | |

* | |

* 2: available inflate data did not terminate | |

* 1: output space exhausted before completing inflate | |

* 0: successful inflate | |

* -1: invalid block type (type == 3) | |

* -2: stored block length did not match one's complement | |

* -3: dynamic block code description: too many length or distance codes | |

* -4: dynamic block code description: code lengths codes incomplete | |

* -5: dynamic block code description: repeat lengths with no first length | |

* -6: dynamic block code description: repeat more than specified lengths | |

* -7: dynamic block code description: invalid literal/length code lengths | |

* -8: dynamic block code description: invalid distance code lengths | |

* -9: dynamic block code description: missing end-of-block code | |

* -10: invalid literal/length or distance code in fixed or dynamic block | |

* -11: distance is too far back in fixed or dynamic block | |

* | |

* Format notes: | |

* | |

* - Three bits are read for each block to determine the kind of block and | |

* whether or not it is the last block. Then the block is decoded and the | |

* process repeated if it was not the last block. | |

* | |

* - The leftover bits in the last byte of the deflate data after the last | |

* block (if it was a fixed or dynamic block) are undefined and have no | |

* expected values to check. | |

*/ | |

int puff(unsigned char *dest, /* pointer to destination pointer */ | |

unsigned long *destlen, /* amount of output space */ | |

const unsigned char *source, /* pointer to source data pointer */ | |

unsigned long *sourcelen) /* amount of input available */ | |

{ | |

struct state s; /* input/output state */ | |

int last, type; /* block information */ | |

int err; /* return value */ | |

/* initialize output state */ | |

s.out = dest; | |

s.outlen = *destlen; /* ignored if dest is NIL */ | |

s.outcnt = 0; | |

/* initialize input state */ | |

s.in = source; | |

s.inlen = *sourcelen; | |

s.incnt = 0; | |

s.bitbuf = 0; | |

s.bitcnt = 0; | |

/* return if bits() or decode() tries to read past available input */ | |

if (setjmp(s.env) != 0) /* if came back here via longjmp() */ | |

err = 2; /* then skip do-loop, return error */ | |

else { | |

/* process blocks until last block or error */ | |

do { | |

last = bits(&s, 1); /* one if last block */ | |

type = bits(&s, 2); /* block type 0..3 */ | |

err = type == 0 ? | |

stored(&s) : | |

(type == 1 ? | |

fixed(&s) : | |

(type == 2 ? | |

dynamic(&s) : | |

-1)); /* type == 3, invalid */ | |

if (err != 0) | |

break; /* return with error */ | |

} while (!last); | |

} | |

/* update the lengths and return */ | |

if (err <= 0) { | |

*destlen = s.outcnt; | |

*sourcelen = s.incnt; | |

} | |

return err; | |

} |