| /* |
| * puff.c |
| * Copyright (C) 2002-2013 Mark Adler |
| * For conditions of distribution and use, see copyright notice in puff.h |
| * version 2.3, 21 Jan 2013 |
| * |
| * 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 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 |
| * 2.3 21 Jan 2013 - Check for invalid code length codes in dynamic blocks |
| */ |
| |
| #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 < 0) |
| return symbol; /* invalid symbol */ |
| 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; |
| } |