/* blast.c

 * Copyright (C) 2003 Mark Adler

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

 * version 1.1, 16 Feb 2003

 *

 * blast.c decompresses data compressed by the PKWare Compression Library.

 * This function provides functionality similar to the explode() function of

 * the PKWare library, hence the name "blast".

 *

 * This decompressor is based on the excellent format description provided by

 * Ben Rudiak-Gould in comp.compression on August 13, 2001.  Interestingly, the

 * example Ben provided in the post is incorrect.  The distance 110001 should

 * instead be 111000.  When corrected, the example byte stream becomes:

 *

 *    00 04 82 24 25 8f 80 7f

 *

 * which decompresses to "AIAIAIAIAIAIA" (without the quotes).

 */

/*

 * Change history:

 *

 * 1.0  12 Feb 2003     - First version

 * 1.1  16 Feb 2003     - Fixed distance check for > 4 GB uncompressed data

 */

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

#include "blast.h"              /* prototype for blast() */

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

#define MAXBITS 13              /* maximum code length */

#define MAXWIN 4096             /* maximum window size */

/* input and output state */

struct state {

    /* input state */

    blast_in infun;             /* input function provided by user */

    void *inhow;                /* opaque information passed to infun() */

    unsigned char *in;          /* next input location */

    unsigned left;              /* available input at in */

    int bitbuf;                 /* bit buffer */

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

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

    jmp_buf env;

    /* output state */

    blast_out outfun;           /* output function provided by user */

    void *outhow;               /* opaque information passed to outfun() */

    unsigned next;              /* index of next write location in out[] */

    int first;                  /* true to check distances (for first 4K) */

    unsigned char out[MAXWIN];  /* output buffer and sliding window */

};

/*

 * 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)

{

    int val;            /* bit accumulator */

    /* load at least need bits into val */

    val = s->bitbuf;

    while (s->bitcnt < need) {

        if (s->left == 0) {

            s->left = s->infun(s->inhow, &(s->in));

            if (s->left == 0) longjmp(s->env, 1);       /* out of input */

        }

        val |= (int)(*(s->in)++) << s->bitcnt;          /* load eight bits */

        s->left--;

        s->bitcnt += 8;

    }

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

    s->bitbuf = val >> need;

    s->bitcnt -= need;

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

    return val & ((1 << need) - 1);

}

/*

 * 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 -9 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.

 *

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

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

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

 *   code, the last code of the longest length will be all zeros.  To support

 *   this ordering, the bits pulled during decoding are inverted to apply the

 *   more "natural" ordering starting with all zeros and incrementing.

 */

local int decode(struct state *s, 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) ^ 1;   /* invert code */

            bitbuf >>= 1;

            count = *next++;

            if (code < first + count) { /* 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->left == 0) {

            s->left = s->infun(s->inhow, &(s->in));

            if (s->left == 0) longjmp(s->env, 1);       /* out of input */

        }

        bitbuf = *(s->in)++;

        s->left--;

        if (left > 8) left = 8;

    }

    return -9;                          /* ran out of codes */

}

/*

 * Given a list of repeated code lengths rep[0..n-1], where each byte is a

 * count (high four bits + 1) and a code length (low four bits), generate the

 * list of code lengths.  This compaction reduces the size of the object code.

 * Then 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.

 */

local int construct(struct huffman *h, const unsigned char *rep, 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 */

    short length[256];  /* code lengths */

    /* convert compact repeat counts into symbol bit length list */

    symbol = 0;

    do {

        len = *rep++;

        left = (len >> 4) + 1;

        len &= 15;

        do {

            length[symbol++] = len;

        } while (--left);

    } while (--n);

    n = symbol;

    /* 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 PKWare Compression Library stream.

 *

 * Format notes:

 *

 * - First byte is 0 if literals are uncoded or 1 if they are coded.  Second

 *   byte is 4, 5, or 6 for the number of extra bits in the distance code.

 *   This is the base-2 logarithm of the dictionary size minus six.

 *

 * - Compressed data is a combination of literals and length/distance pairs

 *   terminated by an end code.  Literals are either Huffman coded or

 *   uncoded 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.

 *

 * - A bit preceding a literal or length/distance pair indicates which comes

 *   next, 0 for literals, 1 for length/distance.

 *

 * - If literals are uncoded, then the next eight bits are the literal, in the

 *   normal bit order in th stream, i.e. no bit-reversal is needed. Similarly,

 *   no bit reversal is needed for either the length extra bits or the distance

 *   extra bits.

 *

 * - 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 518

 *   simply copies the last byte 518 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.

 */

local int decomp(struct state *s)

{

    int lit;            /* true if literals are coded */

    int dict;           /* log2(dictionary size) - 6 */

    int symbol;         /* decoded symbol, extra bits for distance */

    int len;            /* length for copy */

    int dist;           /* distance for copy */

    int copy;           /* copy counter */

    unsigned char *from, *to;   /* copy pointers */

    static int virgin = 1;                              /* build tables once */

    static short litcnt[MAXBITS+1], litsym[256];        /* litcode memory */

    static short lencnt[MAXBITS+1], lensym[16];         /* lencode memory */

    static short distcnt[MAXBITS+1], distsym[64];       /* distcode memory */

    static struct huffman litcode = {litcnt, litsym};   /* length code */

    static struct huffman lencode = {lencnt, lensym};   /* length code */

    static struct huffman distcode = {distcnt, distsym};/* distance code */

        /* bit lengths of literal codes */

    static const unsigned char litlen[] = {

        11, 124, 8, 7, 28, 7, 188, 13, 76, 4, 10, 8, 12, 10, 12, 10, 8, 23, 8,

        9, 7, 6, 7, 8, 7, 6, 55, 8, 23, 24, 12, 11, 7, 9, 11, 12, 6, 7, 22, 5,

        7, 24, 6, 11, 9, 6, 7, 22, 7, 11, 38, 7, 9, 8, 25, 11, 8, 11, 9, 12,

        8, 12, 5, 38, 5, 38, 5, 11, 7, 5, 6, 21, 6, 10, 53, 8, 7, 24, 10, 27,

        44, 253, 253, 253, 252, 252, 252, 13, 12, 45, 12, 45, 12, 61, 12, 45,

        44, 173};

        /* bit lengths of length codes 0..15 */

    static const unsigned char lenlen[] = {2, 35, 36, 53, 38, 23};

        /* bit lengths of distance codes 0..63 */

    static const unsigned char distlen[] = {2, 20, 53, 230, 247, 151, 248};

    static const short base[16] = {     /* base for length codes */

        3, 2, 4, 5, 6, 7, 8, 9, 10, 12, 16, 24, 40, 72, 136, 264};

    static const char extra[16] = {     /* extra bits for length codes */

        0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8};

    /* set up decoding tables (once--might not be thread-safe) */

    if (virgin) {

        construct(&litcode, litlen, sizeof(litlen));

        construct(&lencode, lenlen, sizeof(lenlen));

        construct(&distcode, distlen, sizeof(distlen));

        virgin = 0;

    }

    /* read header */

    lit = bits(s, 8);

    if (lit > 1) return -1;

    dict = bits(s, 8);

    if (dict < 4 || dict > 6) return -2;

    /* decode literals and length/distance pairs */

    do {

        if (bits(s, 1)) {

            /* get length */

            symbol = decode(s, &lencode);

            len = base[symbol] + bits(s, extra[symbol]);

            if (len == 519) break;              /* end code */

            /* get distance */

            symbol = len == 2 ? 2 : dict;

            dist = decode(s, &distcode) << symbol;

            dist += bits(s, symbol);

            dist++;

            if (s->first && dist > s->next)

                return -3;              /* distance too far back */

            /* copy length bytes from distance bytes back */

            do {

                to = s->out + s->next;

                from = to - dist;

                copy = MAXWIN;

                if (s->next < dist) {

                    from += copy;

                    copy = dist;

                }

                copy -= s->next;

                if (copy > len) copy = len;

                len -= copy;

                s->next += copy;

                do {

                    *to++ = *from++;

                } while (--copy);

                if (s->next == MAXWIN) {

                    if (s->outfun(s->outhow, s->out, s->next)) return 1;

                    s->next = 0;

                    s->first = 0;

                }

            } while (len != 0);

        }

        else {

            /* get literal and write it */

            symbol = lit ? decode(s, &litcode) : bits(s, 8);

            s->out[s->next++] = symbol;

            if (s->next == MAXWIN) {

                if (s->outfun(s->outhow, s->out, s->next)) return 1;

                s->next = 0;

                s->first = 0;

            }

        }

    } while (1);

    return 0;

}

/* See comments in blast.h */

int blast(blast_in infun, void *inhow, blast_out outfun, void *outhow)

{

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

    int err;                    /* return value */

    /* initialize input state */

    s.infun = infun;

    s.inhow = inhow;

    s.left = 0;

    s.bitbuf = 0;

    s.bitcnt = 0;

    /* initialize output state */

    s.outfun = outfun;

    s.outhow = outhow;

    s.next = 0;

    s.first = 1;

    /* 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 decomp(), return error */

    else

        err = decomp(&s);               /* decompress */

    /* write any leftover output and update the error code if needed */

    if (err != 1 && s.next && s.outfun(s.outhow, s.out, s.next) && err == 0)

        err = 1;

    return err;

}

#ifdef TEST

/* Example of how to use blast() */

#include <stdio.h>

#include <stdlib.h>

#define CHUNK 16384

local unsigned inf(void *how, unsigned char **buf)

{

    static unsigned char hold[CHUNK];

    *buf = hold;

    return fread(hold, 1, CHUNK, (FILE *)how);

}

local int outf(void *how, unsigned char *buf, unsigned len)

{

    return fwrite(buf, 1, len, (FILE *)how) != len;

}

/* Decompress a PKWare Compression Library stream from stdin to stdout */

int main(void)

{

    int ret, n;

    /* decompress to stdout */

    ret = blast(inf, stdin, outf, stdout);

    if (ret != 0) fprintf(stderr, "blast error: %d\n", ret);

    /* see if there are any leftover bytes */

    n = 0;

    while (getchar() != EOF) n++;

    if (n) fprintf(stderr, "blast warning: %d unused bytes of input\n", n);

    /* return blast() error code */

    return ret;

}

#endif