decompressor.c

使用visual studio 2005 开发的开源文件、磁盘加密软件。这是6.1a版。加密自己资料的好工具。也是学习的优秀范本。结成了众多加密算法。

/*
  puff.c
  Copyright (C) 2002-2004 Mark Adler, all rights reserved
  version 1.8, 9 Jan 2004

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the author be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.

  Mark Adler    [e-mail]
*/

/* Adapted by TrueCrypt Foundation */


#define local static            /* for local function definitions */
#define NIL ((unsigned char *)0)        /* for no output option */

/*
 * 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 int outlen;       /* available space at out */
    unsigned int outcnt;       /* bytes written to out so far */

    /* input state */
    unsigned char *in;          /* input buffer */
    unsigned int incnt;        /* bytes read so far */
    int bitbuf;                 /* bit buffer */
    int bitcnt;                 /* number of bits in bit buffer */
};


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) {
        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));
}


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 */
    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->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;
}


struct huffman {
    short *count;       /* number of symbols of each length */
    short *symbol;      /* canonically ordered symbols */
};


#ifdef SLOW
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 */

    code = first = index = 0;
    for (len = 1; len <= MAXBITS; len++) {
        code |= bits(s, 1);             /* get next bit */
        count = h->count[len];
        if (code < first + count)       /* 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 -9;                          /* 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, 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 < 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;
        bitbuf = s->in[s->incnt++];
        if (left > 8) left = 8;
    }
    return -9;                          /* ran out of codes */
}
#endif /* SLOW */


local int construct(struct huffman *h, 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;