mppcc.c

MPPC compress/decompress algorithm

/*-
 * Copyright (c) 2002-2004 Jan Dubiec <[e-mail]>
 * Copyright (c) 2007 Alexander Motin <[e-mail]>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice unmodified, this list of conditions, and the following
 *    disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * MPPC compression library.
 * Version 1.0
 *
 * Please note that Hi/Fn (http://www.hifn.com) holds US patents on some 
 * implementation critical aspects of MPPC so you should check if those 
 * patents are valid in your country in order to avoid legal problems.
 */

#include <sys/param.h>
#include <sys/systm.h>

#include <net/mppc.h>

#define MPPE_HIST_LEN          8192

#define HASH(x)		(((40543*(((((x)[0]<<4)^(x)[1])<<4)^(x)[2]))>>4) & 0x1fff)

struct MPPC_comp_state {
    uint8_t	hist[2*MPPE_HIST_LEN];
    uint16_t	histptr;
    uint16_t	hash[MPPE_HIST_LEN];
};

/* inserts 1 to 8 bits into the output buffer */
static void __inline 
putbits8(uint8_t *buf, uint32_t val, const uint32_t n, uint32_t *i, uint32_t *l)
{
    buf += *i;
    if (*l >= n) {
	*l = (*l) - n;
	val <<= *l;
	*buf = *buf | (val & 0xff);
	if (*l == 0) {
	    *l = 8;
	    (*i)++;
	    *(++buf) = 0;
	}
    } else {
	(*i)++;
	*l = 8 - n + (*l);
	val <<= *l;
	*buf = *buf | ((val >> 8) & 0xff);
	*(++buf) = val & 0xff;
    }
}

/* inserts 9 to 16 bits into the output buffer */
static void __inline 
putbits16(uint8_t *buf, uint32_t val, const uint32_t n, uint32_t *i, uint32_t *l)
{
    buf += *i;
    if (*l >= n - 8) {
	(*i)++;
	*l = 8 - n + (*l);
	val <<= *l;
	*buf = *buf | ((val >> 8) & 0xff);
	*(++buf) = val & 0xff;
	if (*l == 0) {
	    *l = 8;
	    (*i)++;
	    *(++buf) = 0;
	}
    } else {
	(*i)++; (*i)++;
	*l = 16 - n + (*l);
	val <<= *l;
	*buf = *buf | ((val >> 16) & 0xff);
	*(++buf) = (val >> 8) & 0xff;
	*(++buf) = val & 0xff;
    }
}

/* inserts 17 to 24 bits into the output buffer */
static void __inline 
putbits24(uint8_t *buf, uint32_t val, const uint32_t n, uint32_t *i, uint32_t *l)
{
    buf += *i;
    if (*l >= n - 16) {
	(*i)++; (*i)++;
	*l = 16 - n + (*l);
	val <<= *l;
	*buf = *buf | ((val >> 16) & 0xff);
	*(++buf) = (val >> 8) & 0xff;
	*(++buf) = val & 0xff;
	if (*l == 0) {
	    *l = 8;
	    (*i)++;
	    *(++buf) = 0;
	}
    } else {
	(*i)++; (*i)++; (*i)++;
	*l = 24 - n + (*l);
	val <<= *l;
	*buf = *buf | ((val >> 24) & 0xff);
	*(++buf) = (val >> 16) & 0xff;
	*(++buf) = (val >> 8) & 0xff;
	*(++buf) = val & 0xff;
    }
}

size_t MPPC_SizeOfCompressionHistory(void)
{
    return sizeof(struct MPPC_comp_state);
}

void MPPC_InitCompressionHistory(char *history)
{
    struct MPPC_comp_state      *state = (struct MPPC_comp_state*)history;

    bzero(history, sizeof(struct MPPC_comp_state));
    state->histptr = MPPE_HIST_LEN;
}

int MPPC_Compress(u_char **src, u_char **dst, u_long *srcCnt, u_long *dstCnt, char *history, int flags, int undef)
{
    struct MPPC_comp_state	*state = (struct MPPC_comp_state*)history;
    uint32_t olen, off, len, idx, i, l;
    uint8_t *hist, *sbuf, *p, *q, *r, *s;    
    int	rtn = MPPC_OK;

    /*  
	At this point, to avoid possible buffer overflow caused by packet
	expansion during/after compression, we should make sure we have
	space for the worst case.

	Maximum MPPC packet expansion is 12.5%. This is the worst case when
	all octets in the input buffer are >= 0x80 and we cannot find any
	repeated tokens.
    */
    if (*dstCnt < (*srcCnt * 9 / 8 + 2)) {
	rtn &= ~MPPC_OK;
	return rtn;
    }

    /* We can't compress more then MPPE_HIST_LEN bytes in a call */
    if (*srcCnt > MPPE_HIST_LEN) {
	rtn &= ~MPPC_OK;
	return rtn;
    }

    hist = state->hist + MPPE_HIST_LEN;
    /* check if there is enough room at the end of the history */
    if (state->histptr + *srcCnt >= 2*MPPE_HIST_LEN) {
	rtn |= MPPC_RESTART_HISTORY;
	state->histptr = MPPE_HIST_LEN;
	memcpy(state->hist, hist, MPPE_HIST_LEN);
    }
    /* add packet to the history */
    sbuf = state->hist + state->histptr;
    memcpy(sbuf, *src, *srcCnt);
    state->histptr += *srcCnt;

    /* compress data */
    r = sbuf + *srcCnt;
    **dst = olen = i = 0;
    l = 8;
    while (i < *srcCnt - 2) {
	s = q = sbuf + i;

	/* Prognose matching position using hash function */
	idx = HASH(s);
	p = hist + state->hash[idx];
	state->hash[idx] = (uint16_t) (s - hist);
	if (p > s)	/* It was before MPPC_RESTART_HISTORY */
	    p -= MPPE_HIST_LEN;	/* try previous history buffer */
	off = s - p;

	/* Check our prognosis */
	if (off > MPPE_HIST_LEN - 1 || off < 1 || *p++ != *s++ || *p++ != *s++ ||
	    *p++ != *s++) {
	    /* no match found; encode literal byte */
	    if ((*src)[i] < 0x80) {		/* literal byte < 0x80 */
		putbits8(*dst, (uint32_t) (*src)[i], 8, &olen, &l);
	    } else {				/* literal byte >= 0x80 */
		putbits16(*dst, (uint32_t) (0x100|((*src)[i]&0x7f)), 9, &olen, &l);
	    }
	    ++i;
	    continue;
	}

	/* Find length of the matching fragment */
#if defined(__amd64__) || defined(__i386__)
	/* Optimization for CPUs without strict data aligning requirements */
	while ((*((uint32_t*)p) == *((uint32_t*)s)) && (s < (r - 3))) {
	    p+=4;
	    s+=4;
	}
#endif
	while((*p++ == *s++) && (s <= r));
	len = s - q - 1;
	i += len;

	/* at least 3 character match found; code data */
	/* encode offset */
	if (off < 64) {			/* 10-bit offset; 0 <= offset < 64 */
	    putbits16(*dst, 0x3c0|off, 10, &olen, &l);
	} else if (off < 320) {		/* 12-bit offset; 64 <= offset < 320 */
	    putbits16(*dst, 0xe00|(off-64), 12, &olen, &l);
	} else if (off < 8192) {	/* 16-bit offset; 320 <= offset < 8192 */
	    putbits16(*dst, 0xc000|(off-320), 16, &olen, &l);
	} else {
	    /* This shouldn't happen. */
	    rtn &= ~MPPC_OK;
	    return rtn;
	}

	/* encode length of match */
	if (len < 4) {			/* length = 3 */
	    putbits8(*dst, 0, 1, &olen, &l);
	} else if (len < 8) {		/* 4 <= length < 8 */
	    putbits8(*dst, 0x08|(len&0x03), 4, &olen, &l);
	} else if (len < 16) {		/* 8 <= length < 16 */
	    putbits8(*dst, 0x30|(len&0x07), 6, &olen, &l);
	} else if (len < 32) {		/* 16 <= length < 32 */
	    putbits8(*dst, 0xe0|(len&0x0f), 8, &olen, &l);
	} else if (len < 64) {		/* 32 <= length < 64 */
	    putbits16(*dst, 0x3c0|(len&0x1f), 10, &olen, &l);
	} else if (len < 128) {		/* 64 <= length < 128 */
	    putbits16(*dst, 0xf80|(len&0x3f), 12, &olen, &l);
	} else if (len < 256) {		/* 128 <= length < 256 */
	    putbits16(*dst, 0x3f00|(len&0x7f), 14, &olen, &l);
	} else if (len < 512) {		/* 256 <= length < 512 */
	    putbits16(*dst, 0xfe00|(len&0xff), 16, &olen, &l);
	} else if (len < 1024) {	/* 512 <= length < 1024 */
	    putbits24(*dst, 0x3fc00|(len&0x1ff), 18, &olen, &l);
	} else if (len < 2048) {	/* 1024 <= length < 2048 */
	    putbits24(*dst, 0xff800|(len&0x3ff), 20, &olen, &l);
	} else if (len < 4096) {	/* 2048 <= length < 4096 */
	    putbits24(*dst, 0x3ff000|(len&0x7ff), 22, &olen, &l);
	} else if (len < 8192) {	/* 4096 <= length < 8192 */
	    putbits24(*dst, 0xffe000|(len&0xfff), 24, &olen, &l);
	} else {
	    /* This shouldn't happen. */
	    rtn &= ~MPPC_OK;
	    return rtn;
	}
    }

    /* Add remaining octets to the output */
    while(*srcCnt - i > 0) {
	if ((*src)[i] < 0x80) {	/* literal byte < 0x80 */
	    putbits8(*dst, (uint32_t) (*src)[i++], 8, &olen, &l);
	} else {		/* literal byte >= 0x80 */
	    putbits16(*dst, (uint32_t) (0x100|((*src)[i++]&0x7f)), 9, &olen, &l);
	}
    }

    /* Reset unused bits of the last output octet */
    if ((l != 0) && (l != 8)) {
	putbits8(*dst, 0, l, &olen, &l);
    }

    /* If result is bigger then original, set flag and flush history */
    if ((*srcCnt < olen) || ((flags & MPPC_SAVE_HISTORY) == 0)) {
	if (*srcCnt < olen)
	    rtn |= MPPC_EXPANDED;
	bzero(history, sizeof(struct MPPC_comp_state));
	state->histptr = MPPE_HIST_LEN;
    }

    *src += *srcCnt;
    *srcCnt = 0;
    *dst += olen;
    *dstCnt -= olen;

    return rtn;
}