/*-
 * Copyright (c) 2002-2004 Jan Dubiec <jdx@slackware.pl>
 * Copyright (c) 2007 Alexander Motin <mav@freebsd.org>
 * 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 decompression library.
 * Version 1.0
 *
 * Note that Hi/Fn (later acquired by Exar Corporation) held US patents
 * on some implementation-critical aspects of MPPC compression.
 * These patents lapsed due to non-payment of fees in 2007 and by 2015
 * expired altogether.
 */

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

#include <net/mppc.h>

#define MPPE_HIST_LEN          8192

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

static uint32_t __inline
getbits(const uint8_t *buf, const uint32_t n, uint32_t *i, uint32_t *l)
{
    static const uint32_t m[] = {0x00, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff};
    uint32_t res, ol;

    ol = *l;
    if (*l >= n) {
        *l = (*l) - n;
        res = (buf[*i] & m[ol]) >> (*l);
        if (*l == 0) {
            *l = 8;
            (*i)++;
        }
    } else {
        *l = 8 - n + (*l);
        res = (buf[(*i)++] & m[ol]) << 8;
        res = (res | buf[*i]) >> (*l);
    }

    return (res);
}

static uint32_t __inline
getbyte(const uint8_t *buf, const uint32_t i, const uint32_t l)
{
    if (l == 8) {
        return (buf[i]);
    } else {
        return ((((buf[i] << 8) | buf[i+1]) >> l) & 0xff);
    }
}

static void __inline
lamecopy(uint8_t *dst, uint8_t *src, uint32_t len)
{
    while (len--)
        *dst++ = *src++;
}

size_t MPPC_SizeOfDecompressionHistory(void)
{
    return (sizeof(struct MPPC_decomp_state));
}

void MPPC_InitDecompressionHistory(char *history)
{
    struct MPPC_decomp_state      *state = (struct MPPC_decomp_state*)history;

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

int MPPC_Decompress(u_char **src, u_char **dst, u_long *srcCnt, u_long *dstCnt, char *history, int flags)
{
    struct MPPC_decomp_state      *state = (struct MPPC_decomp_state*)history;
    uint32_t olen, off, len, bits, val, sig, i, l;
    uint8_t *hist, *s;
    u_char *isrc = *src;
    int rtn = MPPC_OK;

    if ((flags & MPPC_RESTART_HISTORY) != 0) {
        memcpy(state->hist, state->hist + MPPE_HIST_LEN, MPPE_HIST_LEN);
        state->histptr = MPPE_HIST_LEN;
    }

    hist = state->hist + state->histptr;
    olen = len = i = 0;
    l = 8;
    bits = *srcCnt * 8;
    while (bits >= 8) {
        val = getbyte(isrc, i++, l);
        if (val < 0x80) {               /* literal byte < 0x80 */
            if (state->histptr < 2*MPPE_HIST_LEN) {
                /* Copy uncompressed byte to the history. */
                (state->hist)[(state->histptr)++] = (uint8_t) val;
            } else {
                /* Buffer overflow; drop packet. */
                rtn &= ~MPPC_OK;
                return rtn;
            }
            olen++;
            bits -= 8;
            continue;
        }

        sig = val & 0xc0;
        if (sig == 0x80) {              /* literal byte >= 0x80 */
            if (state->histptr < 2*MPPE_HIST_LEN) {
                /* Copy uncompressed byte to the history. */
                (state->hist)[(state->histptr)++] = 
                    (uint8_t) (0x80|((val&0x3f)<<1)|getbits(isrc, 1 , &i ,&l));
            } else {
                /* buffer overflow; drop packet */
                rtn &= ~MPPC_OK;
                return (rtn);
            }
            olen++;
            bits -= 9;
            continue;
        }

        /* Not a literal byte so it must be an (offset,length) pair */
        /* decode offset */
        sig = val & 0xf0;
        if (sig == 0xf0) {              /* 10-bit offset; 0 <= offset < 64 */
            off = (((val&0x0f)<<2)|getbits(isrc, 2 , &i ,&l));
            bits -= 10;
        } else {
            if (sig == 0xe0) {          /* 12-bit offset; 64 <= offset < 320 */
                off = ((((val&0x0f)<<4)|getbits(isrc, 4 , &i ,&l))+64);
                bits -= 12;
            } else {
                if ((sig&0xe0) == 0xc0) {/* 16-bit offset; 320 <= offset < 8192 */
                    off = ((((val&0x1f)<<8)|getbyte(isrc, i++, l))+320);
                    bits -= 16;
                    if (off > MPPE_HIST_LEN - 1) {
                        rtn &= ~MPPC_OK;
                        return (rtn);
                    }
                } else {                /* This shouldn't happen. */
                    rtn &= ~MPPC_OK;
                    return (rtn);
                }
            }
        }
        /* Decode length of match. */
        val = getbyte(isrc, i, l);
        if ((val & 0x80) == 0x00) {                     /* len = 3 */
            len = 3;
            bits--;
            getbits(isrc, 1 , &i ,&l);
        } else if ((val & 0xc0) == 0x80) {              /* 4 <= len < 8 */
            len = 0x04 | ((val>>4) & 0x03);
            bits -= 4;
            getbits(isrc, 4 , &i ,&l);
        } else if ((val & 0xe0) == 0xc0) {              /* 8 <= len < 16 */
            len = 0x08 | ((val>>2) & 0x07);
            bits -= 6;
            getbits(isrc, 6 , &i ,&l);
        } else if ((val & 0xf0) == 0xe0) {              /* 16 <= len < 32 */
            len = 0x10 | (val & 0x0f);
            bits -= 8;
            i++;
        } else {
            bits -= 8;
            val = (val << 8) | getbyte(isrc, ++i, l);
            if ((val & 0xf800) == 0xf000) {             /* 32 <= len < 64 */
                len = 0x0020 | ((val >> 6) & 0x001f);
                bits -= 2;
                getbits(isrc, 2 , &i ,&l);
            } else if ((val & 0xfc00) == 0xf800) {      /* 64 <= len < 128 */
                len = 0x0040 | ((val >> 4) & 0x003f);
                bits -= 4;
                getbits(isrc, 4 , &i ,&l);
            } else if ((val & 0xfe00) == 0xfc00) {      /* 128 <= len < 256 */
                len = 0x0080 | ((val >> 2) & 0x007f);
                bits -= 6;
                getbits(isrc, 6 , &i ,&l);
            } else if ((val & 0xff00) == 0xfe00) {      /* 256 <= len < 512 */
                len = 0x0100 | (val & 0x00ff);
                bits -= 8;
                i++;
            } else {
                bits -= 8;
                val = (val << 8) | getbyte(isrc, ++i, l);
                if ((val & 0xff8000) == 0xff0000) {     /* 512 <= len < 1024 */
                    len = 0x000200 | ((val >> 6) & 0x0001ff);
                    bits -= 2;
                    getbits(isrc, 2 , &i ,&l);
                } else if ((val & 0xffc000) == 0xff8000) {/* 1024 <= len < 2048 */
                    len = 0x000400 | ((val >> 4) & 0x0003ff);
                    bits -= 4;
                    getbits(isrc, 4 , &i ,&l);
                } else if ((val & 0xffe000) == 0xffc000) {/* 2048 <= len < 4096 */
                    len = 0x000800 | ((val >> 2) & 0x0007ff);
                    bits -= 6;
                    getbits(isrc, 6 , &i ,&l);
                } else if ((val & 0xfff000) == 0xffe000) {/* 4096 <= len < 8192 */
                    len = 0x001000 | (val & 0x000fff);
                    bits -= 8;
                    i++;
                } else {                                /* NOTREACHED */
                    rtn &= ~MPPC_OK;
                    return (rtn);
                }
            }
        }

        s = state->hist + state->histptr;
        state->histptr += len;
        olen += len;
        if (state->histptr < 2*MPPE_HIST_LEN) {
            /* Copy uncompressed bytes to the history. */

            /*
             * In some cases len may be greater than off. It means that memory
             * areas pointed by s and s-off overlap. To decode that strange case
             * data should be copied exactly by address increasing to make
             * some data repeated.
             */
            lamecopy(s, s - off, len);
        } else {
            /* Buffer overflow; drop packet. */
            rtn &= ~MPPC_OK;
            return (rtn);
        }
    }

    /* Do PFC decompression. */
    len = olen;
    if ((hist[0] & 0x01) != 0) {
        (*dst)[0] = 0;
        (*dst)++;
        len++;
    }

    if (len <= *dstCnt) {
        /* Copy uncompressed packet to the output buffer. */
        memcpy(*dst, hist, olen);
    } else {
        /* Buffer overflow; drop packet. */
        rtn |= MPPC_DEST_EXHAUSTED;
    }

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

    return (rtn);
}