lzo.c 5.34 KB
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/*
 * LZO 1x decompression
 * Copyright (c) 2006 Reimar Doeffinger
 *
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 * This file is part of Libav.
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 *
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 * Libav is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * Libav is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
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 * License along with Libav; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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#include <string.h>

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#include "avutil.h"
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#include "common.h"
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#include "intreadwrite.h"
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#include "lzo.h"

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/// Define if we may write up to 12 bytes beyond the output buffer.
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#define OUTBUF_PADDED 1
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/// Define if we may read up to 8 bytes beyond the input buffer.
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#define INBUF_PADDED 1
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typedef struct LZOContext {
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    const uint8_t *in, *in_end;
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    uint8_t *out_start, *out, *out_end;
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    int error;
} LZOContext;

/**
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 * @brief Reads one byte from the input buffer, avoiding an overrun.
 * @return byte read
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 */
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static inline int get_byte(LZOContext *c)
{
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    if (c->in < c->in_end)
        return *c->in++;
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    c->error |= AV_LZO_INPUT_DEPLETED;
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    return 1;
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}

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#ifdef INBUF_PADDED
#define GETB(c) (*(c).in++)
#else
#define GETB(c) get_byte(&(c))
#endif

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/**
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 * @brief Decodes a length value in the coding used by lzo.
 * @param x previous byte value
 * @param mask bits used from x
 * @return decoded length value
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 */
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static inline int get_len(LZOContext *c, int x, int mask)
{
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    int cnt = x & mask;
    if (!cnt) {
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        while (!(x = get_byte(c)))
            cnt += 255;
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        cnt += mask + x;
    }
    return cnt;
}

/**
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 * @brief Copies bytes from input to output buffer with checking.
 * @param cnt number of bytes to copy, must be >= 0
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 */
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static inline void copy(LZOContext *c, int cnt)
{
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    register const uint8_t *src = c->in;
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    register uint8_t *dst       = c->out;
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    if (cnt > c->in_end - src) {
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        cnt       = FFMAX(c->in_end - src, 0);
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        c->error |= AV_LZO_INPUT_DEPLETED;
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    }
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    if (cnt > c->out_end - dst) {
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        cnt       = FFMAX(c->out_end - dst, 0);
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        c->error |= AV_LZO_OUTPUT_FULL;
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    }
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#if defined(INBUF_PADDED) && defined(OUTBUF_PADDED)
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    AV_COPY32U(dst, src);
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    src += 4;
    dst += 4;
    cnt -= 4;
    if (cnt > 0)
#endif
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    memcpy(dst, src, cnt);
    c->in  = src + cnt;
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    c->out = dst + cnt;
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}

/**
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 * @brief Copies previously decoded bytes to current position.
 * @param back how many bytes back we start
 * @param cnt number of bytes to copy, must be >= 0
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 *
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 * cnt > back is valid, this will copy the bytes we just copied,
 * thus creating a repeating pattern with a period length of back.
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 */
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static inline void copy_backptr(LZOContext *c, int back, int cnt)
{
    register uint8_t *dst       = c->out;
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    if (dst - c->out_start < back) {
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        c->error |= AV_LZO_INVALID_BACKPTR;
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        return;
    }
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    if (cnt > c->out_end - dst) {
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        cnt       = FFMAX(c->out_end - dst, 0);
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        c->error |= AV_LZO_OUTPUT_FULL;
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    }
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    av_memcpy_backptr(dst, back, cnt);
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    c->out = dst + cnt;
}

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int av_lzo1x_decode(void *out, int *outlen, const void *in, int *inlen)
{
    int state = 0;
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    int x;
    LZOContext c;
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    if (!*outlen || !*inlen) {
        int res = 0;
        if (!*outlen)
            res |= AV_LZO_OUTPUT_FULL;
        if (!*inlen)
            res |= AV_LZO_INPUT_DEPLETED;
        return res;
    }
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    c.in      = in;
    c.in_end  = (const uint8_t *)in + *inlen;
    c.out     = c.out_start = out;
    c.out_end = (uint8_t *)out + *outlen;
    c.error   = 0;
    x         = GETB(c);
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    if (x > 17) {
        copy(&c, x - 17);
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        x = GETB(c);
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        if (x < 16)
            c.error |= AV_LZO_ERROR;
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    }
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    if (c.in > c.in_end)
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        c.error |= AV_LZO_INPUT_DEPLETED;
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    while (!c.error) {
        int cnt, back;
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        if (x > 15) {
            if (x > 63) {
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                cnt  = (x >> 5) - 1;
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                back = (GETB(c) << 3) + ((x >> 2) & 7) + 1;
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            } else if (x > 31) {
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                cnt  = get_len(&c, x, 31);
                x    = GETB(c);
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                back = (GETB(c) << 6) + (x >> 2) + 1;
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            } else {
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                cnt   = get_len(&c, x, 7);
                back  = (1 << 14) + ((x & 8) << 11);
                x     = GETB(c);
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                back += (GETB(c) << 6) + (x >> 2);
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                if (back == (1 << 14)) {
                    if (cnt != 1)
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                        c.error |= AV_LZO_ERROR;
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                    break;
                }
            }
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        } else if (!state) {
            cnt = get_len(&c, x, 15);
            copy(&c, cnt + 3);
            x = GETB(c);
            if (x > 15)
                continue;
            cnt  = 1;
            back = (1 << 11) + (GETB(c) << 2) + (x >> 2) + 1;
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        } else {
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            cnt  = 0;
            back = (GETB(c) << 2) + (x >> 2) + 1;
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        }
        copy_backptr(&c, back, cnt + 2);
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        state =
        cnt   = x & 3;
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        copy(&c, cnt);
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        x = GETB(c);
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    }
    *inlen = c.in_end - c.in;
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    if (c.in > c.in_end)
        *inlen = 0;
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    *outlen = c.out_end - c.out;
    return c.error;
}