rle.c

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/*
 * RLE encoder
 * Copyright (c) 2007 Bobby Bingham
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * 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
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
 
#include <string.h>
 
#include "libavutil/common.h"
 
#include "rle.h"
 
int ff_rle_count_pixels(const uint8_t *start, int len, int bpp, int same)
{
    const uint8_t *pos;
    int count = 1;
 
    for (pos = start + bpp; count < FFMIN(127, len); pos += bpp, count++) {
        if (same != !memcmp(pos - bpp, pos, bpp)) {
            if (!same) {
                /* if bpp == 1, then 0 1 1 0 is more efficiently encoded as a
                 * single raw block of pixels. For larger bpp, RLE is as good
                 * or better */
                if (bpp == 1 && count + 1 < FFMIN(127, len) && *pos != *(pos + 1))
                    continue;
 
                /* if RLE can encode the next block better than as a raw block,
                 * back up and leave _all_ the identical pixels for RLE */
                count--;
            }
            break;
        }
    }
 
    return count;
}
 
int ff_rle_encode(uint8_t *outbuf, int out_size, const uint8_t *ptr, int bpp,
                  int w, int add_rep, int xor_rep, int add_raw, int xor_raw)
{
    int count, x;
    uint8_t *out = outbuf;
 
    for (x = 0; x < w; x += count) {
        /* see if we can encode the next set of pixels with RLE */
        if ((count = ff_rle_count_pixels(ptr, w - x, bpp, 1)) > 1) {
            if (out + bpp + 1 > outbuf + out_size)
                return -1;
 
            *out++ = (count ^ xor_rep) + add_rep;
            memcpy(out, ptr, bpp);
            out += bpp;
        } else {
            /* fall back on uncompressed */
            count = ff_rle_count_pixels(ptr, w - x, bpp, 0);
            if (out + bpp * count >= outbuf + out_size)
                return -1;
 
            *out++ = (count ^ xor_raw) + add_raw;
            memcpy(out, ptr, bpp * count);
            out += bpp * count;
        }
 
        ptr += count * bpp;
    }
 
    return out - outbuf;
}