utils.c

        val += num / den;
        num = num % den;
    }
    f->val = val;
    f->num = num;
    f->den = den;
}

/**
 * Set f to (val + 0.5).
 */
void av_frac_set(AVFrac *f, int64_t val)
{
    f->val = val;
    f->num = f->den >> 1;
}

/**
 * Fractionnal addition to f: f = f + (incr / f->den).
 *
 * @param f fractional number
 * @param incr increment, can be positive or negative
 */
void av_frac_add(AVFrac *f, int64_t incr)
{
    int64_t num, den;

    num = f->num + incr;
    den = f->den;
    if (num < 0) {
        f->val += num / den;
        num = num % den;
        if (num < 0) {
            num += den;
            f->val--;
        }
    } else if (num >= den) {
        f->val += num / den;
        num = num % den;
    }
    f->num = num;
}

/**
 * register a new image format
 * @param img_fmt Image format descriptor
 */
void av_register_image_format(AVImageFormat *img_fmt)
{
    AVImageFormat **p;

    p = &first_image_format;
    while (*p != NULL) p = &(*p)->next;
    *p = img_fmt;
    img_fmt->next = NULL;
}

/**
 * Guesses image format based on data in the image.
 */
AVImageFormat *av_probe_image_format(AVProbeData *pd)
{
    AVImageFormat *fmt1, *fmt;
    int score, score_max;

    fmt = NULL;
    score_max = 0;
    for(fmt1 = first_image_format; fmt1 != NULL; fmt1 = fmt1->next) {
        if (fmt1->img_probe) {
            score = fmt1->img_probe(pd);
            if (score > score_max) {
                score_max = score;
                fmt = fmt1;
            }
        }
    }
    return fmt;
}

/**
 * Guesses image format based on file name extensions.
 */
AVImageFormat *guess_image_format(const char *filename)
{
    AVImageFormat *fmt1;

    for(fmt1 = first_image_format; fmt1 != NULL; fmt1 = fmt1->next) {
        if (fmt1->extensions && match_ext(filename, fmt1->extensions))
            return fmt1;
    }
    return NULL;
}

/**
 * Read an image from a stream. 
 * @param gb byte stream containing the image
 * @param fmt image format, NULL if probing is required
 */
int av_read_image(ByteIOContext *pb, const char *filename,
                  AVImageFormat *fmt,
                  int (*alloc_cb)(void *, AVImageInfo *info), void *opaque)
{
    char buf[PROBE_BUF_SIZE];
    AVProbeData probe_data, *pd = &probe_data;
    offset_t pos;
    int ret;

    if (!fmt) {
        pd->filename = filename;
        pd->buf = buf;
        pos = url_ftell(pb);
        pd->buf_size = get_buffer(pb, buf, PROBE_BUF_SIZE);
        url_fseek(pb, pos, SEEK_SET);
        fmt = av_probe_image_format(pd);
    }
    if (!fmt)
        return AVERROR_NOFMT;
    ret = fmt->img_read(pb, alloc_cb, opaque);
    return ret;
}

/**
 * Write an image to a stream.
 * @param pb byte stream for the image output
 * @param fmt image format
 * @param img image data and informations
 */
int av_write_image(ByteIOContext *pb, AVImageFormat *fmt, AVImageInfo *img)
{
    return fmt->img_write(pb, img);
}