int ff_scale_eval_dimensions(void *log_ctx,

    const char *w_expr, const char *h_expr,

    AVFilterLink *inlink, AVFilterLink *outlink,

    int *ret_w, int *ret_h)

{

    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);

    const AVPixFmtDescriptor *out_desc = av_pix_fmt_desc_get(outlink->format);

    const char *expr;

    int w, h;

    int factor_w, factor_h;

    int eval_w, eval_h;

    int ret;

    double var_values[VARS_NB], res;



    var_values[VAR_PI]    = M_PI;

    var_values[VAR_PHI]   = M_PHI;

    var_values[VAR_E]     = M_E;

    var_values[VAR_IN_W]  = var_values[VAR_IW] = inlink->w;

    var_values[VAR_IN_H]  = var_values[VAR_IH] = inlink->h;

    var_values[VAR_OUT_W] = var_values[VAR_OW] = NAN;

    var_values[VAR_OUT_H] = var_values[VAR_OH] = NAN;

    var_values[VAR_A]     = (double) inlink->w / inlink->h;

    var_values[VAR_SAR]   = inlink->sample_aspect_ratio.num ?

        (double) inlink->sample_aspect_ratio.num / inlink->sample_aspect_ratio.den : 1;

    var_values[VAR_DAR]   = var_values[VAR_A] * var_values[VAR_SAR];

    var_values[VAR_HSUB]  = 1 << desc->log2_chroma_w;

    var_values[VAR_VSUB]  = 1 << desc->log2_chroma_h;

    var_values[VAR_OHSUB] = 1 << out_desc->log2_chroma_w;

    var_values[VAR_OVSUB] = 1 << out_desc->log2_chroma_h;



    /* evaluate width and height */

    av_expr_parse_and_eval(&res, (expr = w_expr),

                           var_names, var_values,

                           NULL, NULL, NULL, NULL, NULL, 0, log_ctx);

    eval_w = var_values[VAR_OUT_W] = var_values[VAR_OW] = res;



    if ((ret = av_expr_parse_and_eval(&res, (expr = h_expr),

                                      var_names, var_values,

                                      NULL, NULL, NULL, NULL, NULL, 0, log_ctx)) < 0)

        goto fail;

    eval_h = var_values[VAR_OUT_H] = var_values[VAR_OH] = res;

    /* evaluate again the width, as it may depend on the output height */

    if ((ret = av_expr_parse_and_eval(&res, (expr = w_expr),

                                      var_names, var_values,

                                      NULL, NULL, NULL, NULL, NULL, 0, log_ctx)) < 0)

        goto fail;

    eval_w = res;



    w = eval_w;

    h = eval_h;



    /* Check if it is requested that the result has to be divisible by a some

     * factor (w or h = -n with n being the factor). */

    factor_w = 1;

    factor_h = 1;

    if (w < -1) {

        factor_w = -w;

    }

    if (h < -1) {

        factor_h = -h;

    }



    if (w < 0 && h < 0)

        eval_w = eval_h = 0;



    if (!(w = eval_w))

        w = inlink->w;

    if (!(h = eval_h))

        h = inlink->h;



    /* Make sure that the result is divisible by the factor we determined

     * earlier. If no factor was set, it is nothing will happen as the default

     * factor is 1 */

    if (w < 0)

        w = av_rescale(h, inlink->w, inlink->h * factor_w) * factor_w;

    if (h < 0)

        h = av_rescale(w, inlink->h, inlink->w * factor_h) * factor_h;



    *ret_w = w;

    *ret_h = h;



    return 0;



fail:

    av_log(log_ctx, AV_LOG_ERROR,

           "Error when evaluating the expression '%s'.\n"

           "Maybe the expression for out_w:'%s' or for out_h:'%s' is self-referencing.\n",

           expr, w_expr, h_expr);

    return ret;

}
