+struct ff_expr_s {
+ enum {
+ e_value, e_const, e_func0, e_func1, e_func2,
+ e_squish, e_gauss, e_ld,
+ e_mod, e_max, e_min, e_eq, e_gt, e_gte,
+ e_pow, e_mul, e_div, e_add,
+ e_last, e_st, e_while,
+ } type;
+ double value; // is sign in other types
+ union {
+ int const_index;
+ double (*func0)(double);
+ double (*func1)(void *, double);
+ double (*func2)(void *, double, double);
+ } a;
+ AVEvalExpr * param[2];
+};
+
+static double eval_expr(Parser * p, AVEvalExpr * e) {
+ switch (e->type) {
+ case e_value: return e->value;
+ case e_const: return e->value * p->const_value[e->a.const_index];
+ case e_func0: return e->value * e->a.func0(eval_expr(p, e->param[0]));
+ case e_func1: return e->value * e->a.func1(p->opaque, eval_expr(p, e->param[0]));
+ case e_func2: return e->value * e->a.func2(p->opaque, eval_expr(p, e->param[0]), eval_expr(p, e->param[1]));
+ case e_squish: return 1/(1+exp(4*eval_expr(p, e->param[0])));
+ case e_gauss: { double d = eval_expr(p, e->param[0]); return exp(-d*d/2)/sqrt(2*M_PI); }
+ case e_ld: return e->value * p->var[av_clip(eval_expr(p, e->param[0]), 0, VARS-1)];
+ case e_while: {
+ double d = NAN;
+ while(eval_expr(p, e->param[0]))
+ d=eval_expr(p, e->param[1]);
+ return d;
+ }
+ default: {
+ double d = eval_expr(p, e->param[0]);
+ double d2 = eval_expr(p, e->param[1]);
+ switch (e->type) {
+ case e_mod: return e->value * (d - floor(d/d2)*d2);
+ case e_max: return e->value * (d > d2 ? d : d2);
+ case e_min: return e->value * (d < d2 ? d : d2);
+ case e_eq: return e->value * (d == d2 ? 1.0 : 0.0);
+ case e_gt: return e->value * (d > d2 ? 1.0 : 0.0);
+ case e_gte: return e->value * (d >= d2 ? 1.0 : 0.0);
+ case e_pow: return e->value * pow(d, d2);
+ case e_mul: return e->value * (d * d2);
+ case e_div: return e->value * (d / d2);
+ case e_add: return e->value * (d + d2);
+ case e_last:return e->value * d2;
+ case e_st : return e->value * (p->var[av_clip(d, 0, VARS-1)]= d2);
+ }
+ }
+ }
+ return NAN;
+}
+
+static AVEvalExpr * parse_expr(Parser *p);
+
+void ff_eval_free(AVEvalExpr * e) {
+ if (!e) return;
+ ff_eval_free(e->param[0]);
+ ff_eval_free(e->param[1]);
+ av_freep(&e);
+}
+
+static AVEvalExpr * parse_primary(Parser *p) {
+ AVEvalExpr * d = av_mallocz(sizeof(AVEvalExpr));