lavu/eval: add if() and ifnot() eval functions

They allow to implement the if/then/else logic, which cannot be
implemented otherwise.

For example the expression:
A*B + not(A)*C

always evaluates to NaN if B is NaN, even in the case where A is 0.

doc/eval.texi

@@ -98,6 +98,14 @@ point (@var{x}, @var{y}) from the origin.
 @item gcd(x, y)
 Return the greatest common divisor of @var{x} and @var{y}. If both @var{x} and
 @var{y} are 0 or either or both are less than zero then behavior is undefined.
+
+@item if(x, y)
+Evaluate @var{x}, and if the result is non-zero return the result of
+the evaluation of @var{y}, return 0 otherwise.
+
+@item ifnot(x, y)
+Evaluate @var{x}, and if the result is zero return the result of the
+evaluation of @var{y}, return 0 otherwise.
 @end table
 
 The following constants are available:
@@ -116,13 +124,13 @@ Note that:
 
 @code{+} works like OR
 
-thus
+and the construct:
 @example
 if A then B else C
 @end example
 is equivalent to
 @example
-A*B + not(A)*C
+if(A,B) + ifnot(A,C)
 @end example
 
 In your C code, you can extend the list of unary and binary functions,

libavutil/avutil.h

@@ -155,7 +155,7 @@
 
 #define LIBAVUTIL_VERSION_MAJOR 51
 #define LIBAVUTIL_VERSION_MINOR 34
-#define LIBAVUTIL_VERSION_MICRO 100
+#define LIBAVUTIL_VERSION_MICRO 101
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
                                                LIBAVUTIL_VERSION_MINOR, \

libavutil/eval.c

@@ -136,6 +136,7 @@ struct AVExpr {
         e_pow, e_mul, e_div, e_add,
         e_last, e_st, e_while, e_floor, e_ceil, e_trunc,
         e_sqrt, e_not, e_random, e_hypot, e_gcd,
+        e_if, e_ifnot,
     } type;
     double value; // is sign in other types
     union {
@@ -165,6 +166,8 @@ static double eval_expr(Parser *p, AVExpr *e)
         case e_trunc:  return e->value * trunc(eval_expr(p, e->param[0]));
         case e_sqrt:   return e->value * sqrt (eval_expr(p, e->param[0]));
         case e_not:    return e->value * (eval_expr(p, e->param[0]) == 0);
+        case e_if:     return e->value * ( eval_expr(p, e->param[0]) ? eval_expr(p, e->param[1]) : 0);
+        case e_ifnot:  return e->value * (!eval_expr(p, e->param[0]) ? eval_expr(p, e->param[1]) : 0);
         case e_random:{
             int idx= av_clip(eval_expr(p, e->param[0]), 0, VARS-1);
             uint64_t r= isnan(p->var[idx]) ? 0 : p->var[idx];
@@ -324,6 +327,8 @@ static int parse_primary(AVExpr **e, Parser *p)
     else if (strmatch(next, "random")) d->type = e_random;
     else if (strmatch(next, "hypot" )) d->type = e_hypot;
     else if (strmatch(next, "gcd"   )) d->type = e_gcd;
+    else if (strmatch(next, "if"    )) d->type = e_if;
+    else if (strmatch(next, "ifnot" )) d->type = e_ifnot;
     else {
         for (i=0; p->func1_names && p->func1_names[i]; i++) {
             if (strmatch(next, p->func1_names[i])) {
@@ -690,6 +695,9 @@ int main(int argc, char **argv)
         "pow(PI,1.23)",
         "PI^1.23",
         "pow(-1,1.23)",
+        "if(1, 2)",
+        "ifnot(0, 23)",
+        "ifnot(1, NaN) + if(0, 1)",
         NULL
     };
 

tests/ref/fate/eval

@@ -160,5 +160,14 @@ Evaluating 'PI^1.23'
 Evaluating 'pow(-1,1.23)'
 'pow(-1,1.23)' -> nan
 
+Evaluating 'if(1, 2)'
+'if(1, 2)' -> 2.000000
+
+Evaluating 'ifnot(0, 23)'
+'ifnot(0, 23)' -> 23.000000
+
+Evaluating 'ifnot(1, NaN) + if(0, 1)'
+'ifnot(1, NaN) + if(0, 1)' -> 0.000000
+
 12.700000 == 12.7
 0.931323 == 0.931322575