@@ -99,6 +99,16 @@ 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.

 @end table

+The following constants are available:

+@table @option

+@item PI

+area of the unit disc, approximatively 3.14

+@item E

+exp(1) (Euler's number), approximatively 2.718

+@item PHI

+golden ratio (1+sqrt(5))/2, approximatively 1.618

+@end table

+

 Note that:

 @code{*} works like AND

@@ -72,6 +72,15 @@ static const int8_t si_prefixes['z' - 'E' + 1] = {

     ['Y'-'E']=  24,

 };

+static const struct {

+    const char *name;

+    double value;

+} constants[] = {

+    { "E",   M_E   },

+    { "PI",  M_PI  },

+    { "PHI", M_PHI },

+};

+

 double av_strtod(const char *numstr, char **tail)

 {

     double d;

@@ -233,6 +242,15 @@ static int parse_primary(AVExpr **e, Parser *p)

             return 0;

         }

     }

+    for (i = 0; i < FF_ARRAY_ELEMS(constants); i++) {

+        if (strmatch(p->s, constants[i].name)) {

+            p->s += strlen(constants[i].name);

+            d->type = e_value;

+            d->value = constants[i].value;

+            *e = d;

+            return 0;

+        }

+    }

     p->s= strchr(p->s, '(');

     if (p->s==NULL) {