Rewrite the full pi constant as acos(-1.) (#66)

src/parse.fs

@@ -59,6 +59,7 @@ module private ParseImpl =
 
     let anyNumber =
         let n = (hexa <|> octal <|> number) <?> "number"
+        // number suffixes: float, long float, unsigned, long, half. FIXME: test the last two
         let suffix = ["f"; "F"; "LF"; "lf"; "u"; "U"; "l"; "L"; "h"; "H"]
                      |> List.map str |> choice
         let suffix = suffix <?> "suffix"

src/rewriter.fs

@@ -136,6 +136,11 @@ let rec private simplifyExpr env = function
         | Some (_, _, Some init) -> init
         | _ -> e
 
+    // pi is acos(-1), pi/2 is acos(0)
+    | Float(f, _) when f = 3.141592653589793 -> FunCall(Var "acos", [Float (-1., "")])
+    | Float(f, _) when f = 6.283185307179586 -> FunCall(Op "*", [Float (2., ""); FunCall(Var "acos", [Float (-1., "")])])
+    | Float(f, _) when f = 1.5707963267948966 -> FunCall(Var "acos", [Float (0., "")])
+
     | e -> e
 
 // Squeeze declarations: "float a=2.; float b;" => "float a=2.,b;"

tests/commands.txt

@@ -26,3 +26,7 @@
 -o tests/real/yx_long_way_from_home.frag.expected tests/real/yx_long_way_from_home.frag
 -o tests/real/oscars_chair.frag.expected tests/real/oscars_chair.frag
 -o tests/real/the_real_party_is_in_your_pocket.frag.expected tests/real/the_real_party_is_in_your_pocket.frag
+
+# Optimization tests
+
+--no-renaming --format text -o tests/unit/pi.frag.expected tests/unit/pi.frag

tests/unit/pi.frag

@@ -0,0 +1,10 @@
+
+void main() {
+    double pi = 3.141592653589793;
+    double minus_pi = -3.141592653589793;
+    double tau = 6.283185307179586;
+    double minus_tau = -6.283185307179586;
+    double half_pi = 1.5707963267948966;
+    double minus_half_pi = -1.5707963267948966;
+    double precise_pi = 3.14159265358979323846264338327950288419716939937510;
+}

tests/unit/pi.frag.expected

@@ -0,0 +1 @@
+void main(){double pi=acos(-1.),minus_pi=-acos(-1.),tau=2.*acos(-1.),minus_tau=-(2.*acos(-1.)),half_pi=acos(0.),minus_half_pi=-acos(0.),precise_pi=acos(-1.);}