added Magic.threemult to use 3+3 complex-multiply variant when possible

[empty commit message]

genfft/complex.ml

@@ -48,9 +48,20 @@ let nan x = CE (NaN x, makeNum Number.zero)
 
 let half = inverse_int 2
 
+let times3x3 (CE (a, b)) (CE (c, d)) = 
+  CE (makePlus [makeTimes (c, makePlus [a; makeUminus (b)]);
+	        makeTimes (b, makePlus [c; makeUminus (d)])],
+      makePlus [makeTimes (a, makePlus [c; d]);
+	        makeUminus(makeTimes (c, makePlus [a; makeUminus (b)]))])
+
 let times (CE (a, b)) (CE (c, d)) = 
-  CE (makePlus [makeTimes (a, c); makeUminus (makeTimes (b, d))],
-      makePlus [makeTimes (a, d); makeTimes (b, c)])
+  if not !Magic.threemult then
+    CE (makePlus [makeTimes (a, c); makeUminus (makeTimes (b, d))],
+        makePlus [makeTimes (a, d); makeTimes (b, c)])
+  else if is_constant c && is_constant d then
+    times3x3 (CE (a, b)) (CE (c, d))
+  else (* hope a and b are constant expressions *)
+    times3x3 (CE (c, d)) (CE (a, b))
 
 let ctimes (CE (a, _)) (CE (c, _)) = 
   CE (CTimes (a, c), makeNum Number.zero)

genfft/magic.ml

@@ -28,6 +28,7 @@ let circular_min = ref 64
 let rader_min = ref 13
 let rader_list = ref [5]
 let alternate_convolution = ref 17
+let threemult = ref false
 let inline_single = ref true
 let inline_loads = ref false
 let inline_loads_constants = ref false
@@ -78,6 +79,9 @@ let speclist = [
   "-rader-min", set_int rader_min,
   "<n> : Use Rader's algorithm for prime sizes >= <n>";
 
+  "-threemult", set_bool threemult, 
+  " Use 3-multiply complex multiplications";
+
   "-karatsuba-min", set_int karatsuba_min, undocumented;
   "-karatsuba-variant", set_int karatsuba_variant, undocumented;
   "-circular-min", set_int circular_min, undocumented;