Math.imul

Author: matthewleon

src/Math.js

@@ -24,6 +24,27 @@ exports.exp = Math.exp;
 
 exports.floor = Math.floor;
 
+function nativeImul(a) {
+  return function (b) {
+    return Math.imul(a, b);
+  };
+}
+
+// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/imul
+function emulatedImul(a) {
+  return function (b) {
+    var ah = (a >>> 16) & 0xffff;
+    var al = a & 0xffff;
+    var bh = (b >>> 16) & 0xffff;
+    var bl = b & 0xffff;
+    // the shift by 0 fixes the sign on the high part
+    // the final |0 converts the unsigned value into a signed value
+    return (al * bl) + (((ah * bl + al * bh) << 16) >>> 0) | 0;
+  };
+}
+
+exports.imul = Math.imul ? nativeImul : emulatedImul;
+
 exports.trunc = Math.trunc || function (n) {
   return n < 0 ? Math.ceil(n) : Math.floor(n);
 };

src/Math.purs

@@ -36,6 +36,9 @@ foreign import exp :: Number -> Number
 -- | Returns the largest integer not larger than the argument.
 foreign import floor :: Number -> Number
 
+-- | Returns the result of the C-like 32-bit multiplication of the two arguments.
+foreign import imul :: Int -> Int -> Int
+
 -- | Returns the natural logarithm of a number.
 foreign import log :: Number -> Number