1 files changed, 14 insertions, 0 deletions
diff --git a/src/preamble.js b/src/preamble.js
index 24049283..6f4b49de 100644
--- a/src/preamble.js
+++ b/src/preamble.js
@@ -748,6 +748,20 @@ Module['writeArrayToMemory'] = writeArrayToMemory;
 {{{ unSign }}}
 {{{ reSign }}}
 
+#if PRECISE_I32_MUL
+if (!Math.imul) Math.imul = function(a, b) {
+  var ah  = a >>> 16;
+  var al = a & 0xffff;
+  var bh  = b >>> 16;
+  var bl = b & 0xffff;
+  return (al*bl + ((ah*bl + al*bh) << 16))|0;
+};
+#else
+Math.imul = function(a, b) {
+  return (a*b)|0; // fast but imprecise
+};
+#endif
+
 // A counter of dependencies for calling run(). If we need to
 // do asynchronous work before running, increment this and
 // decrement it. Incrementing must happen in a place like