optimize memory alignment calculations

2 files changed, 9 insertions, 2 deletions

diff --git a/src/runtime.js b/src/runtime.js
index 39aed12c..190260e6 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -101,11 +101,14 @@ var Runtime = {
 
   forceAlign: function(target, quantum) {
     quantum = quantum || {{{ QUANTUM_SIZE }}};
+    if (quantum == 1) return target;
     if (isNumber(target) && isNumber(quantum)) {
       return Math.ceil(target/quantum)*quantum;
-    } else {
-      return 'Math.ceil((' + target + ')/' + quantum + ')*' + quantum;
+    } else if (isNumber(quantum) && isPowerOfTwo(quantum)) {
+      var logg = log2(quantum);
+      return '((((' +target + ')+' + (quantum-1) + ')>>' + logg + ')<<' + logg + ')';
     }
+    return 'Math.ceil((' + target + ')/' + quantum + ')*' + quantum;
   },
 
   isNumberType: function(type) {
diff --git a/src/utility.js b/src/utility.js
index 4ffe46a0..5ddccfd4 100644
--- a/src/utility.js
+++ b/src/utility.js
@@ -297,6 +297,10 @@ function log2(x) {
   return Math.log(x)/Math.LN2;
 }
 
+function isPowerOfTwo(x) {
+  return x > 0 && ((x & (x-1)) == 0);
+}
+
 function Benchmarker() {
   var starts = {}, times = {}, counts = {};
   this.start = function(id) {