Tweak quicksort loop to reduce number of compares slightly.

src/array.js

 // Copyright 2006-2008 the V8 project authors. All rights reserved.

[Karl Klose, 2010/12/20 14:28:43]

-2010

[Lasse Reichstein, 2010/12/20 15:00:59]

Will do.

 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
 //       with the distribution.
@@ skipping 658 matching lines @@
         } else {
           break;
         }
       }
       a[j + 1] = element;
     }
   }
 
   function QuickSort(a, from, to) {
     // Insertion sort is faster for short arrays.
-    if (to - from <= 13) {
+    if (to - from <= 10) {
       InsertionSort(a, from, to);
       return;
     }
-
     // Find a pivot as the median of first, last and middle element.
     var v0 = a[from];
     var v1 = a[to - 1];
     var middle_index = from + ((to - from) >> 1);
     var v2 = a[middle_index];
-    var c01 = comparefn(v0, v1);
+    var c01 = %_CallFunction(global_receiver, v0, v1, comparefn);
     if (c01 > 0) {
       // v1 < v0, so swap them.
       var tmp = v0;
       v0 = v1;
       v1 = tmp;
     } // v0 <= v1.
-    var c02 = comparefn(v0, v2);
+    var c02 = %_CallFunction(global_receiver, v0, v2, comparefn);
     if (c02 >= 0) {
       // v2 <= v0 <= v1.
       var tmp = v0;
       v0 = v2;
       v2 = v1;
       v1 = tmp;
     } else {
       // v0 <= v1 && v0 < v2
-      var c12 = comparefn(v1, v2);
+      var c12 = %_CallFunction(global_receiver, v1, v2, comparefn);
       if (c12 > 0) {
         // v0 <= v2 < v1
         var tmp = v1;
         v1 = v2;
         v2 = tmp;
       }
     }
     // v0 <= v1 <= v2
     a[from] = v0;
     a[to - 1] = v2;
     var pivot = v1;
-    var low_end = from + 1;   // Upper bound of the elements lower than pivot.
-    var high_start = to - 1;  // Lower bound of the elements greater than pivot.
+    var low_end = from + 1;   // Upper bound of elements lower than pivot.
+    var high_start = to - 1;  // Lower bound of elements greater than pivot.
     a[middle_index] = a[low_end];
     a[low_end] = pivot;
 
     // From low_end to i are elements equal to pivot.
     // From i to high_start are elements that haven't been compared yet.
-    for (var i = low_end + 1; i < high_start; ) {
+    partition: for (var i = low_end + 1; i < high_start; ) {

[Karl Klose, 2010/12/20 14:28:43]

Increase i here instead of at the end of the loop?

[Lasse Reichstein, 2010/12/20 15:00:59]

Good point!

       var element = a[i];
       var order = %_CallFunction(global_receiver, element, pivot, comparefn);
       if (order < 0) {
         %_SwapElements(a, i, low_end);
-        i++;
         low_end++;
       } else if (order > 0) {
-        high_start--;
+        do {
+          high_start--;
+          if (high_start == i) break partition;
+          var top_elem = a[high_start];
+          order = %_CallFunction(global_receiver, top_elem, pivot, comparefn);
+        } while (order > 0);
         %_SwapElements(a, i, high_start);
-      } else {  // order == 0
-        i++;
+        if (order < 0) {
+          %_SwapElements(a, i, low_end);
+          low_end++;
+        }
       }
+      i++;
     }
     QuickSort(a, from, low_end);
     QuickSort(a, high_start, to);
   }
 
   // Copy elements in the range 0..length from obj's prototype chain
   // to obj itself, if obj has holes. Return one more than the maximal index
   // of a prototype property.
   function CopyFromPrototype(obj, length) {
     var max = 0;
@@ skipping 456 matching lines @@
     "lastIndexOf", getFunction("lastIndexOf", ArrayLastIndexOf, 1),
     "reduce", getFunction("reduce", ArrayReduce, 1),
     "reduceRight", getFunction("reduceRight", ArrayReduceRight, 1)
   ));
 
   %FinishArrayPrototypeSetup($Array.prototype);
 }
 
 
 SetupArray();