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Tweak quicksort loop to reduce number of compares slightly.

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Review URL: http://codereview.chromium.org/6039002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6087 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
lrn@chromium.org 2010-12-20 14:57:51 +00:00
parent da934d1f26
commit 5741575327
2 changed files with 34 additions and 14 deletions
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31
src/array.js
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@ -1,4 +1,4 @@
// Copyright 2006-2008 the V8 project authors. All rights reserved.
// Copyright 2010 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
@ -677,24 +677,23 @@ function ArraySort(comparefn) {
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;
@ -703,7 +702,7 @@ function ArraySort(comparefn) {
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;
@ -715,25 +714,31 @@ function ArraySort(comparefn) {
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; i++) {
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++;
}
}
}
QuickSort(a, from, low_end);

17
test/mjsunit/array-sort.js
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@ -1,4 +1,4 @@
// Copyright 2008 the V8 project authors. All rights reserved.
// Copyright 2010 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
@ -360,3 +360,18 @@ function TestSpecialCasesInheritedElementSort() {
}
TestSpecialCasesInheritedElementSort();
// Test that sort calls compare function with global object as receiver,
// and with only elements of the array as arguments.
function o(v) {
return {__proto__: o.prototype, val: v};
}
var arr = [o(1), o(2), o(4), o(8), o(16), o(32), o(64), o(128), o(256), o(-0)];
var global = this;
function cmpTest(a, b) {
assertEquals(global, this);
assertTrue(a instanceof o);
assertTrue(b instanceof o);
return a.val - b.val;
}
arr.sort(cmpTest);