1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/js/src/ds/Sort.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,137 @@
1.4 +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
1.5 + * vim: set ts=8 sts=4 et sw=4 tw=99:
1.6 + * This Source Code Form is subject to the terms of the Mozilla Public
1.7 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.8 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.9 +
1.10 +#ifndef ds_Sort_h
1.11 +#define ds_Sort_h
1.12 +
1.13 +#include "jstypes.h"
1.14 +
1.15 +namespace js {
1.16 +
1.17 +namespace detail {
1.18 +
1.19 +template<typename T>
1.20 +MOZ_ALWAYS_INLINE void
1.21 +CopyNonEmptyArray(T *dst, const T *src, size_t nelems)
1.22 +{
1.23 + JS_ASSERT(nelems != 0);
1.24 + const T *end = src + nelems;
1.25 + do {
1.26 + *dst++ = *src++;
1.27 + } while (src != end);
1.28 +}
1.29 +
1.30 +/* Helper function for MergeSort. */
1.31 +template<typename T, typename Comparator>
1.32 +MOZ_ALWAYS_INLINE bool
1.33 +MergeArrayRuns(T *dst, const T *src, size_t run1, size_t run2, Comparator c)
1.34 +{
1.35 + JS_ASSERT(run1 >= 1);
1.36 + JS_ASSERT(run2 >= 1);
1.37 +
1.38 + /* Copy runs already in sorted order. */
1.39 + const T *b = src + run1;
1.40 + bool lessOrEqual;
1.41 + if (!c(b[-1], b[0], &lessOrEqual))
1.42 + return false;
1.43 +
1.44 + if (!lessOrEqual) {
1.45 + /* Runs are not already sorted, merge them. */
1.46 + for (const T *a = src;;) {
1.47 + if (!c(*a, *b, &lessOrEqual))
1.48 + return false;
1.49 + if (lessOrEqual) {
1.50 + *dst++ = *a++;
1.51 + if (!--run1) {
1.52 + src = b;
1.53 + break;
1.54 + }
1.55 + } else {
1.56 + *dst++ = *b++;
1.57 + if (!--run2) {
1.58 + src = a;
1.59 + break;
1.60 + }
1.61 + }
1.62 + }
1.63 + }
1.64 + CopyNonEmptyArray(dst, src, run1 + run2);
1.65 + return true;
1.66 +}
1.67 +
1.68 +} /* namespace detail */
1.69 +
1.70 +/*
1.71 + * Sort the array using the merge sort algorithm. The scratch should point to
1.72 + * a temporary storage that can hold nelems elements.
1.73 + *
1.74 + * The comparator must provide the () operator with the following signature:
1.75 + *
1.76 + * bool operator()(const T& a, const T& a, bool *lessOrEqualp);
1.77 + *
1.78 + * It should return true on success and set *lessOrEqualp to the result of
1.79 + * a <= b operation. If it returns false, the sort terminates immediately with
1.80 + * the false result. In this case the content of the array and scratch is
1.81 + * arbitrary.
1.82 + */
1.83 +template<typename T, typename Comparator>
1.84 +bool
1.85 +MergeSort(T *array, size_t nelems, T *scratch, Comparator c)
1.86 +{
1.87 + const size_t INS_SORT_LIMIT = 3;
1.88 +
1.89 + if (nelems <= 1)
1.90 + return true;
1.91 +
1.92 + /*
1.93 + * Apply insertion sort to small chunks to reduce the number of merge
1.94 + * passes needed.
1.95 + */
1.96 + for (size_t lo = 0; lo < nelems; lo += INS_SORT_LIMIT) {
1.97 + size_t hi = lo + INS_SORT_LIMIT;
1.98 + if (hi >= nelems)
1.99 + hi = nelems;
1.100 + for (size_t i = lo + 1; i != hi; i++) {
1.101 + for (size_t j = i; ;) {
1.102 + bool lessOrEqual;
1.103 + if (!c(array[j - 1], array[j], &lessOrEqual))
1.104 + return false;
1.105 + if (lessOrEqual)
1.106 + break;
1.107 + T tmp = array[j - 1];
1.108 + array[j - 1] = array[j];
1.109 + array[j] = tmp;
1.110 + if (--j == lo)
1.111 + break;
1.112 + }
1.113 + }
1.114 + }
1.115 +
1.116 + T *vec1 = array;
1.117 + T *vec2 = scratch;
1.118 + for (size_t run = INS_SORT_LIMIT; run < nelems; run *= 2) {
1.119 + for (size_t lo = 0; lo < nelems; lo += 2 * run) {
1.120 + size_t hi = lo + run;
1.121 + if (hi >= nelems) {
1.122 + detail::CopyNonEmptyArray(vec2 + lo, vec1 + lo, nelems - lo);
1.123 + break;
1.124 + }
1.125 + size_t run2 = (run <= nelems - hi) ? run : nelems - hi;
1.126 + if (!detail::MergeArrayRuns(vec2 + lo, vec1 + lo, run, run2, c))
1.127 + return false;
1.128 + }
1.129 + T *swap = vec1;
1.130 + vec1 = vec2;
1.131 + vec2 = swap;
1.132 + }
1.133 + if (vec1 == scratch)
1.134 + detail::CopyNonEmptyArray(array, scratch, nelems);
1.135 + return true;
1.136 +}
1.137 +
1.138 +} /* namespace js */
1.139 +
1.140 +#endif /* ds_Sort_h */
