michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
michael@0:  * vim: set ts=8 sts=4 et sw=4 tw=99:
michael@0:  * This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef ds_Sort_h
michael@0: #define ds_Sort_h
michael@0: 
michael@0: #include "jstypes.h"
michael@0: 
michael@0: namespace js {
michael@0: 
michael@0: namespace detail {
michael@0: 
michael@0: template<typename T>
michael@0: MOZ_ALWAYS_INLINE void
michael@0: CopyNonEmptyArray(T *dst, const T *src, size_t nelems)
michael@0: {
michael@0:     JS_ASSERT(nelems != 0);
michael@0:     const T *end = src + nelems;
michael@0:     do {
michael@0:         *dst++ = *src++;
michael@0:     } while (src != end);
michael@0: }
michael@0: 
michael@0: /* Helper function for MergeSort. */
michael@0: template<typename T, typename Comparator>
michael@0: MOZ_ALWAYS_INLINE bool
michael@0: MergeArrayRuns(T *dst, const T *src, size_t run1, size_t run2, Comparator c)
michael@0: {
michael@0:     JS_ASSERT(run1 >= 1);
michael@0:     JS_ASSERT(run2 >= 1);
michael@0: 
michael@0:     /* Copy runs already in sorted order. */
michael@0:     const T *b = src + run1;
michael@0:     bool lessOrEqual;
michael@0:     if (!c(b[-1],  b[0], &lessOrEqual))
michael@0:         return false;
michael@0: 
michael@0:     if (!lessOrEqual) {
michael@0:         /* Runs are not already sorted, merge them. */
michael@0:         for (const T *a = src;;) {
michael@0:             if (!c(*a, *b, &lessOrEqual))
michael@0:                 return false;
michael@0:             if (lessOrEqual) {
michael@0:                 *dst++ = *a++;
michael@0:                 if (!--run1) {
michael@0:                     src = b;
michael@0:                     break;
michael@0:                 }
michael@0:             } else {
michael@0:                 *dst++ = *b++;
michael@0:                 if (!--run2) {
michael@0:                     src = a;
michael@0:                     break;
michael@0:                 }
michael@0:             }
michael@0:         }
michael@0:     }
michael@0:     CopyNonEmptyArray(dst, src, run1 + run2);
michael@0:     return true;
michael@0: }
michael@0: 
michael@0: } /* namespace detail */
michael@0: 
michael@0: /*
michael@0:  * Sort the array using the merge sort algorithm. The scratch should point to
michael@0:  * a temporary storage that can hold nelems elements.
michael@0:  *
michael@0:  * The comparator must provide the () operator with the following signature:
michael@0:  *
michael@0:  *     bool operator()(const T& a, const T& a, bool *lessOrEqualp);
michael@0:  *
michael@0:  * It should return true on success and set *lessOrEqualp to the result of
michael@0:  * a <= b operation. If it returns false, the sort terminates immediately with
michael@0:  * the false result. In this case the content of the array and scratch is
michael@0:  * arbitrary.
michael@0:  */
michael@0: template<typename T, typename Comparator>
michael@0: bool
michael@0: MergeSort(T *array, size_t nelems, T *scratch, Comparator c)
michael@0: {
michael@0:     const size_t INS_SORT_LIMIT = 3;
michael@0: 
michael@0:     if (nelems <= 1)
michael@0:         return true;
michael@0: 
michael@0:     /*
michael@0:      * Apply insertion sort to small chunks to reduce the number of merge
michael@0:      * passes needed.
michael@0:      */
michael@0:     for (size_t lo = 0; lo < nelems; lo += INS_SORT_LIMIT) {
michael@0:         size_t hi = lo + INS_SORT_LIMIT;
michael@0:         if (hi >= nelems)
michael@0:             hi = nelems;
michael@0:         for (size_t i = lo + 1; i != hi; i++) {
michael@0:             for (size_t j = i; ;) {
michael@0:                 bool lessOrEqual;
michael@0:                 if (!c(array[j - 1], array[j], &lessOrEqual))
michael@0:                     return false;
michael@0:                 if (lessOrEqual)
michael@0:                     break;
michael@0:                 T tmp = array[j - 1];
michael@0:                 array[j - 1] = array[j];
michael@0:                 array[j] = tmp;
michael@0:                 if (--j == lo)
michael@0:                     break;
michael@0:             }
michael@0:         }
michael@0:     }
michael@0: 
michael@0:     T *vec1 = array;
michael@0:     T *vec2 = scratch;
michael@0:     for (size_t run = INS_SORT_LIMIT; run < nelems; run *= 2) {
michael@0:         for (size_t lo = 0; lo < nelems; lo += 2 * run) {
michael@0:             size_t hi = lo + run;
michael@0:             if (hi >= nelems) {
michael@0:                 detail::CopyNonEmptyArray(vec2 + lo, vec1 + lo, nelems - lo);
michael@0:                 break;
michael@0:             }
michael@0:             size_t run2 = (run <= nelems - hi) ? run : nelems - hi;
michael@0:             if (!detail::MergeArrayRuns(vec2 + lo, vec1 + lo, run, run2, c))
michael@0:                 return false;
michael@0:         }
michael@0:         T *swap = vec1;
michael@0:         vec1 = vec2;
michael@0:         vec2 = swap;
michael@0:     }
michael@0:     if (vec1 == scratch)
michael@0:         detail::CopyNonEmptyArray(array, scratch, nelems);
michael@0:     return true;
michael@0: }
michael@0: 
michael@0: } /* namespace js */
michael@0: 
michael@0: #endif /* ds_Sort_h */