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New module 'array-mergesort'.
This commit is contained in:
Bruno Haible
@@ -1,3 +1,9 @@
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2009-02-15 Bruno Haible <bruno@clisp.org>
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New module 'array-mergesort'.
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* modules/array-mergesort: New file.
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* lib/array-mergesort.h: New file.
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2009-02-15 Bruno Haible <bruno@clisp.org>
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Fix 2009-02-07 commit.
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274
lib/array-mergesort.h
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274
lib/array-mergesort.h
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/* Stable-sorting of an array using mergesort.
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Copyright (C) 2009 Free Software Foundation, Inc.
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Written by Bruno Haible <bruno@clisp.org>, 2009.
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This program is free software: you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published
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by the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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/* This file implements stable sorting of an array, using the mergesort
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algorithm.
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Worst-case running time for an array of length N is O(N log N).
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Unlike the mpsort module, the algorithm here attempts to minimize not
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only the number of comparisons, but also the number of copying operations.
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Before including this file, you need to define
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ELEMENT The type of every array element.
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COMPARE A two-argument macro that takes two 'const ELEMENT *'
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pointers and returns a negative, zero, or positive 'int'
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value if the element pointed to by the first argument is,
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respectively, less, equal, or greater than the element
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pointed to by the second argument.
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STATIC The storage class of the functions being defined.
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Before including this file, you also need to include:
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#include <stddef.h>
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*/
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/* Merge the sorted arrays src1[0..n1-1] and src2[0..n2-1] into
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dst[0..n1+n2-1]. In case of ambiguity, put the elements of src1
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before the elements of src2.
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n1 and n2 must be > 0.
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The arrays src1 and src2 must not overlap the dst array, except that
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src1 may be dst[n2..n1+n2-1], or src2 may be dst[n1..n1+n2-1]. */
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static void
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merge (const ELEMENT *src1, size_t n1,
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const ELEMENT *src2, size_t n2,
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ELEMENT *dst)
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{
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for (;;) /* while (n1 > 0 && n2 > 0) */
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{
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if (COMPARE (src1, src2) <= 0)
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{
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*dst++ = *src1++;
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n1--;
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if (n1 == 0)
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break;
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}
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else
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{
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*dst++ = *src2++;
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n2--;
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if (n2 == 0)
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break;
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}
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}
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/* Here n1 == 0 || n2 == 0 but also n1 > 0 || n2 > 0. */
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if (n1 > 0)
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{
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if (dst != src1)
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do
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{
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*dst++ = *src1++;
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n1--;
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}
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while (n1 > 0);
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}
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else /* n2 > 0 */
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{
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if (dst != src2)
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do
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{
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*dst++ = *src2++;
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n2--;
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}
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while (n2 > 0);
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}
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}
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/* Sort src[0..n-1] into dst[0..n-1], using tmp[0..n/2-1] as temporary
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(scratch) storage.
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The arrays src, dst, tmp must not overlap. */
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STATIC void
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merge_sort_fromto (const ELEMENT *src, ELEMENT *dst, size_t n, ELEMENT *tmp)
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{
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switch (n)
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{
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case 0:
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return;
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case 1:
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/* Nothing to do. */
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dst[0] = src[0];
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return;
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case 2:
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/* Trivial case. */
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if (COMPARE (&src[0], &src[1]) <= 0)
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{
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/* src[0] <= src[1] */
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dst[0] = src[0];
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dst[1] = src[1];
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}
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else
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{
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dst[0] = src[1];
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dst[1] = src[0];
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}
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break;
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case 3:
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/* Simple case. */
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if (COMPARE (&src[0], &src[1]) <= 0)
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{
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if (COMPARE (&src[1], &src[2]) <= 0)
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{
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/* src[0] <= src[1] <= src[2] */
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dst[0] = src[0];
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dst[1] = src[1];
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dst[2] = src[2];
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}
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else if (COMPARE (&src[0], &src[2]) <= 0)
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{
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/* src[0] <= src[2] < src[1] */
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dst[0] = src[0];
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dst[1] = src[2];
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dst[2] = src[1];
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}
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else
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{
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/* src[2] < src[0] <= src[1] */
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dst[0] = src[2];
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dst[1] = src[0];
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dst[2] = src[1];
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}
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}
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else
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{
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if (COMPARE (&src[0], &src[2]) <= 0)
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{
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/* src[1] < src[0] <= src[2] */
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dst[0] = src[1];
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dst[1] = src[0];
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dst[2] = src[2];
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}
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else if (COMPARE (&src[1], &src[2]) <= 0)
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{
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/* src[1] <= src[2] < src[0] */
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dst[0] = src[1];
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dst[1] = src[2];
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dst[2] = src[0];
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}
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else
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{
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/* src[2] < src[1] < src[0] */
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dst[0] = src[2];
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dst[1] = src[1];
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dst[2] = src[0];
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}
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}
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break;
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default:
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{
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size_t n1 = n / 2;
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size_t n2 = (n + 1) / 2;
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/* Note: n1 + n2 = n, n1 <= n2. */
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/* Sort src[n1..n-1] into dst[n1..n-1], scratching tmp[0..n2/2-1]. */
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merge_sort_fromto (src + n1, dst + n1, n2, tmp);
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/* Sort src[0..n1-1] into tmp[0..n1-1], scratching dst[0..n1-1]. */
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merge_sort_fromto (src, tmp, n1, dst);
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/* Merge the two half results. */
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merge (tmp, n1, dst + n1, n2, dst);
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}
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break;
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}
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}
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/* Sort src[0..n-1], using tmp[0..n-1] as temporary (scratch) storage.
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The arrays src, tmp must not overlap. */
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STATIC void
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merge_sort_inplace (ELEMENT *src, size_t n, ELEMENT *tmp)
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{
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switch (n)
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{
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case 0:
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case 1:
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/* Nothing to do. */
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return;
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case 2:
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/* Trivial case. */
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if (COMPARE (&src[0], &src[1]) <= 0)
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{
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/* src[0] <= src[1] */
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}
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else
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{
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ELEMENT t = src[0];
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src[0] = src[1];
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src[1] = t;
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}
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break;
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case 3:
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/* Simple case. */
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if (COMPARE (&src[0], &src[1]) <= 0)
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{
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if (COMPARE (&src[1], &src[2]) <= 0)
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{
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/* src[0] <= src[1] <= src[2] */
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}
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else if (COMPARE (&src[0], &src[2]) <= 0)
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{
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/* src[0] <= src[2] < src[1] */
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ELEMENT t = src[1];
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src[1] = src[2];
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src[2] = t;
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}
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else
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{
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/* src[2] < src[0] <= src[1] */
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ELEMENT t = src[0];
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src[0] = src[2];
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src[2] = src[1];
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src[1] = t;
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}
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}
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else
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{
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if (COMPARE (&src[0], &src[2]) <= 0)
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{
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/* src[1] < src[0] <= src[2] */
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ELEMENT t = src[0];
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src[0] = src[1];
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src[1] = t;
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}
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else if (COMPARE (&src[1], &src[2]) <= 0)
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{
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/* src[1] <= src[2] < src[0] */
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ELEMENT t = src[0];
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src[0] = src[1];
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src[1] = src[2];
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src[2] = t;
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}
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else
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{
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/* src[2] < src[1] < src[0] */
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ELEMENT t = src[0];
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src[0] = src[2];
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src[2] = t;
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}
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}
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break;
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default:
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{
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size_t n1 = n / 2;
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size_t n2 = (n + 1) / 2;
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/* Note: n1 + n2 = n, n1 <= n2. */
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/* Sort src[n1..n-1], scratching tmp[0..n2-1]. */
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merge_sort_inplace (src + n1, n2, tmp);
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/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2*n1-1]. */
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merge_sort_fromto (src, tmp, n1, tmp + n1);
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/* Merge the two half results. */
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merge (tmp, n1, src + n1, n2, src);
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}
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break;
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}
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}
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#undef ELEMENT
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#undef COMPARE
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#undef STATIC
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21
modules/array-mergesort
Normal file
21
modules/array-mergesort
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@@ -0,0 +1,21 @@
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Description:
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Merge-sort algorithm on arrays.
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Files:
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lib/array-mergesort.h
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Depends-on:
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configure.ac:
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Makefile.am:
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Include:
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"array-mergesort.h"
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License:
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LGPL
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Maintainer:
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Bruno Haible
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