Mercurial > hg > octave-kai > gnulib-hg
changeset 11167:d11190b43f68
New module 'array-mergesort'.
author | Bruno Haible <bruno@clisp.org> |
---|---|
date | Mon, 16 Feb 2009 03:14:41 +0100 |
parents | 66432f187008 |
children | 8efaede722cf |
files | ChangeLog lib/array-mergesort.h modules/array-mergesort |
diffstat | 3 files changed, 301 insertions(+), 0 deletions(-) [+] |
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--- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,9 @@ +2009-02-15 Bruno Haible <bruno@clisp.org> + + New module 'array-mergesort'. + * modules/array-mergesort: New file. + * lib/array-mergesort.h: New file. + 2009-02-15 Bruno Haible <bruno@clisp.org> Fix 2009-02-07 commit.
new file mode 100644 --- /dev/null +++ b/lib/array-mergesort.h @@ -0,0 +1,274 @@ +/* Stable-sorting of an array using mergesort. + Copyright (C) 2009 Free Software Foundation, Inc. + Written by Bruno Haible <bruno@clisp.org>, 2009. + + This program is free software: you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published + by the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with this program. If not, see <http://www.gnu.org/licenses/>. */ + +/* This file implements stable sorting of an array, using the mergesort + algorithm. + Worst-case running time for an array of length N is O(N log N). + Unlike the mpsort module, the algorithm here attempts to minimize not + only the number of comparisons, but also the number of copying operations. + + Before including this file, you need to define + ELEMENT The type of every array element. + COMPARE A two-argument macro that takes two 'const ELEMENT *' + pointers and returns a negative, zero, or positive 'int' + value if the element pointed to by the first argument is, + respectively, less, equal, or greater than the element + pointed to by the second argument. + STATIC The storage class of the functions being defined. + Before including this file, you also need to include: + #include <stddef.h> + */ + +/* Merge the sorted arrays src1[0..n1-1] and src2[0..n2-1] into + dst[0..n1+n2-1]. In case of ambiguity, put the elements of src1 + before the elements of src2. + n1 and n2 must be > 0. + The arrays src1 and src2 must not overlap the dst array, except that + src1 may be dst[n2..n1+n2-1], or src2 may be dst[n1..n1+n2-1]. */ +static void +merge (const ELEMENT *src1, size_t n1, + const ELEMENT *src2, size_t n2, + ELEMENT *dst) +{ + for (;;) /* while (n1 > 0 && n2 > 0) */ + { + if (COMPARE (src1, src2) <= 0) + { + *dst++ = *src1++; + n1--; + if (n1 == 0) + break; + } + else + { + *dst++ = *src2++; + n2--; + if (n2 == 0) + break; + } + } + /* Here n1 == 0 || n2 == 0 but also n1 > 0 || n2 > 0. */ + if (n1 > 0) + { + if (dst != src1) + do + { + *dst++ = *src1++; + n1--; + } + while (n1 > 0); + } + else /* n2 > 0 */ + { + if (dst != src2) + do + { + *dst++ = *src2++; + n2--; + } + while (n2 > 0); + } +} + +/* Sort src[0..n-1] into dst[0..n-1], using tmp[0..n/2-1] as temporary + (scratch) storage. + The arrays src, dst, tmp must not overlap. */ +STATIC void +merge_sort_fromto (const ELEMENT *src, ELEMENT *dst, size_t n, ELEMENT *tmp) +{ + switch (n) + { + case 0: + return; + case 1: + /* Nothing to do. */ + dst[0] = src[0]; + return; + case 2: + /* Trivial case. */ + if (COMPARE (&src[0], &src[1]) <= 0) + { + /* src[0] <= src[1] */ + dst[0] = src[0]; + dst[1] = src[1]; + } + else + { + dst[0] = src[1]; + dst[1] = src[0]; + } + break; + case 3: + /* Simple case. */ + if (COMPARE (&src[0], &src[1]) <= 0) + { + if (COMPARE (&src[1], &src[2]) <= 0) + { + /* src[0] <= src[1] <= src[2] */ + dst[0] = src[0]; + dst[1] = src[1]; + dst[2] = src[2]; + } + else if (COMPARE (&src[0], &src[2]) <= 0) + { + /* src[0] <= src[2] < src[1] */ + dst[0] = src[0]; + dst[1] = src[2]; + dst[2] = src[1]; + } + else + { + /* src[2] < src[0] <= src[1] */ + dst[0] = src[2]; + dst[1] = src[0]; + dst[2] = src[1]; + } + } + else + { + if (COMPARE (&src[0], &src[2]) <= 0) + { + /* src[1] < src[0] <= src[2] */ + dst[0] = src[1]; + dst[1] = src[0]; + dst[2] = src[2]; + } + else if (COMPARE (&src[1], &src[2]) <= 0) + { + /* src[1] <= src[2] < src[0] */ + dst[0] = src[1]; + dst[1] = src[2]; + dst[2] = src[0]; + } + else + { + /* src[2] < src[1] < src[0] */ + dst[0] = src[2]; + dst[1] = src[1]; + dst[2] = src[0]; + } + } + break; + default: + { + size_t n1 = n / 2; + size_t n2 = (n + 1) / 2; + /* Note: n1 + n2 = n, n1 <= n2. */ + /* Sort src[n1..n-1] into dst[n1..n-1], scratching tmp[0..n2/2-1]. */ + merge_sort_fromto (src + n1, dst + n1, n2, tmp); + /* Sort src[0..n1-1] into tmp[0..n1-1], scratching dst[0..n1-1]. */ + merge_sort_fromto (src, tmp, n1, dst); + /* Merge the two half results. */ + merge (tmp, n1, dst + n1, n2, dst); + } + break; + } +} + +/* Sort src[0..n-1], using tmp[0..n-1] as temporary (scratch) storage. + The arrays src, tmp must not overlap. */ +STATIC void +merge_sort_inplace (ELEMENT *src, size_t n, ELEMENT *tmp) +{ + switch (n) + { + case 0: + case 1: + /* Nothing to do. */ + return; + case 2: + /* Trivial case. */ + if (COMPARE (&src[0], &src[1]) <= 0) + { + /* src[0] <= src[1] */ + } + else + { + ELEMENT t = src[0]; + src[0] = src[1]; + src[1] = t; + } + break; + case 3: + /* Simple case. */ + if (COMPARE (&src[0], &src[1]) <= 0) + { + if (COMPARE (&src[1], &src[2]) <= 0) + { + /* src[0] <= src[1] <= src[2] */ + } + else if (COMPARE (&src[0], &src[2]) <= 0) + { + /* src[0] <= src[2] < src[1] */ + ELEMENT t = src[1]; + src[1] = src[2]; + src[2] = t; + } + else + { + /* src[2] < src[0] <= src[1] */ + ELEMENT t = src[0]; + src[0] = src[2]; + src[2] = src[1]; + src[1] = t; + } + } + else + { + if (COMPARE (&src[0], &src[2]) <= 0) + { + /* src[1] < src[0] <= src[2] */ + ELEMENT t = src[0]; + src[0] = src[1]; + src[1] = t; + } + else if (COMPARE (&src[1], &src[2]) <= 0) + { + /* src[1] <= src[2] < src[0] */ + ELEMENT t = src[0]; + src[0] = src[1]; + src[1] = src[2]; + src[2] = t; + } + else + { + /* src[2] < src[1] < src[0] */ + ELEMENT t = src[0]; + src[0] = src[2]; + src[2] = t; + } + } + break; + default: + { + size_t n1 = n / 2; + size_t n2 = (n + 1) / 2; + /* Note: n1 + n2 = n, n1 <= n2. */ + /* Sort src[n1..n-1], scratching tmp[0..n2-1]. */ + merge_sort_inplace (src + n1, n2, tmp); + /* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2*n1-1]. */ + merge_sort_fromto (src, tmp, n1, tmp + n1); + /* Merge the two half results. */ + merge (tmp, n1, src + n1, n2, src); + } + break; + } +} + +#undef ELEMENT +#undef COMPARE +#undef STATIC