99 lines
2.6 KiB
C
99 lines
2.6 KiB
C
/* -*-comment-start: "//";comment-end:""-*-
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* GNU Mes --- Maxwell Equations of Software
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* Copyright © 2017,2018 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
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*
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* This file is part of GNU Mes.
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*
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* GNU Mes is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or (at
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* your option) any later version.
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*
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* GNU Mes is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GNU Mes. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <stdlib.h>
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void
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qswap (void *a, void *b, size_t size)
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{
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char *pa = a;
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char *pb = b;
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do
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{
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char tmp = *pa;
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*pa++ = *pb;
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*pb++ = tmp;
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} while (--size > 0);
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}
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size_t
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qpart (void *base, size_t low, size_t high, size_t size,
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int (*compare) (void const *, void const *))
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{
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char *pbase = base;
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// select the rightmost element as pivot
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void *pivot = pbase + high * size;
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// pointer for greater element
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size_t i = (low - 1);
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// traverse each element of the array
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// compare them with the pivot
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for (int j = low; j < high; j++)
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{
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int c = compare (pbase + j * size, pivot);
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if (c < 0)
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{
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// if element smaller than pivot is found
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// swap it with the greater element pointed by i
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i++;
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// swap element at i with element at j
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void *p1 = pbase + i * size;
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void *p2 = pbase + j * size;
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qswap (p1, p2, size);
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}
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}
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// swap the pivot element with the greater element at i
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void *p1 = pbase + (i + 1) * size;
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void *p2 = pbase + high * size;
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qswap (p1, p2, size);
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// return the qpart point
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return (i + 1);
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}
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void
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_qsort (void *base, size_t low, size_t high, size_t size,
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int (*compare) (void const *, void const *))
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{
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if (low >= high)
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return;
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// find the pivot element such that
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// elements smaller than pivot are on left of pivot
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// elements greater than pivot are on right of pivot
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int pi = qpart (base, low, high, size, compare);
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// recursive call on the left of pivot
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_qsort (base, low, pi - 1, size, compare);
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// recursive call on the right of pivot
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_qsort (base, pi + 1, high, size, compare);
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}
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void
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qsort (void *base, size_t count, size_t size,
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int (*compare) (void const *, void const *))
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{
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_qsort (base, 0, count, size, compare);
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}
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