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authorRich Felker <dalias@aerifal.cx>2011-04-27 13:27:04 -0400
committerRich Felker <dalias@aerifal.cx>2011-04-27 13:27:04 -0400
commit22263709eda9f7d692a0f484fd759f757418dbd7 (patch)
tree0a801dc54d32eb32e5104377909da1283cdea72c /src
parent4bb9b4f3b4a6794da3091f58acbd938ff66fc15b (diff)
downloadmusl-22263709eda9f7d692a0f484fd759f757418dbd7.tar.gz
replace heap sort with smoothsort implementation by Valentin Ochs
Smoothsort is an adaptive variant of heapsort. This version was written by Valentin Ochs (apo) specifically for inclusion in musl. I worked with him to get it working in O(1) memory usage even with giant array element widths, and to optimize it heavily for size and speed. It's still roughly 4 times as large as the old heap sort implementation, but roughly 20 times faster given an almost-sorted array of 1M elements (20 being the base-2 log of 1M), i.e. it really does reduce O(n log n) to O(n) in the mostly-sorted case. It's still somewhat slower than glibc's Introsort for random input, but now considerably faster than glibc when the input is already sorted, or mostly sorted.
Diffstat (limited to 'src')
-rw-r--r--src/stdlib/qsort.c225
1 files changed, 193 insertions, 32 deletions
diff --git a/src/stdlib/qsort.c b/src/stdlib/qsort.c
index 91a3361d..866af0ec 100644
--- a/src/stdlib/qsort.c
+++ b/src/stdlib/qsort.c
@@ -1,50 +1,211 @@
+/* Copyright (C) 2011 by Valentin Ochs
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+/* Minor changes by Rich Felker for integration in musl, 2011-04-27. */
+
+#include <stdint.h>
#include <stdlib.h>
#include <string.h>
-/* A simple heap sort implementation.. only in-place O(nlogn) sort I know. */
+#include "atomic.h"
+#define ntz(x) a_ctz_l((x))
-#define MIN(a, b) ((a)<(b) ? (a) : (b))
+typedef int (*cmpfun)(const void *, const void *);
+
+static inline int pntz(size_t p[2]) {
+ int r = ntz(p[0] - 1);
+ if(r != 0 || (r = 8*sizeof(size_t) + ntz(p[1])) != 8*sizeof(size_t)) {
+ return r;
+ }
+ return 0;
+}
-static void swap(char *a, char *b, size_t len)
+static void cycle(size_t width, unsigned char* ar[], int n)
{
- char tmp[256];
+ unsigned char tmp[256];
size_t l;
- while (len) {
- l = MIN(sizeof tmp, len);
- memcpy(tmp, a, l);
- memcpy(a, b, l);
- memcpy(b, tmp, l);
- a += l;
- b += l;
- len -= l;
+ int i;
+
+ if(n < 2) {
+ return;
+ }
+
+ ar[n] = tmp;
+ while(width) {
+ l = sizeof(tmp) < width ? sizeof(tmp) : width;
+ memcpy(ar[n], ar[0], l);
+ for(i = 0; i < n; i++) {
+ memcpy(ar[i], ar[i + 1], l);
+ ar[i] += l;
+ }
+ width -= l;
+ }
+}
+
+/* shl() and shr() need n > 0 */
+static inline void shl(size_t p[2], int n)
+{
+ if(n >= 8 * sizeof(size_t)) {
+ n -= 8 * sizeof(size_t);
+ p[1] = p[0];
+ p[0] = 0;
+ }
+ p[1] <<= n;
+ p[1] |= p[0] >> (sizeof(size_t) * 8 - n);
+ p[0] <<= n;
+}
+
+static inline void shr(size_t p[2], int n)
+{
+ if(n >= 8 * sizeof(size_t)) {
+ n -= 8 * sizeof(size_t);
+ p[0] = p[1];
+ p[1] = 0;
}
+ p[0] >>= n;
+ p[0] |= p[1] << (sizeof(size_t) * 8 - n);
+ p[1] >>= n;
}
-static void sift(char *base, size_t root, size_t nel, size_t width, int (*cmp)(const void *, const void *))
+static void sift(unsigned char *head, size_t width, cmpfun cmp, int pshift, size_t lp[])
{
- size_t max;
+ unsigned char *rt, *lf;
+ unsigned char *ar[14 * sizeof(size_t) + 1];
+ int i = 1;
+
+ ar[0] = head;
+ while(pshift > 1) {
+ rt = head - width;
+ lf = head - width - lp[pshift - 2];
- while (2*root <= nel) {
- max = 2*root;
- if (max < nel && cmp(base+max*width, base+(max+1)*width) < 0)
- max++;
- if (max && cmp(base+root*width, base+max*width) < 0) {
- swap(base+root*width, base+max*width, width);
- root = max;
- } else break;
+ if((*cmp)(ar[0], lf) >= 0 && (*cmp)(ar[0], rt) >= 0) {
+ break;
+ }
+ if((*cmp)(lf, rt) >= 0) {
+ ar[i++] = lf;
+ head = lf;
+ pshift -= 1;
+ } else {
+ ar[i++] = rt;
+ head = rt;
+ pshift -= 2;
+ }
}
+ cycle(width, ar, i);
}
-void qsort(void *_base, size_t nel, size_t width, int (*cmp)(const void *, const void *))
+static void trinkle(unsigned char *head, size_t width, cmpfun cmp, size_t pp[2], int pshift, int trusty, size_t lp[])
{
- char *base = _base;
- size_t i;
-
- if (!nel) return;
- for (i=(nel+1)/2; i; i--)
- sift(base, i-1, nel-1, width, cmp);
- for (i=nel-1; i; i--) {
- swap(base, base+i*width, width);
- sift(base, 0, i-1, width, cmp);
+ unsigned char *stepson,
+ *rt, *lf;
+ size_t p[2];
+ unsigned char *ar[14 * sizeof(size_t) + 1];
+ int i = 1;
+ int trail;
+
+ p[0] = pp[0];
+ p[1] = pp[1];
+
+ ar[0] = head;
+ while(p[0] != 1 || p[1] != 0) {
+ stepson = head - lp[pshift];
+ if((*cmp)(stepson, ar[0]) <= 0) {
+ break;
+ }
+ if(!trusty && pshift > 1) {
+ rt = head - width;
+ lf = head - width - lp[pshift - 2];
+ if((*cmp)(rt, stepson) >= 0 || (*cmp)(lf, stepson) >= 0) {
+ break;
+ }
+ }
+
+ ar[i++] = stepson;
+ head = stepson;
+ trail = pntz(p);
+ shr(p, trail);
+ pshift += trail;
+ trusty = 0;
+ }
+ if(!trusty) {
+ cycle(width, ar, i);
+ sift(head, width, cmp, pshift, lp);
+ }
+}
+
+void qsort(void *base, size_t nel, size_t width, cmpfun cmp)
+{
+ size_t lp[12*sizeof(size_t)];
+ size_t i, size = width * nel;
+ unsigned char *head = base,
+ *high = head + size - width;
+ size_t p[2] = {1, 0};
+ int pshift = 1;
+ int trail;
+
+ /* Precompute Leonardo numbers, scaled by element width */
+ for(lp[0]=lp[1]=width, i=2; (lp[i]=lp[i-2]+lp[i-1]+width) < size; i++);
+
+ while(head < high) {
+ if((p[0] & 3) == 3) {
+ sift(head, width, cmp, pshift, lp);
+ shr(p, 2);
+ pshift += 2;
+ } else {
+ if(lp[pshift - 1] >= high - head) {
+ trinkle(head, width, cmp, p, pshift, 0, lp);
+ } else {
+ sift(head, width, cmp, pshift, lp);
+ }
+
+ if(pshift == 1) {
+ shl(p, 1);
+ pshift = 0;
+ } else {
+ shl(p, pshift - 1);
+ pshift = 1;
+ }
+ }
+
+ p[0] |= 1;
+ head += width;
+ }
+
+ trinkle(head, width, cmp, p, pshift, 0, lp);
+
+ while(pshift != 1 || p[0] != 1 || p[1] != 0) {
+ if(pshift <= 1) {
+ trail = pntz(p);
+ shr(p, trail);
+ pshift += trail;
+ } else {
+ shl(p, 2);
+ pshift -= 2;
+ p[0] ^= 7;
+ shr(p, 1);
+ trinkle(head - lp[pshift] - width, width, cmp, p, pshift + 1, 1, lp);
+ shl(p, 1);
+ p[0] |= 1;
+ trinkle(head - width, width, cmp, p, pshift, 1, lp);
+ }
+ head -= width;
}
}