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authorTodd C. Miller <millert@cvs.openbsd.org>2017-05-24 21:18:26 +0000
committerTodd C. Miller <millert@cvs.openbsd.org>2017-05-24 21:18:26 +0000
commitc1dcab9d59d9dc1535945bc2b0589c645553d3a5 (patch)
tree79efb82fa2dff8caa812dedf1a92d3baf2b47ef7
parent1ebb93739edf01f5a7f5b37477ba3690fcbdee40 (diff)
Support swapping 32-bit aligned elements on 64-bit platforms.
Previously they would be swapped a byte at a time when sizeof(int) != sizeof(long). Idea from FreeBSD.
-rw-r--r--lib/libc/stdlib/qsort.c85
1 files changed, 63 insertions, 22 deletions
diff --git a/lib/libc/stdlib/qsort.c b/lib/libc/stdlib/qsort.c
index 4fe54eb5ff7..58f2ec47097 100644
--- a/lib/libc/stdlib/qsort.c
+++ b/lib/libc/stdlib/qsort.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: qsort.c,v 1.16 2017/05/20 12:48:56 millert Exp $ */
+/* $OpenBSD: qsort.c,v 1.17 2017/05/24 21:18:25 millert Exp $ */
/*-
* Copyright (c) 1992, 1993
* The Regents of the University of California. All rights reserved.
@@ -43,14 +43,26 @@ static __inline void swapfunc(char *, char *, size_t, int);
* 1. The partition value is swapped into a[0] instead of being
* stored out of line.
*
- * 2. It uses David Musser's introsort algorithm to fall back to
+ * 2. The swap function can swap 32-bit aligned elements on 64-bit
+ * platforms instead of swapping them as byte-aligned.
+ *
+ * 3. It uses David Musser's introsort algorithm to fall back to
* heapsort(3) when the recursion depth reaches 2*lg(n + 1).
* This avoids quicksort's quadratic behavior for pathological
* input without appreciably changing the average run time.
*
- * 3. Tail recursion is eliminated when sorting the larger of two
+ * 4. Tail recursion is eliminated when sorting the larger of two
* subpartitions to save stack space.
*/
+#define SWAPTYPE_BYTEV 1
+#define SWAPTYPE_INTV 2
+#define SWAPTYPE_LONGV 3
+#define SWAPTYPE_INT 4
+#define SWAPTYPE_LONG 5
+
+#define TYPE_ALIGNED(TYPE, a, es) \
+ (((char *)a - (char *)0) % sizeof(TYPE) == 0 && es % sizeof(TYPE) == 0)
+
#define swapcode(TYPE, parmi, parmj, n) { \
size_t i = (n) / sizeof (TYPE); \
TYPE *pi = (TYPE *) (parmi); \
@@ -62,25 +74,42 @@ static __inline void swapfunc(char *, char *, size_t, int);
} while (--i > 0); \
}
-#define SWAPINIT(a, es) swaptype = ((char *)a - (char *)0) % sizeof(long) || \
- es % sizeof(long) ? 2 : es == sizeof(long)? 0 : 1;
-
static __inline void
swapfunc(char *a, char *b, size_t n, int swaptype)
{
- if (swaptype <= 1)
- swapcode(long, a, b, n)
- else
- swapcode(char, a, b, n)
+ switch (swaptype) {
+ case SWAPTYPE_INT:
+ case SWAPTYPE_INTV:
+ swapcode(int, a, b, n);
+ break;
+ case SWAPTYPE_LONG:
+ case SWAPTYPE_LONGV:
+ swapcode(long, a, b, n);
+ break;
+ default:
+ swapcode(char, a, b, n);
+ break;
+ }
}
-#define swap(a, b) \
- if (swaptype == 0) { \
+#define swap(a, b) do { \
+ switch (swaptype) { \
+ case SWAPTYPE_INT: { \
+ int t = *(int *)(a); \
+ *(int *)(a) = *(int *)(b); \
+ *(int *)(b) = t; \
+ break; \
+ } \
+ case SWAPTYPE_LONG: { \
long t = *(long *)(a); \
*(long *)(a) = *(long *)(b); \
*(long *)(b) = t; \
- } else \
- swapfunc(a, b, es, swaptype)
+ break; \
+ } \
+ default: \
+ swapfunc(a, b, es, swaptype); \
+ } \
+} while (0)
#define vecswap(a, b, n) if ((n) > 0) swapfunc(a, b, n, swaptype)
@@ -93,11 +122,11 @@ med3(char *a, char *b, char *c, int (*cmp)(const void *, const void *))
}
static void
-introsort(char *a, size_t n, size_t es, size_t maxdepth,
+introsort(char *a, size_t n, size_t es, size_t maxdepth, int swaptype,
int (*cmp)(const void *, const void *))
{
char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
- int cmp_result, swaptype;
+ int cmp_result;
size_t r, s;
loop: if (maxdepth == 0) {
@@ -105,7 +134,6 @@ loop: if (maxdepth == 0) {
return;
}
maxdepth--;
- SWAPINIT(a, es);
if (n < 7) {
for (pm = a + es; pm < a + n * es; pm += es)
for (pl = pm; pl > a && cmp(pl - es, pl) > 0;
@@ -164,8 +192,10 @@ loop: if (maxdepth == 0) {
if (r < s) {
/* Recurse for 1st side, iterate for 2nd side. */
if (s > es) {
- if (r > es)
- introsort(a, r / es, es, maxdepth, cmp);
+ if (r > es) {
+ introsort(a, r / es, es, maxdepth,
+ swaptype, cmp);
+ }
a = pn - s;
n = s / es;
goto loop;
@@ -173,8 +203,10 @@ loop: if (maxdepth == 0) {
} else {
/* Recurse for 2nd side, iterate for 1st side. */
if (r > es) {
- if (s > es)
- introsort(pn - s, s / es, es, maxdepth, cmp);
+ if (s > es) {
+ introsort(pn - s, s / es, es, maxdepth,
+ swaptype, cmp);
+ }
n = r / es;
goto loop;
}
@@ -185,13 +217,22 @@ void
qsort(void *a, size_t n, size_t es, int (*cmp)(const void *, const void *))
{
size_t i, maxdepth = 0;
+ int swaptype;
/* Approximate 2*ceil(lg(n + 1)) */
for (i = n; i > 0; i >>= 1)
maxdepth++;
maxdepth *= 2;
- introsort(a, n, es, maxdepth, cmp);
+ if (TYPE_ALIGNED(long, a, es))
+ swaptype = es == sizeof(long) ? SWAPTYPE_LONG : SWAPTYPE_LONGV;
+ else if (sizeof(int) != sizeof(long) && TYPE_ALIGNED(int, a, es))
+ swaptype = es == sizeof(int) ? SWAPTYPE_INT : SWAPTYPE_INTV;
+ else
+ swaptype = SWAPTYPE_BYTEV;
+
+ introsort(a, n, es, maxdepth, swaptype, cmp);
+
}
DEF_STRONG(qsort);