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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.
OPENBSD_6_2
millert 7 years ago
parent
commit
fe11de237e
1 changed files with 63 additions and 22 deletions
  1. +63
    -22
      src/lib/libc/stdlib/qsort.c

+ 63
- 22
src/lib/libc/stdlib/qsort.c View File

@ -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);

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