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.

1 files changed, 63 insertions, 22 deletions

diff --git a/src/lib/libc/stdlib/qsort.c b/src/lib/libc/stdlib/qsort.c
index 4fe54eb5ff..58f2ec4709 100644
--- a/src/lib/libc/stdlib/qsort.c
+++ b/src/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);