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1999-10-26  Andreas Jaeger  <aj@suse.de>

	* stdlib/msort.c: Include <alloca.h> for prototype.
	Remove K&R compatibility and _quicksort prototype.

	* stdlib/qsort.c: Make code and comments 64 bit clean; clarify
	some comments.
	Reported by Bernd Löchner <loechner@informatik.uni-kl.de>.
	Remove K&R compatibility.
	Move prototype declaration to include/stdlib.h.
	Include <alloca.h> for prototype; include <limits.h> for CHAR_BIT.

	* include/stdlib.h: Prototype declaration for _quicksort.
This commit is contained in:
Ulrich Drepper
1999-10-28 21:38:59 +00:00
parent 253d0b2377
commit 061d137bd7
4 changed files with 46 additions and 33 deletions
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37
stdlib/qsort.c
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@ -1,4 +1,4 @@
/* Copyright (C) 1991, 1992, 1996, 1997 Free Software Foundation, Inc.
/* Copyright (C) 1991, 1992, 1996, 1997, 1999 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Written by Douglas C. Schmidt (schmidt@ics.uci.edu).
@ -17,12 +17,15 @@
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
/* If you consider tuning this algorithm, you should consult first:
Engineering a sort function; Jon Bentley and M. Douglas McIlroy;
Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993. */
#include <alloca.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
extern void _quicksort __P ((void *const pbase, size_t total_elems,
size_t size, __compar_fn_t cmp));
/* Byte-wise swap two items of size SIZE. */
#define SWAP(a, b, size) \
do \
@ -49,7 +52,11 @@ typedef struct
} stack_node;
/* The next 4 #defines implement a very fast in-line stack abstraction. */
#define STACK_SIZE (8 * sizeof(unsigned long int))
/* The stack needs log (total_elements) entries (we could even subtract
log(MAX_THRESH)). Since total_elements has type size_t, we get as
upper bound for log (total_elements):
bits per byte (CHAR_BIT) * sizeof(size_t). */
#define STACK_SIZE (CHAR_BIT * sizeof(size_t))
#define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top))
#define POP(low, high) ((void) (--top, (low = top->lo), (high = top->hi)))
#define STACK_NOT_EMPTY (stack < top)
@ -60,9 +67,10 @@ typedef struct
1. Non-recursive, using an explicit stack of pointer that store the
next array partition to sort. To save time, this maximum amount
of space required to store an array of MAX_INT is allocated on the
stack. Assuming a 32-bit integer, this needs only 32 *
sizeof(stack_node) == 136 bits. Pretty cheap, actually.
of space required to store an array of SIZE_MAX is allocated on the
stack. Assuming a 32-bit (64 bit) integer for size_t, this needs
only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes).
Pretty cheap, actually.
2. Chose the pivot element using a median-of-three decision tree.
This reduces the probability of selecting a bad pivot value and
@ -75,15 +83,12 @@ typedef struct
4. The larger of the two sub-partitions is always pushed onto the
stack first, with the algorithm then concentrating on the
smaller partition. This *guarantees* no more than log (n)
smaller partition. This *guarantees* no more than log (total_elems)
stack size is needed (actually O(1) in this case)! */
void
_quicksort (pbase, total_elems, size, cmp)
void *const pbase;
size_t total_elems;
size_t size;
__compar_fn_t cmp;
_quicksort (void *const pbase, size_t total_elems, size_t size,
__compar_fn_t cmp)
{
register char *base_ptr = (char *) pbase;
@ -100,7 +105,6 @@ _quicksort (pbase, total_elems, size, cmp)
{
char *lo = base_ptr;
char *hi = &lo[size * (total_elems - 1)];
/* Largest size needed for 32-bit int!!! */
stack_node stack[STACK_SIZE];
stack_node *top = stack + 1;
@ -114,7 +118,8 @@ _quicksort (pbase, total_elems, size, cmp)
/* Select median value from among LO, MID, and HI. Rearrange
LO and HI so the three values are sorted. This lowers the
probability of picking a pathological pivot value and
skips a comparison for both the LEFT_PTR and RIGHT_PTR. */
skips a comparison for both the LEFT_PTR and RIGHT_PTR in
the while loops. */
char *mid = lo + size * ((hi - lo) / size >> 1);