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/******************************************************************/
/* qsort.c -- Non-Recursive ANSI Quicksort function */
/* */
/* Public domain by Raymond Gardner, Englewood CO February 1991 */
/* */
/* Usage: */
/* qsort(base, nbr_elements, width_bytes, compare_function); */
/* void *base; */
/* size_t nbr_elements, width_bytes; */
/* int (*compare_function)(const void *, const void *); */
/* */
/* Sorts an array starting at base, of length nbr_elements, each */
/* element of size width_bytes, ordered via compare_function, */
/* which is called as (*compare_function)(ptr_to_element1, */
/* ptr_to_element2) and returns < 0 if element1 < element2, */
/* 0 if element1 = element2, > 0 if element1 > element2. */
/* Most refinements are due to R. Sedgewick. See "Implementing */
/* Quicksort Programs", Comm. ACM, Oct. 1978, and Corrigendum, */
/* Comm. ACM, June 1979. */
/******************************************************************/
/* John E. Davis: modifed to use my coding style and made gcc warning
* clean. Also, the name changed to reflect the fact that the function
* carries state data.
*/
#include <stddef.h> /* for size_t definition */
/* prototypes */
extern void _SLqsort (void *, size_t, size_t,
int (*)(void *, void *, void *), void *);
static void swap_chars(char *, char *, size_t);
/*
* Compile with -DSWAP_INTS if your machine can access an int at an
* arbitrary location with reasonable efficiency. Some machines
* cannot access an int at an odd address at all, so be careful.
*/
#ifdef SWAP_INTS
static void swap_ints(char *, char *, size_t);
# define SWAP(a, b) (swap_func((char *)(a), (char *)(b), width))
#else
# define SWAP(a, b) (swap_chars((char *)(a), (char *)(b), size))
#endif
#define COMP(a, b, c) ((*comp)((void *)(a), (void *)(b), (c)))
#define T 7
/* subfiles of T or fewer elements will be sorted by a simple insertion sort.
* Note! T must be at least 3
*/
void _SLqsort(void *basep, size_t nelems, size_t size,
int (*comp)(void *, void *, void *), void *cd)
{
char *stack[40], **sp; /* stack and stack pointer */
char *i, *j, *limit; /* scan and limit pointers */
size_t thresh; /* size of T elements in bytes */
char *base; /* base pointer as char * */
#ifdef SWAP_INTS
size_t width; /* width of array element */
void (*swap_func)(char *, char *, size_t); /* swap func pointer*/
width = size; /* save size for swap routine */
swap_func = swap_chars; /* choose swap function */
if ( size % sizeof(int) == 0 )
{
/* size is multiple of ints */
width /= sizeof(int); /* set width in ints */
swap_func = swap_ints; /* use int swap function */
}
#endif
base = (char *)basep; /* set up char * base pointer */
thresh = T * size; /* init threshold */
sp = stack; /* init stack pointer */
limit = base + nelems * size;/* pointer past end of array */
while (1)
{
/* repeat until break... */
if (limit > base + thresh)
{
/* if more than T elements, swap base with middle */
SWAP((((limit-base)/size)/2)*size+base, base);
i = base + size; /* i scans left to right */
j = limit - size; /* j scans right to left */
if (COMP(i, j, cd) > 0) /* Sedgewick's */
SWAP(i, j); /* three-element sort */
if (COMP(base, j, cd) > 0)/* sets things up */
SWAP(base, j); /* so that */
if (COMP(i, base,cd ) > 0)/* *i <= *base <= *j */
SWAP(i, base); /* *base is pivot element */
while (1)
{
do
{
/* move i right until *i >= pivot */
i += size;
}
while (COMP(i, base, cd) < 0);
/* move j left until *j <= pivot */
do
{
j -= size;
}
while (COMP(j, base, cd) > 0);
/* if pointers crossed, break loop */
if (i > j) break;
SWAP(i, j); /* else swap elements, keep scanning*/
}
SWAP(base, j); /* move pivot into correct place */
if (j - base > limit - i)
{
/* if left subfile larger */
sp[0] = base; /* stack left subfile base */
sp[1] = j; /* and limit */
base = i; /* sort the right subfile */
}
else
{
/* else right subfile larger*/
sp[0] = i; /* stack right subfile base */
sp[1] = limit; /* and limit */
limit = j; /* sort the left subfile */
}
sp += 2; /* increment stack pointer */
}
else
{
/* else subfile is small, use insertion sort */
j = base;
i = j + size;
while (i < limit)
{
while (COMP(j, j + size, cd) > 0)
{
SWAP(j, j+size);
if (j == base)
break;
j -= size;
}
j = i;
i += size;
}
if (sp == stack) /* done */
break;
/* if any entries on stack */
sp -= 2; /* pop the base and limit */
base = sp[0];
limit = sp[1];
}
}
}
/*
** swap nbytes between a and b
*/
static void swap_chars(char *a, char *b, size_t nbytes)
{
char tmp;
do
{
tmp = *a; *a++ = *b; *b++ = tmp;
}
while ( --nbytes );
}
#ifdef SWAP_INTS
/*
** swap nints between a and b
*/
static void swap_ints(char *ap, char *bp, size_t nints)
{
int *a = (int *)ap, *b = (int *)bp;
int tmp;
do
{
tmp = *a; *a++ = *b; *b++ = tmp;
}
while ( --nints );
}
#endif
#ifdef TESTING
#include <stdio.h>
#include <math.h>
static int cmp_fun (void *a, void *b, void *c)
{
double x, y;
double *xp, *yp;
double *data;
data = (double *) c;
xp = data + *(unsigned int *)a;
yp = data + *(unsigned int *)b;
x = *xp;
y = *yp;
if (x > y) return 1; else if (x < y) return -1;
if (xp > yp) return 1;
if (xp == yp) return 0;
return -1;
}
#define ARRAY_SIZE 10000
int main (int argc, char **argv)
{
unsigned int i;
double x, dx;
unsigned int index_array [ARRAY_SIZE];
double double_array [ARRAY_SIZE];
x = 0.0;
dx = 6.28 / ARRAY_SIZE;
for (i = 0; i < ARRAY_SIZE; i++)
{
double_array [i] = sin(x);
index_array [i] = i;
x += dx;
}
_SLqsort ((void *) index_array, ARRAY_SIZE,
sizeof (unsigned int), cmp_fun, (void *) double_array);
if (argc > 1)
for (i = 0; i < ARRAY_SIZE; i++)
{
fprintf (stdout, "%f\t%f\n",
double_array[i], double_array[index_array[i]]);
}
return 0;
}
#endif
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