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C/C++ Users Group Library 1996 July
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C-C++ Users Group Library July 1996.iso
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vol_100
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161_01
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qsortpro.c
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1985-08-28
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/* qsort - sort array a (dimension n) using quicksort
* based on Bentley, CACM April 84
* Comments use notation A[i], a (fictitious) array of things
* that are of size elt_size.
*/
#include "local.h"
/* swapfn - swap elt_size bytes a <--> b (internal routine)
*/
void swapfn(a, b, elt_size)
register char *a; /* pointer to one element of A */
register char *b; /* pointer to another element of A */
size_t elt_size; /* size of each element */
{
register size_t i;
char tmp;
LOOPDN(i, elt_size)
{
SWAP(*a, *b, tmp);
++a, ++b;
}
} /*
.PE
.PS 25
/* iqsort - internal quicksort routine */
void iqsort(p_lo, p_hi, elt_size, cmpfn)
char *p_lo; /* ptr to low element of (sub)array */
char *p_hi; /* ptr to high element of (sub)array */
size_t elt_size; /* size of each element */
int (*cmpfn)(); /* comparison function ptr */
{
char *p_mid; /* pointer to middle element */
register char *p_i; /* pointer to A[i] */
register char *p_lastlo; /* pointer to A[lastlo] */
if (p_hi <= p_lo) /* is partition trivial? */
return;
p_mid = p_lo + ((((p_hi - p_lo) / elt_size) / 2) * elt_size);
swapfn(p_lo, p_mid, elt_size); /* pick the middle element as pivot */
p_lastlo = p_lo;
for (p_i = p_lo + elt_size; p_i <= p_hi; p_i += elt_size)
{
if ((*cmpfn)(p_lo, p_i) > 0)
{
p_lastlo += elt_size;
swapfn(p_lastlo, p_i, elt_size);
}
}
swapfn(p_lo, p_lastlo, elt_size);
iqsort(p_lo, p_lastlo - elt_size, elt_size, cmpfn);
iqsort(p_lastlo + elt_size, p_hi, elt_size, cmpfn);
} /*
.PE
.PS 9
/* qsort - the callable entry point */
void qsort(a, n, size, pf)
data_ptr a; /* address of array A to be sorted */
size_t n; /* number of elements in A */
size_t size; /* size of each element */
int (*pf)(); /* comparison function ptr */
{
iqsort((data_ptr)a, (char *)a + (n-1) * size, size, pf);
} /*
.PE
.PS 14
/* qsortm - test the qsort function */
static int a[100] =
{
0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
20, 21, 22, 23, 24, 25, 26, 27, 28, 29,
30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
50, 51, 52, 53, 54, 55, 56, 57, 58, 59,
60, 61, 62, 63, 64, 65, 66, 67, 68, 69,
70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
80, 81, 82, 83, 84, 85, 86, 87, 88, 89,
90, 91, 92, 93, 94, 95, 96, 97, 98, 99,
}; /*
.PE
.PS 11
/* intcmp - compare two ints */
int intcmp(pi, pj)
register int *pi, *pj;
{
if (*pi < *pj)
return (-1);
else if (*pi == *pj)
return (0);
else
return (1);
} /*
.PE
.PS 10
/* qsortm (main) - run the test */
main(ac, av)
int ac;
char *av[];
{
int i;
for (i = 1; i <= 1000; ++i)
qsort((data_ptr)a, 100, sizeof(int), intcmp);
}