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#include <stdio.h>
#include <stdlib.h>
/* sample compar function: int cmp(void *a,void *b){ return *(int *)a-*(int *)b; } */
/* This qsort function does a little trick:
* To reduce stackspace it iterates the larger interval instead of doing
* the recursion on both intervals.
* So stackspace is limited to 32*stack_for_1_iteration =
* 32*4*(4 arguments+1 returnaddress+11 stored registers) = 2048 Bytes,
* which is small enough for everybodys use.
* (And this is the worst case if you own 4GB and sort an array of chars.)
* Sparing the function calling overhead does improve performance, too.
*/
void qsort
(void *base,size_t nmemb,size_t size,int (*compar)(const void *,const void *))
{ char *base2=(char *)base;
size_t i,a,b,c;
while(nmemb>1)
{ a=0;
b=nmemb-1;
c=(a+b)/2; /* Middle element */
for(;;)
{ while((*compar)(&base2[size*c],&base2[size*a])>0)
a++; /* Look for one >= middle */
while((*compar)(&base2[size*c],&base2[size*b])<0)
b--; /* Look for one <= middle */
if(a>=b)
break; /* We found no pair */
for(i=0;i<size;i++) /* swap them */
{ char tmp=base2[size*a+i];
base2[size*a+i]=base2[size*b+i];
base2[size*b+i]=tmp; }
if(c==a) /* Keep track of middle element */
c=b;
else if(c==b)
c=a;
a++; /* These two are already sorted */
b--;
} /* a points to first element of right intervall now (b to last of left) */
b++;
if(b<nmemb-b) /* do recursion on smaller intervall and iteration on larger one */
{ qsort(base2,b,size,compar);
base2=&base2[size*b];
nmemb=nmemb-b; }
else
{ qsort(&base2[size*b],nmemb-b,size,compar);
nmemb=b; }
}
}
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