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
|
#include <sys/types.h>
#include <stdlib.h>
static void exch(char* base,size_t size,size_t a,size_t b) {
char* x=base+a*size;
char* y=base+b*size;
while (size) {
char z=*x;
*x=*y;
*y=z;
--size; ++x; ++y;
}
}
/* Quicksort with 3-way partitioning, ala Sedgewick */
/* Blame him for the scary variable names */
/* http://www.cs.princeton.edu/~rs/talks/QuicksortIsOptimal.pdf */
static void quicksort(char* base,size_t size,ssize_t l,ssize_t r,
int (*compar)(const void*,const void*)) {
ssize_t i=l-1, j=r, p=l-1, q=r, k;
char* v=base+r*size;
if (r<=l) return;
for (;;) {
while (++i != r && compar(base+i*size,v)<0) ;
while (compar(v,base+(--j)*size)<0) if (j == l) break;
if (i >= j) break;
exch(base,size,i,j);
if (compar(base+i*size,v)==0) exch(base,size,++p,i);
if (compar(v,base+j*size)==0) exch(base,size,j,--q);
}
exch(base,size,i,r); j = i-1; ++i;
for (k=l; k<p; k++, j--) exch(base,size,k,j);
for (k=r-1; k>q; k--, i++) exch(base,size,i,k);
quicksort(base,size,l,j,compar);
quicksort(base,size,i,r,compar);
}
void qsort(void* base,size_t nmemb,size_t size,int (*compar)(const void*,const void*)) {
/* check for integer overflows */
if (nmemb >= (((size_t)-1)>>1) ||
size >= (((size_t)-1)>>1)) return;
if (nmemb>1)
quicksort(base,size,0,nmemb-1,compar);
}
|
