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