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1st ready version

#include "nrutil.h"
#define SWAP(a,b) temp=(a);(a)=(b);(b)=temp;
#define M 7
#define NSTACK 50

int sort(unsigned long n,float *arr)
{
	unsigned long i,ir=n,j,k,l=1,*istack;
	int jstack=0;
	float a,temp;
	int status=0;
	istack=lvector(1,NSTACK,&status);
	if (status<0) return(-1);
	for (;;) {
		if (ir-l < M) {
			for (j=l+1;j<=ir;j++) {
				a=arr[j];
				for (i=j-1;i>=l;i--) {
					if (arr[i] <= a) break;
					arr[i+1]=arr[i];
				}
				arr[i+1]=a;
			}
			if (jstack == 0) break;
			ir=istack[jstack--];
			l=istack[jstack--];
		} else {
			k=(l+ir) >> 1;
			SWAP(arr[k],arr[l+1])
			if (arr[l] > arr[ir]) {
				SWAP(arr[l],arr[ir])
			}
			if (arr[l+1] > arr[ir]) {
				SWAP(arr[l+1],arr[ir])
			}
			if (arr[l] > arr[l+1]) {
				SWAP(arr[l],arr[l+1])
			}
			i=l+1;
			j=ir;
			a=arr[l+1];
			for (;;) {
				do i++; while (arr[i] < a);
				do j--; while (arr[j] > a);
				if (j < i) break;
				SWAP(arr[i],arr[j]);
			}
			arr[l+1]=arr[j];
			arr[j]=a;
			jstack += 2;
			if (jstack > NSTACK) {
				//nrerror("NSTACK too small in sort.");
				return -1;
			}
			if (ir-i+1 >= j-l) {
				istack[jstack]=ir;
				istack[jstack-1]=i;
				ir=j-1;
			} else {
				istack[jstack]=j-1;
				istack[jstack-1]=l;
				l=i;
			}
		}
	}
	free_lvector(istack,1,NSTACK);
	return 0;
}
#undef M
#undef NSTACK
#undef SWAP