73 lines
1.4 KiB
C
73 lines
1.4 KiB
C
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#include "nrutil.h"
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#define SWAP(a,b) itemp=(a);(a)=(b);(b)=itemp;
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#define M 7
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#define NSTACK 50
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void indexx(n,arr,indx)
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float arr[];
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unsigned long indx[],n;
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{
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unsigned long i,indxt,ir=n,itemp,j,k,l=1;
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int jstack=0,*istack;
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float a;
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istack=ivector(1,NSTACK);
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for (j=1;j<=n;j++) indx[j]=j;
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for (;;) {
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if (ir-l < M) {
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for (j=l+1;j<=ir;j++) {
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indxt=indx[j];
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a=arr[indxt];
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for (i=j-1;i>=l;i--) {
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if (arr[indx[i]] <= a) break;
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indx[i+1]=indx[i];
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}
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indx[i+1]=indxt;
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}
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if (jstack == 0) break;
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ir=istack[jstack--];
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l=istack[jstack--];
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} else {
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k=(l+ir) >> 1;
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SWAP(indx[k],indx[l+1]);
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if (arr[indx[l]] > arr[indx[ir]]) {
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SWAP(indx[l],indx[ir])
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}
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if (arr[indx[l+1]] > arr[indx[ir]]) {
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SWAP(indx[l+1],indx[ir])
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}
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if (arr[indx[l]] > arr[indx[l+1]]) {
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SWAP(indx[l],indx[l+1])
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}
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i=l+1;
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j=ir;
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indxt=indx[l+1];
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a=arr[indxt];
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for (;;) {
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do i++; while (arr[indx[i]] < a);
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do j--; while (arr[indx[j]] > a);
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if (j < i) break;
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SWAP(indx[i],indx[j])
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}
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indx[l+1]=indx[j];
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indx[j]=indxt;
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jstack += 2;
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if (jstack > NSTACK) nrerror("NSTACK too small in indexx.");
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if (ir-i+1 >= j-l) {
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istack[jstack]=ir;
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istack[jstack-1]=i;
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ir=j-1;
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} else {
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istack[jstack]=j-1;
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istack[jstack-1]=l;
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l=i;
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}
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}
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}
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free_ivector(istack,1,NSTACK);
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}
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#undef M
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#undef NSTACK
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#undef SWAP
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