src/gmxlib/gmx_blas/idamax.c

   1 #include <math.h>
   2 #include "gmx_blas.h"
   3
   4 int
   5 F77_FUNC(idamax,IDAMAX)(int *n__,
   6                         double *dx,
   7                         int *incx__)
   8 {
   9   int i,ix,idxmax;
  10   double dmax,tmp;
  11
  12   int n    = *n__;
  13   int incx = *incx__;
  14
  15   if(n<1 || incx<=0)
  16     return -1;
  17
  18   if(n==1)
  19     return 1;
  20
  21   dmax = fabs(dx[0]);
  22   idxmax = 1;
  23
  24   if(incx==1) {
  25     for(i=1;i<n;i++) {
  26       tmp = fabs(dx[i]);
  27       if(tmp>dmax) {
  28         dmax = tmp;
  29         idxmax = i+1;
  30       }
  31     }
  32   } else {
  33     /* Non-unit increments */
  34     ix = incx; /* this is really 0 + an increment */
  35     for(i=1;i<n;i++,ix+=incx) {
  36       tmp = fabs(dx[ix]);
  37       if(tmp>dmax) {
  38         dmax = tmp;
  39         idxmax = ix+1;
  40       }
  41     }
  42   }
  43   return idxmax;
  44 }