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51 lines
1.2 KiB
C
51 lines
1.2 KiB
C
#include "blas.h"
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double ddot_(int *n, double *sx, int *incx, double *sy, int *incy)
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{
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long int i, m, nn, iincx, iincy;
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double stemp;
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long int ix, iy;
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/* forms the dot product of two vectors.
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uses unrolled loops for increments equal to one.
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jack dongarra, linpack, 3/11/78.
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modified 12/3/93, array(1) declarations changed to array(*) */
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/* Dereference inputs */
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nn = *n;
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iincx = *incx;
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iincy = *incy;
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stemp = 0.0;
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if (nn > 0)
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{
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if (iincx == 1 && iincy == 1) /* code for both increments equal to 1 */
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{
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m = nn-4;
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for (i = 0; i < m; i += 5)
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stemp += sx[i] * sy[i] + sx[i+1] * sy[i+1] + sx[i+2] * sy[i+2] +
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sx[i+3] * sy[i+3] + sx[i+4] * sy[i+4];
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for ( ; i < nn; i++) /* clean-up loop */
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stemp += sx[i] * sy[i];
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}
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else /* code for unequal increments or equal increments not equal to 1 */
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{
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ix = 0;
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iy = 0;
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if (iincx < 0)
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ix = (1 - nn) * iincx;
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if (iincy < 0)
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iy = (1 - nn) * iincy;
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for (i = 0; i < nn; i++)
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{
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stemp += sx[ix] * sy[iy];
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ix += iincx;
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iy += iincy;
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}
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}
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}
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return stemp;
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} /* ddot_ */
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