98 lines
1.9 KiB
C
98 lines
1.9 KiB
C
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#include "clapack.h"
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doublereal ddot_(integer *n, doublereal *dx, integer *incx, doublereal *dy,
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integer *incy)
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{
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/* System generated locals */
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integer i__1;
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doublereal ret_val;
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/* Local variables */
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integer i__, m, ix, iy, mp1;
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doublereal dtemp;
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/* .. Scalar Arguments .. */
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/* .. */
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/* .. Array Arguments .. */
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/* .. */
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/* Purpose */
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/* ======= */
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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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/* .. Local Scalars .. */
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/* .. */
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/* .. Intrinsic Functions .. */
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/* .. */
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/* Parameter adjustments */
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--dy;
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--dx;
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/* Function Body */
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ret_val = 0.;
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dtemp = 0.;
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if (*n <= 0) {
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return ret_val;
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}
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if (*incx == 1 && *incy == 1) {
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goto L20;
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}
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/* code for unequal increments or equal increments */
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/* not equal to 1 */
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ix = 1;
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iy = 1;
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if (*incx < 0) {
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ix = (-(*n) + 1) * *incx + 1;
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}
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if (*incy < 0) {
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iy = (-(*n) + 1) * *incy + 1;
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}
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i__1 = *n;
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for (i__ = 1; i__ <= i__1; ++i__) {
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dtemp += dx[ix] * dy[iy];
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ix += *incx;
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iy += *incy;
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/* L10: */
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}
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ret_val = dtemp;
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return ret_val;
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/* code for both increments equal to 1 */
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/* clean-up loop */
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L20:
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m = *n % 5;
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if (m == 0) {
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goto L40;
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}
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i__1 = m;
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for (i__ = 1; i__ <= i__1; ++i__) {
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dtemp += dx[i__] * dy[i__];
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/* L30: */
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}
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if (*n < 5) {
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goto L60;
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}
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L40:
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mp1 = m + 1;
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i__1 = *n;
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for (i__ = mp1; i__ <= i__1; i__ += 5) {
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dtemp = dtemp + dx[i__] * dy[i__] + dx[i__ + 1] * dy[i__ + 1] + dx[
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i__ + 2] * dy[i__ + 2] + dx[i__ + 3] * dy[i__ + 3] + dx[i__ +
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4] * dy[i__ + 4];
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/* L50: */
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}
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L60:
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ret_val = dtemp;
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return ret_val;
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} /* ddot_ */
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