--- /dev/null
+#include "clapack.h"
+
+/* Subroutine */ int dswap_(integer *n, doublereal *dx, integer *incx,
+ doublereal *dy, integer *incy)
+{
+ /* System generated locals */
+ integer i__1;
+
+ /* Local variables */
+ integer i__, m, ix, iy, mp1;
+ doublereal dtemp;
+
+/* .. Scalar Arguments .. */
+/* .. */
+/* .. Array Arguments .. */
+/* .. */
+
+/* Purpose */
+/* ======= */
+
+/* interchanges two vectors. */
+/* uses unrolled loops for increments equal one. */
+/* jack dongarra, linpack, 3/11/78. */
+/* modified 12/3/93, array(1) declarations changed to array(*) */
+
+
+/* .. Local Scalars .. */
+/* .. */
+/* .. Intrinsic Functions .. */
+/* .. */
+ /* Parameter adjustments */
+ --dy;
+ --dx;
+
+ /* Function Body */
+ if (*n <= 0) {
+ return 0;
+ }
+ if (*incx == 1 && *incy == 1) {
+ goto L20;
+ }
+
+/* code for unequal increments or equal increments not equal */
+/* to 1 */
+
+ ix = 1;
+ iy = 1;
+ if (*incx < 0) {
+ ix = (-(*n) + 1) * *incx + 1;
+ }
+ if (*incy < 0) {
+ iy = (-(*n) + 1) * *incy + 1;
+ }
+ i__1 = *n;
+ for (i__ = 1; i__ <= i__1; ++i__) {
+ dtemp = dx[ix];
+ dx[ix] = dy[iy];
+ dy[iy] = dtemp;
+ ix += *incx;
+ iy += *incy;
+/* L10: */
+ }
+ return 0;
+
+/* code for both increments equal to 1 */
+
+
+/* clean-up loop */
+
+L20:
+ m = *n % 3;
+ if (m == 0) {
+ goto L40;
+ }
+ i__1 = m;
+ for (i__ = 1; i__ <= i__1; ++i__) {
+ dtemp = dx[i__];
+ dx[i__] = dy[i__];
+ dy[i__] = dtemp;
+/* L30: */
+ }
+ if (*n < 3) {
+ return 0;
+ }
+L40:
+ mp1 = m + 1;
+ i__1 = *n;
+ for (i__ = mp1; i__ <= i__1; i__ += 3) {
+ dtemp = dx[i__];
+ dx[i__] = dy[i__];
+ dy[i__] = dtemp;
+ dtemp = dx[i__ + 1];
+ dx[i__ + 1] = dy[i__ + 1];
+ dy[i__ + 1] = dtemp;
+ dtemp = dx[i__ + 2];
+ dx[i__ + 2] = dy[i__ + 2];
+ dy[i__ + 2] = dtemp;
+/* L50: */
+ }
+ return 0;
+} /* dswap_ */