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SUBROUTINE DSWAP (N,DX,INCX,DY,INCY) |
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C |
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C INTERCHANGES TWO VECTORS. |
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C USES UNROLLED LOOPS FOR INCREMENTS EQUAL ONE. |
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C JACK DONGARRA, LINPACK, 3/11/78. |
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C |
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DOUBLE PRECISION DX(*),DY(*),DTEMP |
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INTEGER I,INCX,INCY,IX,IY,M,MP1,N |
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C |
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IF(N.LE.0)RETURN |
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IF(INCX.EQ.1.AND.INCY.EQ.1)GO TO 20 |
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C |
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C CODE FOR UNEQUAL INCREMENTS OR EQUAL INCREMENTS NOT EQUAL |
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C TO 1 |
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C |
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IX = 1 |
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IY = 1 |
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IF(INCX.LT.0)IX = (-N+1)*INCX + 1 |
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IF(INCY.LT.0)IY = (-N+1)*INCY + 1 |
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DO 10 I = 1,N |
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DTEMP = DX(IX) |
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DX(IX) = DY(IY) |
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DY(IY) = DTEMP |
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IX = IX + INCX |
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IY = IY + INCY |
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10 CONTINUE |
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RETURN |
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C |
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C CODE FOR BOTH INCREMENTS EQUAL TO 1 |
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C |
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C |
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C CLEAN-UP LOOP |
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C |
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20 M = MOD(N,3) |
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IF( M .EQ. 0 ) GO TO 40 |
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DO 30 I = 1,M |
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DTEMP = DX(I) |
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DX(I) = DY(I) |
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DY(I) = DTEMP |
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30 CONTINUE |
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IF( N .LT. 3 ) RETURN |
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40 MP1 = M + 1 |
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DO 50 I = MP1,N,3 |
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DTEMP = DX(I) |
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DX(I) = DY(I) |
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DY(I) = DTEMP |
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DTEMP = DX(I + 1) |
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DX(I + 1) = DY(I + 1) |
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DY(I + 1) = DTEMP |
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DTEMP = DX(I + 2) |
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DX(I + 2) = DY(I + 2) |
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DY(I + 2) = DTEMP |
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50 CONTINUE |
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RETURN |
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END |
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