root / src / blas / dscal.f @ 5
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SUBROUTINE DSCAL(N,DA,DX,INCX) |
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* .. Scalar Arguments .. |
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DOUBLE PRECISION DA |
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INTEGER INCX,N |
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* .. |
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* .. Array Arguments .. |
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DOUBLE PRECISION DX(*) |
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* .. |
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* |
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* Purpose |
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* ======= |
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** |
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* scales a vector by a constant. |
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* uses unrolled loops for increment equal to one. |
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* jack dongarra, linpack, 3/11/78. |
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* modified 3/93 to return if incx .le. 0. |
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* modified 12/3/93, array(1) declarations changed to array(*) |
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* |
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* |
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* .. Local Scalars .. |
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INTEGER I,M,MP1,NINCX |
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* .. |
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* .. Intrinsic Functions .. |
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INTRINSIC MOD |
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* .. |
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IF (N.LE.0 .OR. INCX.LE.0) RETURN |
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IF (INCX.EQ.1) GO TO 20 |
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* |
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* code for increment not equal to 1 |
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* |
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NINCX = N*INCX |
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DO 10 I = 1,NINCX,INCX |
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DX(I) = DA*DX(I) |
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10 CONTINUE |
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RETURN |
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* |
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* code for increment equal to 1 |
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* |
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* |
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* clean-up loop |
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* |
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20 M = MOD(N,5) |
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IF (M.EQ.0) GO TO 40 |
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DO 30 I = 1,M |
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DX(I) = DA*DX(I) |
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30 CONTINUE |
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IF (N.LT.5) RETURN |
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40 MP1 = M + 1 |
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DO 50 I = MP1,N,5 |
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DX(I) = DA*DX(I) |
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DX(I+1) = DA*DX(I+1) |
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DX(I+2) = DA*DX(I+2) |
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DX(I+3) = DA*DX(I+3) |
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DX(I+4) = DA*DX(I+4) |
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50 CONTINUE |
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RETURN |
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END |