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| 1 | SUBROUTINE DSWAP(N,DX,INCX,DY,INCY) |
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| 2 | * .. Scalar Arguments .. |
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| 3 | INTEGER INCX,INCY,N |
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| 4 | * .. |
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| 5 | * .. Array Arguments .. |
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| 6 | DOUBLE PRECISION DX(*),DY(*) |
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| 7 | * .. |
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| 8 | * |
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| 9 | * Purpose |
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| 10 | * ======= |
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| 11 | * |
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| 12 | * interchanges two vectors. |
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| 13 | * uses unrolled loops for increments equal one. |
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| 14 | * jack dongarra, linpack, 3/11/78. |
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| 15 | * modified 12/3/93, array(1) declarations changed to array(*) |
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| 16 | * |
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| 17 | * |
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| 18 | * .. Local Scalars .. |
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| 19 | DOUBLE PRECISION DTEMP |
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| 20 | INTEGER I,IX,IY,M,MP1 |
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| 21 | * .. |
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| 22 | * .. Intrinsic Functions .. |
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| 23 | INTRINSIC MOD |
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| 24 | * .. |
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| 25 | IF (N.LE.0) RETURN |
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| 26 | IF (INCX.EQ.1 .AND. INCY.EQ.1) GO TO 20 |
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| 27 | * |
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| 28 | * code for unequal increments or equal increments not equal |
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| 29 | * to 1 |
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| 30 | * |
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| 31 | IX = 1 |
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| 32 | IY = 1 |
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| 33 | IF (INCX.LT.0) IX = (-N+1)*INCX + 1 |
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| 34 | IF (INCY.LT.0) IY = (-N+1)*INCY + 1 |
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| 35 | DO 10 I = 1,N |
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| 36 | DTEMP = DX(IX) |
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| 37 | DX(IX) = DY(IY) |
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| 38 | DY(IY) = DTEMP |
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| 39 | IX = IX + INCX |
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| 40 | IY = IY + INCY |
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| 41 | 10 CONTINUE |
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| 42 | RETURN |
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| 43 | * |
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| 44 | * code for both increments equal to 1 |
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| 45 | * |
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| 46 | * |
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| 47 | * clean-up loop |
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| 48 | * |
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| 49 | 20 M = MOD(N,3) |
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| 50 | IF (M.EQ.0) GO TO 40 |
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| 51 | DO 30 I = 1,M |
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| 52 | DTEMP = DX(I) |
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| 53 | DX(I) = DY(I) |
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| 54 | DY(I) = DTEMP |
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| 55 | 30 CONTINUE |
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| 56 | IF (N.LT.3) RETURN |
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| 57 | 40 MP1 = M + 1 |
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| 58 | DO 50 I = MP1,N,3 |
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| 59 | DTEMP = DX(I) |
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| 60 | DX(I) = DY(I) |
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| 61 | DY(I) = DTEMP |
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| 62 | DTEMP = DX(I+1) |
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| 63 | DX(I+1) = DY(I+1) |
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| 64 | DY(I+1) = DTEMP |
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| 65 | DTEMP = DX(I+2) |
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| 66 | DX(I+2) = DY(I+2) |
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| 67 | DY(I+2) = DTEMP |
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| 68 | 50 CONTINUE |
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| 69 | RETURN |
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| 70 | END |
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