root / src / blas / ddot.f @ 1
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| 1 | 1 | equemene | DOUBLE PRECISION FUNCTION DDOT(N,DX,INCX,DY,INCY) |
|---|---|---|---|
| 2 | 1 | equemene | * .. Scalar Arguments .. |
| 3 | 1 | equemene | INTEGER INCX,INCY,N |
| 4 | 1 | equemene | * .. |
| 5 | 1 | equemene | * .. Array Arguments .. |
| 6 | 1 | equemene | DOUBLE PRECISION DX(*),DY(*) |
| 7 | 1 | equemene | * .. |
| 8 | 1 | equemene | * |
| 9 | 1 | equemene | * Purpose |
| 10 | 1 | equemene | * ======= |
| 11 | 1 | equemene | * |
| 12 | 1 | equemene | * forms the dot product of two vectors. |
| 13 | 1 | equemene | * uses unrolled loops for increments equal to one. |
| 14 | 1 | equemene | * jack dongarra, linpack, 3/11/78. |
| 15 | 1 | equemene | * modified 12/3/93, array(1) declarations changed to array(*) |
| 16 | 1 | equemene | * |
| 17 | 1 | equemene | * |
| 18 | 1 | equemene | * .. Local Scalars .. |
| 19 | 1 | equemene | DOUBLE PRECISION DTEMP |
| 20 | 1 | equemene | INTEGER I,IX,IY,M,MP1 |
| 21 | 1 | equemene | * .. |
| 22 | 1 | equemene | * .. Intrinsic Functions .. |
| 23 | 1 | equemene | INTRINSIC MOD |
| 24 | 1 | equemene | * .. |
| 25 | 1 | equemene | DDOT = 0.0d0 |
| 26 | 1 | equemene | DTEMP = 0.0d0 |
| 27 | 1 | equemene | IF (N.LE.0) RETURN |
| 28 | 1 | equemene | IF (INCX.EQ.1 .AND. INCY.EQ.1) GO TO 20 |
| 29 | 1 | equemene | * |
| 30 | 1 | equemene | * code for unequal increments or equal increments |
| 31 | 1 | equemene | * not equal to 1 |
| 32 | 1 | equemene | * |
| 33 | 1 | equemene | IX = 1 |
| 34 | 1 | equemene | IY = 1 |
| 35 | 1 | equemene | IF (INCX.LT.0) IX = (-N+1)*INCX + 1 |
| 36 | 1 | equemene | IF (INCY.LT.0) IY = (-N+1)*INCY + 1 |
| 37 | 1 | equemene | DO 10 I = 1,N |
| 38 | 1 | equemene | DTEMP = DTEMP + DX(IX)*DY(IY) |
| 39 | 1 | equemene | IX = IX + INCX |
| 40 | 1 | equemene | IY = IY + INCY |
| 41 | 1 | equemene | 10 CONTINUE |
| 42 | 1 | equemene | DDOT = DTEMP |
| 43 | 1 | equemene | RETURN |
| 44 | 1 | equemene | * |
| 45 | 1 | equemene | * code for both increments equal to 1 |
| 46 | 1 | equemene | * |
| 47 | 1 | equemene | * |
| 48 | 1 | equemene | * clean-up loop |
| 49 | 1 | equemene | * |
| 50 | 1 | equemene | 20 M = MOD(N,5) |
| 51 | 1 | equemene | IF (M.EQ.0) GO TO 40 |
| 52 | 1 | equemene | DO 30 I = 1,M |
| 53 | 1 | equemene | DTEMP = DTEMP + DX(I)*DY(I) |
| 54 | 1 | equemene | 30 CONTINUE |
| 55 | 1 | equemene | IF (N.LT.5) GO TO 60 |
| 56 | 1 | equemene | 40 MP1 = M + 1 |
| 57 | 1 | equemene | DO 50 I = MP1,N,5 |
| 58 | 1 | equemene | DTEMP = DTEMP + DX(I)*DY(I) + DX(I+1)*DY(I+1) + |
| 59 | 1 | equemene | + DX(I+2)*DY(I+2) + DX(I+3)*DY(I+3) + DX(I+4)*DY(I+4) |
| 60 | 1 | equemene | 50 CONTINUE |
| 61 | 1 | equemene | 60 DDOT = DTEMP |
| 62 | 1 | equemene | RETURN |
| 63 | 1 | equemene | END |