Annotation of rpl/lapack/blas/daxpy.f, revision 1.7
1.1 bertrand 1: SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY)
2: * .. Scalar Arguments ..
3: DOUBLE PRECISION DA
4: INTEGER INCX,INCY,N
5: * ..
6: * .. Array Arguments ..
7: DOUBLE PRECISION DX(*),DY(*)
8: * ..
9: *
10: * Purpose
11: * =======
12: *
13: * DAXPY constant times a vector plus a vector.
14: * uses unrolled loops for increments equal to one.
15: *
16: * Further Details
17: * ===============
18: *
19: * jack dongarra, linpack, 3/11/78.
20: * modified 12/3/93, array(1) declarations changed to array(*)
21: *
22: * =====================================================================
23: *
24: * .. Local Scalars ..
25: INTEGER I,IX,IY,M,MP1
26: * ..
27: * .. Intrinsic Functions ..
28: INTRINSIC MOD
29: * ..
30: IF (N.LE.0) RETURN
31: IF (DA.EQ.0.0d0) RETURN
1.7 ! bertrand 32: IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
! 33: *
! 34: * code for both increments equal to 1
! 35: *
! 36: *
! 37: * clean-up loop
! 38: *
! 39: M = MOD(N,4)
! 40: IF (M.NE.0) THEN
! 41: DO I = 1,M
! 42: DY(I) = DY(I) + DA*DX(I)
! 43: END DO
! 44: END IF
! 45: IF (N.LT.4) RETURN
! 46: MP1 = M + 1
! 47: DO I = MP1,N,4
! 48: DY(I) = DY(I) + DA*DX(I)
! 49: DY(I+1) = DY(I+1) + DA*DX(I+1)
! 50: DY(I+2) = DY(I+2) + DA*DX(I+2)
! 51: DY(I+3) = DY(I+3) + DA*DX(I+3)
! 52: END DO
! 53: ELSE
1.1 bertrand 54: *
55: * code for unequal increments or equal increments
56: * not equal to 1
57: *
1.7 ! bertrand 58: IX = 1
! 59: IY = 1
! 60: IF (INCX.LT.0) IX = (-N+1)*INCX + 1
! 61: IF (INCY.LT.0) IY = (-N+1)*INCY + 1
! 62: DO I = 1,N
1.1 bertrand 63: DY(IY) = DY(IY) + DA*DX(IX)
64: IX = IX + INCX
65: IY = IY + INCY
1.7 ! bertrand 66: END DO
! 67: END IF
1.1 bertrand 68: RETURN
69: END
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