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Annotation of rpl/lapack/blas/daxpy.f, revision 1.3

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
                     32:       IF (INCX.EQ.1 .AND. INCY.EQ.1) GO TO 20
                     33: *
                     34: *        code for unequal increments or equal increments
                     35: *          not equal to 1
                     36: *
                     37:       IX = 1
                     38:       IY = 1
                     39:       IF (INCX.LT.0) IX = (-N+1)*INCX + 1
                     40:       IF (INCY.LT.0) IY = (-N+1)*INCY + 1
                     41:       DO 10 I = 1,N
                     42:           DY(IY) = DY(IY) + DA*DX(IX)
                     43:           IX = IX + INCX
                     44:           IY = IY + INCY
                     45:    10 CONTINUE
                     46:       RETURN
                     47: *
                     48: *        code for both increments equal to 1
                     49: *
                     50: *
                     51: *        clean-up loop
                     52: *
                     53:    20 M = MOD(N,4)
                     54:       IF (M.EQ.0) GO TO 40
                     55:       DO 30 I = 1,M
                     56:           DY(I) = DY(I) + DA*DX(I)
                     57:    30 CONTINUE
                     58:       IF (N.LT.4) RETURN
                     59:    40 MP1 = M + 1
                     60:       DO 50 I = MP1,N,4
                     61:           DY(I) = DY(I) + DA*DX(I)
                     62:           DY(I+1) = DY(I+1) + DA*DX(I+1)
                     63:           DY(I+2) = DY(I+2) + DA*DX(I+2)
                     64:           DY(I+3) = DY(I+3) + DA*DX(I+3)
                     65:    50 CONTINUE
                     66:       RETURN
                     67:       END