saxpy.f.html
来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 85 行
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SUBROUTINE <a name="SAXPY.1"></a><a href="saxpy.f.html#SAXPY.1">SAXPY</a>(N,SA,SX,INCX,SY,INCY)
<span class="comment">*</span><span class="comment"> .. Scalar Arguments ..
</span> REAL SA
INTEGER INCX,INCY,N
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment"> .. Array Arguments ..
</span> REAL SX(*),SY(*)
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> Purpose
</span><span class="comment">*</span><span class="comment"> =======
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> <a name="SAXPY.13"></a><a href="saxpy.f.html#SAXPY.1">SAXPY</a> constant times a vector plus a vector.
</span><span class="comment">*</span><span class="comment"> uses unrolled loop for increments equal to one.
</span><span class="comment">*</span><span class="comment"> jack dongarra, linpack, 3/11/78.
</span><span class="comment">*</span><span class="comment"> modified 12/3/93, array(1) declarations changed to array(*)
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> .. Local Scalars ..
</span> INTEGER I,IX,IY,M,MP1
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment"> .. Intrinsic Functions ..
</span> INTRINSIC MOD
<span class="comment">*</span><span class="comment"> ..
</span> IF (N.LE.0) RETURN
IF (SA.EQ.0.0) RETURN
IF (INCX.EQ.1 .AND. INCY.EQ.1) GO TO 20
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> code for unequal increments or equal increments
</span><span class="comment">*</span><span class="comment"> not equal to 1
</span><span class="comment">*</span><span class="comment">
</span> IX = 1
IY = 1
IF (INCX.LT.0) IX = (-N+1)*INCX + 1
IF (INCY.LT.0) IY = (-N+1)*INCY + 1
DO 10 I = 1,N
SY(IY) = SY(IY) + SA*SX(IX)
IX = IX + INCX
IY = IY + INCY
10 CONTINUE
RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> code for both increments equal to 1
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> clean-up loop
</span><span class="comment">*</span><span class="comment">
</span> 20 M = MOD(N,4)
IF (M.EQ.0) GO TO 40
DO 30 I = 1,M
SY(I) = SY(I) + SA*SX(I)
30 CONTINUE
IF (N.LT.4) RETURN
40 MP1 = M + 1
DO 50 I = MP1,N,4
SY(I) = SY(I) + SA*SX(I)
SY(I+1) = SY(I+1) + SA*SX(I+1)
SY(I+2) = SY(I+2) + SA*SX(I+2)
SY(I+3) = SY(I+3) + SA*SX(I+3)
50 CONTINUE
RETURN
END
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