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<H1><A NAME="SECTION03370000000000000000"></A>
<A NAME="7324"></A>
<BR>
Accessing SIDL Arrays From FORTRAN 77
</H1>
<P>
For FORTRAN 77, the difference in how you access normal SIDL arrays and
r-arrays is profound. Normal SIDL arrays are passed in as an
<TT>integer*8</TT>, and you either access them using an function API or
by converting the array data to a index into a known array. R-arrays
appear like normal FORTRAN 77 arrays, so there is a big incentive to
use r-arrays unless you cannot.
<P>
The client-side interface for the <TT>solve</TT> example introduced in
Section <A HREF="node60.html#ss:r-arrays">5.4</A> behaves as if it is a FORTRAN 77 function
with the following declarations:
<P>
<BR>
<PRE CLASS="verbatim"> subroutine num_Linsol_solve_f(self, A, x, b, m, n)
implicit none
C in num.Linsol self
integer*8 self
integer*4 m, n
C in rarray<double,2> A(m,n)
double precision A(0:m-1, 0:n-1)
C inout rarray<double> x(n)
double precision x(0:n-1)
C in rarray<double> b(m)
double precision b(0:m-1)
end
</PRE></td></tr></table></blockquote>
<P>
FORTRAN 77 programmers should note that the array indices go from 0 to
<TT>m</TT><SPAN CLASS="MATH"><IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img24.png"
ALT="$-1$"></SPAN> instead of the normal 1 to <TT>m</TT>. This is a concession
to the C and C++ programmers who have to deal with the fact that A is
stored in column-major order.
<P>
On the server-side, the interface for <TT>solve</TT> appears as follows:
<P>
<BR>
<PRE CLASS="verbatim"> subroutine num_Linsol_solve_fi(self, A, x, b, m, n)
implicit none
C in num.Linsol self
integer*8 self
C in int m
integer*4 m
C in int n
integer*4 n
C in rarray<double,2> A(m,n)
double precision A(0:m-1, 0:n-1)
C inout rarray<double> x(n)
double precision x(0:n-1)
C in rarray<double> b(m)
double precision b(0:m-1)
C DO-NOT-DELETE splicer.begin(num.Linsol.solve)
C Insert the implementation here...
C DO-NOT-DELETE splicer.end(num.Linsol.solve)
end
</PRE></td></tr></table></blockquote>
<P>
Note again that the array indices go from 0 to <TT>m</TT><SPAN CLASS="MATH"><IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img24.png"
ALT="$-1$"></SPAN>. The
implementation should avoid changing the data in <TT>in</TT>
parameters.
<P>
The remainder of this section is dedicated to how you access normal
SIDL arrays. The normal SIDL C function API is available from FORTRAN
77 to create, destroy and access array elements and meta-data. The
function name for FORTRAN has <TT>_f</TT> appended.
<P>
For SIDL types dcomplex, double, fcomplex , float, int and long,
SIDL provides a method to get direct access to the array elements.
For the other types, you must use the functional API to access array elements.
<P>
For type X, there is a FORTRAN 77 function called <TT>sidl_X__array_access_f</TT> to
provide a method to get direct access.
An example is given below. Of course, this will
not work if your FORTRAN 77 compiler does array bounds checking.
<P>
<BR>
<PRE CLASS="verbatim"> integer*4 lower(1), upper(1), stride(1), i, index(1)
integer*4 value, refindex, refarray(1), modval
integer*8 nextprime, tmp
lower(1) = 0
value = 0
upper(1) = len - 1
call sidl_int__array_create_f(1, lower, upper, retval)
call sidl_int__array_access_f(retval, refarray, lower,
$ upper, stride, refindex)
do i = 0, len - 1
tmp = value
value = nextprime(tmp)
modval = mod(i, 3)
if (modval .eq. 0) then
call sidl_int__array_set1_f(retval, i, value)
else
if (modval .eq. 1) then
index(1) = i
call sidl_int__array_set_f(retval, index, value)
else
C this is equivalent to the sidl_int__array_set_f(retval, index, value)
refarray(refindex + stride(1)*(i - lower(1))) =
$ value
endif
endif
enddo
</PRE></td></tr></table></blockquote>
<P>
To access a two dimensional array, the expression referring to element i, j is
<P>
<BR>
<PRE CLASS="verbatim"> refarray(refindex + stride(1) * (i - lower(1)) + stride(2) * (j - lower(2))
</PRE></td></tr></table></blockquote>
<P>
To access a three dimensional array, the expression referring to element i, j k is
<P>
<BR>
<PRE CLASS="verbatim"> refarray(refindex + stride(1) * (i - lower(1)) + stride(2) * (j - lower(2))
</PRE></td></tr></table></blockquote>
<P>
You can call things like LINPACK or BLAS if you want,
but you should check the stride to make sure the array
is packed as you need it to be.
<TT>stride(i)</TT> indicates the distance between elements in dimension <TT>i</TT>.
A value of 1 means elements are packed densely in dimension <TT>i</TT>.
Negative stride values are possible, and when an array is
a slice of another array, there may be no dimension with a stride of 1.
<P>
For a <TT><I CLASS="slanted">dcomplex</I></TT> array, the reference array should a FORTRAN array of
<TT>REAL*8</TT> instead of a FORTRAN array of double complex to avoid potential
alignment problems. For a <TT><I CLASS="slanted">fcomplex</I></TT> array, the reference array is a
<TT>COMPLEX*8</TT> because we don't anticipate an alignment problem in this
case.
<P>
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