Returning COMPLEX Data (Fortran Programming Guide)

Fortran Programming Guide

Returning COMPLEX Data

A Fortran function returning COMPLEX or DOUBLE COMPLEX is equivalent to a C function with an additional first argument that points to the return value in memory. The general pattern for the Fortran function and its corresponding C function is:

Fortran function	C function
`COMPLEX FUNCTION CF(a1, a2, ..., an)`	`cf_ ()return, a1, a2, ..., an` `struct { float r, i; } *;return`

Fortran function

C function

COMPLEX FUNCTION CF(a1, a2, ..., an)

cf_ ()return, a1, a2, ..., an

struct { float r, i; } *;return

Table 11-14 Function Returning COMPLEX Data


Fortran calls C	C calls Fortran
`COMPLEX U, V, RETCPX` `EXTERNAL RETCPX` `U = ( 7.0, -8.0)` `V = RETCPX(U)` `...` `------------------------------` `struct complex { float r, i; };` `void retcpx_( temp, w )` `struct complex temp, w;` `{` `temp->r = w->r + 1.0;` `temp->i = w->i + 1.0;` `return;` `}`	`struct complex { float r, i; };` `struct complex c1, c2;` `struct complex u=&c1, v=&c2;` `extern retfpx_();` `u -> r = 7.0;` `u -> i = -8.0;` `retfpx_( v, u );` `...` `------------------------------` `COMPLEX FUNCTION RETFPX(Z)` `COMPLEX Z` `RETFPX = Z + (1.0, 1.0)` `RETURN` `END`

In 64-bit environments and compiling with -xarch=v9, COMPLEX values are returned in floating-point registers: COMPLEX and DOUBLE COMPLEX in %f0 and %f1, and COMPLEX*32 in %f0, %f1, %f2, and %f3.