115 lines
4.1 KiB
C
Executable file
115 lines
4.1 KiB
C
Executable file
/*
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This software is in the public domain, furnished "as is", without technical
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support, and with no warranty, express or implied, as to its usefulness for
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any purpose.
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ExtFtn.h
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Some fortran compilers mangle the external symbols so that they do not
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conflict with symbols from modules written in other languages. In order
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to link an executable that calls Fortran functions from a C function, the
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C function must reference the mangled name.
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This macro performs the following mangling operations on a Fortran function
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depending on the following compilation switches.
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-DFTN_PREPEND_UNDERSCORE (i.e. _ftnfunc)
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-DFTN_APPEND_UNDERSCORE(i.e. ftnfunc_)
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-DFTN_PREPEND_DOUBLESCORE (i.e. __ftnfunc)
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-DFTN_APPEND_DOUBLESCORE (i.e. ftnfunc__)
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If no switches are used, then no name mangling is done.
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All external fortran declarations should be replaced with a call to
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this macro:
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EXT_FTN (funcReturnValue, funcName, funcArgs)
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For example, the declaration:
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extern "C" void gridbarbs(const float* uudd, const float* vvff);
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becomes
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EXT_FTN (void, gridbarbs, (const float* uudd, const float* vvff))
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We know this is kind of ugly. Ideally, you would just replace
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extern "C" with EXT_FTN. Unfortunately, the C preprocessor won't
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allow that.
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-- implementation ---------------------------------------------------------
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This macro does two jobs. First task is to come up with a new
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external declaration with the mangled name, which is fairly trivial.
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The second task is to make sure all invocations of the function
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reference the mangled function name. This is not so trivial.
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If CPP allowed us to nest macros definitions, we could do something like this:
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#ifdef FTN_APPEND_UNDERSCORE
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#define EXT_FUN(rval,fn,args)\
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extern "C" rval fn ## _ args;\
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#define fn fn ## _
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#endif
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But the CPP is not that sophisticated. The alternative we came up with
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is to use a function pointer. The name of the pointer is the non-mangled
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function name, and it is initialized to point to the mangled function.
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This works but there is a few loose ends we had to tie down. The
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function pointer has to be file scope (static). If its global,
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it would be very easy to have duplicate symbols defined. It is
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possible that the declaration could be in a header file with lots
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of other Fortran declarations. If a module never references a
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declaration, GCC will spit out an unused variable warning for the
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function pointer that goes with the declaration. To get around
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that, we use the GCC builtin unused attribute. Not pretty, but
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does the trick.
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One final note. We originally intended the compiler switches to be more
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flexible where a prefix and a suffix string can be specified. Unfortunately,
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due to limitations of the CPP, we couldn't get that to work.
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*/
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#ifndef _ExtFtn_h
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#define _ExtFtn_h
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#ifdef __GNUC__
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#define __UNUSED __attribute__ ((unused))
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#else
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#define __UNUSED
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#endif
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#ifdef __cplusplus
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#define EXTERN_C extern "C"
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#else
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#define EXTERN_C extern
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#endif
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#define EXT_FTN__(funcReturnVal,funcName,funcArgs,pre,post)\
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EXTERN_C funcReturnVal pre ## funcName ## post funcArgs;\
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static funcReturnVal (*funcName) funcArgs __UNUSED=pre ## funcName ## post;
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#if defined (FTN_APPEND_UNDERSCORE)
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#define EXT_FTN(funcReturnVal,funcName,funcArgs)\
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EXT_FTN__(funcReturnVal,funcName,funcArgs, ,_)
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#define FTN_MANGLE(funcName) funcName ## _
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#elif defined (FTN_PREPEND_UNDERSCORE)
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#define EXT_FTN(funcReturnVal,funcName,funcArgs)\
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EXT_FTN__(funcReturnVal,funcName,funcArgs,_, )
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#define FTN_MANGLE(funcName) _ ## funcName
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#elif defined (FTN_PREPEND_DOUBLESCORE)
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#define EXT_FTN(funcReturnVal,funcName,funcArgs)\
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EXT_FTN__(funcReturnVal,funcName,funcArgs,__, )
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#define FTN_MANGLE(funcName) __ ## funcName
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#elif defined (FTN_APPEND_DOUBLESCORE)
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#define EXT_FTN(funcReturnVal,funcName,funcArgs)\
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EXT_FTN__(funcReturnVal,funcName,funcArgs, ,__)
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#define FTN_MANGLE(funcName) funcName ## __
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#else
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#define EXT_FTN(funcReturnVal,funcName,funcArgs)\
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EXTERN_C funcReturnVal funcName funcArgs;
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#define FTN_MANGLE(funcName) funcName
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#endif
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#endif
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