Hello,
I have not considered __builtin_constant_p(), I tend to forget all
those built in GCC functions after several failed attempts to use some
of them. I have been turning around your idea last days.
In my opinion the biggest weakness of my first proposed code is the
obscure error message when the parameter passed is not a constant. It
should help to present a clearer error message when the parameter is
invalid. __builtin_constant_p() facilitates the testing but it does not
allow to stop the compilation process by itself, and #error directive
cannot be used in a macro expansion. The solution seems to use
__builtin_constant_p() to conditionally compile the assembler directive
'.error'. This way, when a non constant argument is entered the file
compiles ok but the assembler stops showing errors. When combined with
'.print' directive, and __FILE__ and __LINE__ symbols to clone an
ordinary error message to help IDEs identifying the source of the error
*.c file, the result looks pretty good. This method also allows to
perform additional range checking in the delay parameter.
__builtin_constant_p() behaves slightly different depending on the
optimization level selected. With -O0 'const' qualified variables are
not recognized as constant values, and with optimization enabled
'const' variables are seen as any other numerical constant. This
introduces a little asymmetry.
In a couple of days or so I will complete testings and doxygen comment
checking, to upload the new version to Savannah.
Best regards,
Carlos.
[...]
David Brown wrote:
Carlos Lamas wrote:
<snip>
Problem 2. The proposed solution is to check the constant parameter
passed
against an inline assembler constraint in an empty dummy asm()
instruction.
This also requires to transform the inline function in a macro.
Passing a
variable as the argument to the macro generates an error a bit
obfuscated.
<snip>
Hi Carlos,
I don't know if you've considered it, but the
__builtin_constant_p(exp) function might be a better way to check
for constant parameters:
http://gcc.gnu.org/onlinedocs/gcc-4.2.2/gcc/Other-Builtins.html
[...]
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