Promoting floats to doubles?

[Jim Wilson]

Kean Johnston wrote:
> Is there a way I can instruct GCC to always promote floats?

In K&R C, floats are promoted to double.  In ISO C, they are not.

The main difference here is prototypes.  If you have an old-style 
function definition, and there is no prototype in scope, then it will be 
compiled with floats promoted to double.  If you have a function call, 
and there is no prototype in scope, or this is an unnamed stdarg 
argument, then a float will be promoted to double.

If there is a prototype, and the prototype specifies float, then the 
float will not be promoted to double.

It sounds like you have a prototype that disagrees with the function 
definition, in which case you should fix the prototype.

There are some hooks here, TARGET_PROMOTE_FUNCTION_ARGS, 
TARGET_PROMOTE_PROTOTYPES, TARGET_PROMOTE_FUNCTION_RETURN, but they are 
really only useful for promoting char/short/int types.  They won't work 
for promoting float to double.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com