Constants and -ffast-math

[David Ronis <ronis@ronispc.chem.mcgill.ca>]

I'm not sure that gcc is really my problem, but I have some messy
floating point code that isn't working.  Some debugging sessions have
started me thinking that perhaps I'm getting into trouble with
round-off error.

I have all floating-point's declared as doubles, except for explicit
floating point constants (like 1.0 or 0.0).

I was under the impression that 1.0 defaults to a double; does this
change with --fast-math?  It shouldn't, but I'm running out of ideas.

As long as I'm at it, could someone amplify on what exactly
--fast-math does, beyond the information in the gcc info docs.

Thanks

David