[PATCH v3][BZ #17787] Fix exponents in manual.

[Joseph Myers]

On Thu, 18 Jun 2015, Carlos O'Donell wrote:

> > The macro definitions should go in macros.texi, rather than being 
> > duplicated in each file using it.
> 
> It would also seem sensible to keep such macros near their uses,
> and move them to macros.texi only if globally useful or repeated
> more than some nominal number of times.
> 
> What if the macro was only used in one place? Would we still put
> it into macros.texi?

If it were only used in one source file, it might be reasonable to define 
it there, but this macro is used in three source files.

Another issue with this patch: where it has "-@twoexp{63}" replacing 
"@math{-2^63}", the minus sign being outside @math will make it a hyphen 
rather than a minus sign (use @minus{} instead).  And one typo, 
"-2@twoexp{63}" has a stray "2" in there (should be 
"@minus{}@twoexp{63}").

-- 
Joseph S. Myers
joseph@codesourcery.com