Re: [PATCHv2 3/5] ldbl-128: Rename 'long double' to '_Float128'

[Joseph Myers <joseph at codesourcery dot com>]

On Thu, 18 Aug 2016, Paul E. Murphy wrote:

> 	* sysdeps/ieee754/ldbl-128/math_ldbl.h:
> 	[!defined (FLT128_MANT_DIG)] (_Float128): Define as long double
> 	for compilers which do not support this type.

No, that's not the right condition.  For architectures where long double 
is binary128, with compilers that support _Float128, they are distinct 
types, and so _Float128 must be defined to long double (and constants 
likeiwse have long double type) so that functions whose type (declared in 
other headers) involves long double are also defined with the correct 
type.

So: if these files are being built for long double, regardless of whether 
_Float128 is supported, _Float128 must be a macro defined to long double 
so the functions get the correct type.  And if they are being built for 
_Float128, via wrappers in some other sysdeps directory, it's for files in 
that sysdeps directory to do whatever's needed to avoid the redefining of 
_Float128 as long double.

It's only in a context where the functions are defined directly with *f128 
names that you can avoid defining _Float128 to long double when the 
compiler supports _Float128 and they have the same format.  (In that 
context, you instead need to avoid the headers declaring the long double 
functions that will be aliased to the _Float128 ones, to avoid errors 
about the aliases having incompatible types.)

-- 
Joseph S. Myers
joseph@codesourcery.com