On Wed, 15 Nov 2017, Richard Biener wrote:
> Thanks - I suppose we can't avoid the repeated expansion by sth like
>
> #define exp(Val) ({ __typeof__ Val tem = Val; __TGMATH_UNARY_REAL_IMAG
> (tem, exp, cexp); })
Well, that still expands its argument twice. You'd need to use
__auto_type to avoid the double expansion. And then you'd still have
extremely complicated expansions (that are correspondingly unfriendly if a
user makes a mistake with a call, e.g. an argument of unsupported type),
and complications around getting the right semantics when decimal floating
point is involved. And use of ({ }) doesn't work in sizeof outside
functions. And that wouldn't help with cases such as
__STDC_TGMATH_OPERATOR_EVALUATION__, whereas it would actually be easy to
add __builtin_tgmath_operator that's handled the same as __builtin_tgmath
but ends up calling a function based on evaluation formats and producing
an EXCESS_PRECISION_EXPR.
(Clang overloadable functions in C don't avoid the multiple expansion
either, or at least Clang's tgmath.h doesn't.)
--
Joseph S. Myers
jos...@codesourcery.com
