On Thu, 2 Jul 2020, Vineet Gupta via Libc-alpha wrote:
> Now acos can come from 2 places depending on LIBM_SVID_COMPAT
> - math/w_acos_template.c <-- sets errno only
This wrapper, unlike the compat one, always calls __ieee754_acos
(appropriately suffixed), relying on it to raise appropriate exceptions.
The implementation in sysdeps/ieee754/dbl-64/e_asin.c raises the exception
by doing an Inf / Inf computation.
u.i[HIGH_HALF]=0x7ff00000;
v.i[HIGH_HALF]=0x7ff00000;
u.i[LOW_HALF]=0;
v.i[LOW_HALF]=0;
return u.x/v.x;
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95115
The right place to fix this is in GCC, to stop it constant-folding Inf /
Inf when flag_trapping_math. That should be a straightforward fix.
It would also be reasonable to change the above code to just "return 0.0 /
0.0;", as a simpler, more idiomatic way of returning a NaN with "invalid"
raised. (Any code constructing infinities / NaNs via bit patterns likely
predates built-in functions that can be used to represent such values
directly. Though the GCC bug means a literal replacement with "return
__builtin_inf () / __builtin_inf ();" wouldn't fix the present problem.)
--
Joseph S. Myers
jos...@codesourcery.com
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