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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.arch
Subject: Re: Calling conventions (particularly 32-bit ARM)
Date: Tue, 14 Jan 2025 15:05:52 +0100
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On 13/01/2025 23:40, Scott Lurndal wrote:
> mitchalsup@aol.com (MitchAlsup1) writes:
>> On Mon, 13 Jan 2025 21:53:55 +0000, Scott Lurndal wrote:
>>
>>> mitchalsup@aol.com (MitchAlsup1) writes:
>>>> On Mon, 13 Jan 2025 18:02:10 +0000, Thomas Koenig wrote:
>>>>
>>>>> MitchAlsup1 <mitchalsup@aol.com> schrieb:
>>>>>
>>>>>> errno is an atrocity all by itself; single handedly preventing
>>>>>> direct use of SIN(), COS(), TAN(), ATAN(), exp(), ln(), pow()
>>>>>> as instructions.
>>>>>
>>>>> Fortunately, the C standard does not require errno to be set
>>>>> for these functions.  Apple, for example, does not do so.
>>>>
>>>> Nor will I.
>>>
>>> POSIX does, however, require errno to be set conditionally
>>> based on an application global variable 'math_errhandling'.
>>
>> The functions mentioned have the property of taking x as
>> any IEEE 754 number (including NaNs, infinities, denorms)
>> and produce a IEEE 754 number {NaNs, infinities, norms,
>> denorms}.
>>
>> But if POSIX wants to spend as many cycles setting errno
>> as performing the calculation, that is for POSIX to decide.
> 
> POSIX leaves it up to the programmer to decide.  If the
> programmer desires EDOM or ERANGE, they set the
> appropriate bit in math_errhandling before calling the
> sin et alia functions.
> 

You know POSIX better than I do, but AFAIK "math_errhandling" is a fixed 
value set by the implementation, usually as a macro.  Certainly with a 
quick check with gcc on Linux, I could not set the bits in math_errhandling.