[Hye-Shik Chang, reports on a particular sqrt implementation]
> ...
>> I'll submit PR to both of FreeBSD and NetBSD.
[Michael Hudson]
> I'm not sure it's a problem. I believe it depends on whether you
> believe in C89 or C99, for instance.
It's cute: even in C99, an implementation must treat sqrt(negative_number)
as a domain error. However, under C99 rules:
On a domain error, the function returns an implementation-defined
value; whether the integer expression errno acquires the value
EDOM is implementation-defined.
So while it's mandatory that an implementation detect that sqrt(-1) is a
domain error case, there's no x-platform way defined anymore for the library
to communciate the error condition to the caller.
That's why the exception test isn't run by default: C doesn't supply any
x-platform error facility Python can build on anymore. Python tries to
guess whether a range error occurred ("most of the time", C99 stilll
requires that HUGE_VAL specifically get returned then), but there's no way
to guess about domain errors short of Python hard-coding its own rules about
the proper domain on a function by function basis.
Do that, and in the end you get a library that still honks off IEEE-754 fans
anyway (which has its own elaborate and precise rules for dealing with fp
exceptions).
can't-win-without-more-work-than-anyone-will-give-it-ly y'rs - tim
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