@steve @hikari Does the specific phrasing "Apple's more recent ARM cores" suggest that other ARM cores do not

@steve @mcc @hikari On x86, you can disable throwing actual exceptions on sNaNs. The MXCSR register has "sticky" bits that you can clear before a sequence, then check afterwards. If there were any sNaNs read or produced during the sequence, the "Invalid Operation" sticky bit will be set. I believe qNaNs do not set the sticky bits.

This is rather klunky to use, and relies on the language/library having support for reading/setting the MXCSR, but it can be done.

@steve @mcc @hikari Is the question, "does anyone use snans directly" or does using the fp control registers to make all nans signal count. because we do the latter (and I believe it's reasonably common). (granted, we then combine this with fast-math so it's all kinds of nightmare, but anyway)

@dotstdy @mcc @hikari "We unmask invalid and run under fast-math" is some sort of shortest compiler-writer horror story entry.

@dotstdy @mcc @hikari Yes, I would like several hundred ud2 instructions sprinkled randomly throughout my program. I will definitely not regret this.

@steve @mcc @hikari my favorite part is when people work hard to write explicit nan checks and handling, which then immediately get thrown away by the compiler. (this is all only in internal builds, at least, but it's a bit funny)

@dotstdy @mcc @hikari we went to some length to avoid this in Apple's math.h, so you get a fast inline test when __FINITE_MATH_ONLY__ == 0 and a mandatory function call if you turn on fast-math. This still can't catch everything.

@steve @mcc @hikari Another fun case is when you generate nans with fast math, but don't without. Feels very Congrats, You Played Yourself.

@dotstdy @steve @mcc @hikari
people seriously use fast math?!

@Doomed_Daniel @steve @mcc @hikari well probably associative-math would get most of the buck without so much of the bang, but where's the fun in that.

@dotstdy @Doomed_Daniel @mcc @hikari associative-math and no-signed-zeros generally get you most of the benefits