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Old January 22nd 15, 04:25 AM posted to
Yousuf Khan[_2_]
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Posts: 1,296
Default Transcendental floating point functions are now unfixably brokenon Intel processors

On 21/01/2015 7:27 PM, wrote:
Wow, you're still here. I haven't peeked at comp.chips in years,
maybe a decade. Is Keith / KRW still around? I haven't seen or
heard from him since he retired. I see John Corse is still around,

Yeah, I check into it from time to time. At least it's still on my
newsgroups list. After it's done filtering out all of the spam, I might
see one posting in 3 months here on average.

To be on-topic, it's interesting to see the transcendentals broken
on Intel. I'm looking into AMD's HSA, and though the math can be
double-precision, I'd heard that transcendentals were fudged
single-precision. I'd thought of Intel as the gold standard on
this, at least after the integer bruising was fixed.

I think these days the transcendentals are all emulated in software
anyhow, so the precision now depends on how bug-free the floating point
libraries are, not now bug-free the hardware microcode is. AMD64 has
gotten rid of the x87 floating point unit, it's completely replaced by
the SSE2 and higher system, so it's not an option to use the hardware
transcendentals, since trancendentals are not part of the SSE specs. All
higher level floating point functions are now carried out by software.
So in a sense, the RISC idea of keeping complex functions to minimum has
won out, at least in the floating point side of x86.

Yousuf Khan