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Re: Transcendental floating point functions are now unfixably broken on Intel processors

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On Friday, October 10, 2014 at 6:58:43 AM UTC-4, Yousuf Khan wrote:
> " This error has tragically become un-fixable because of the 
> compatibility requirements from one generation to the next. The fix for 
> this problem was figured out quite a long time ago. In the excellent 
> paper The K5 transcendental functions by T. Lynch, A. Ahmed, M. Schulte, 
> T. Callaway, and R. Tisdale a technique is described for doing argument 
> reduction as if you had an infinitely precise value for pi. As far as I 
> know, the K5 is the only x86 family CPU that did sin/cos accurately. AMD 
> went back to being bit-for-bit compatibile with the old x87 behavior, 
> assumably because too many applications broke. Oddly enough, this is 
> fixed in Itanium.
> 
> What we do in the JVM on x86 is moderately obvious: we range check the 
> argument, and if it's outside the range [-pi/4, pi/4]we do the precise 
> range reduction by hand, and then call fsin.
> 
> So Java is accurate, but slower. I've never been a fan of "fast, but 
> wrong" when "wrong" is roughly random(). Benchmarks rarely test 
> accuracy. "double sin(double theta) { return 0; }" would be a great 
> benchmark-compatible implementation of sin(). For large values of theta, 
> 0 would be arguably more accurate since the absolute error is never 
> greater than 1. fsin/fcos can have absolute errors as large as 2 
> (correct answer=1; returned result=-1). "
> 
> https://blogs.oracle.com/jag/entry/transcendental_meditation

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, same-old-same-old.

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.

Oops.

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Transcendental floating point functions are now unfixably broken on Intel processors Yousuf Khan <bbbl67@spammenot.yahoo.com> - 2014-10-10 06:58 -0400
  Re: Transcendental floating point functions are now unfixably broken on Intel processors Mark F <mark53916@gmail.com> - 2014-10-10 09:52 -0400
  Re: Transcendental floating point functions are now unfixably broken on Intel processors depontius@gmail.com - 2015-01-21 16:27 -0800
    Re: Transcendental floating point functions are now unfixably broken on Intel processors Yousuf Khan <bbbl67@spammenot.yahoo.com> - 2015-01-21 23:25 -0500
    Re: Transcendental floating point functions are now unfixably broken on Intel processors krw@attt.bizz - 2015-01-22 18:57 -0500
      Re: Transcendental floating point functions are now unfixably broken on Intel processors Yousuf Khan <bbbl67@spammenot.yahoo.com> - 2015-01-24 13:44 -0500
        Re: Transcendental floating point functions are now unfixably broken on Intel processors krw@attt.bizz - 2015-01-24 17:43 -0500
          Re: Transcendental floating point functions are now unfixably broken on Intel processors Yousuf Khan <bbbl67@spammenot.yahoo.com> - 2015-01-27 14:11 -0500
            Re: Transcendental floating point functions are now unfixably broken on Intel processors krw@attt.bizz - 2015-01-27 18:42 -0500
              Re: Transcendental floating point functions are now unfixably broken on Intel processors Yousuf Khan <bbbl67@spammenot.yahoo.com> - 2015-01-27 21:23 -0500
                Re: Transcendental floating point functions are now unfixably broken on Intel processors krw@attt.bizz - 2015-01-28 20:13 -0500
                Re: Transcendental floating point functions are now unfixably broken on Intel processors Yousuf Khan <bbbl67@spammenot.yahoo.com> - 2015-01-29 08:20 -0500
                Re: Transcendental floating point functions are now unfixably broken on Intel processors krw@attt.bizz - 2015-01-29 20:47 -0500
                Re: Transcendental floating point functions are now unfixably broken on Intel processors Yousuf Khan <bbbl67@spammenot.yahoo.com> - 2015-01-31 02:06 -0500
                Re: Transcendental floating point functions are now unfixably broken on Intel processors krw@attt.bizz - 2015-01-31 19:22 -0500

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