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Transcendental floating point functions are now unfixably brokenon Intel processors
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/t...tal_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. |
Transcendental floating point functions are now unfixably brokenon Intel processors
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Transcendental floating point functions are now unfixably brokenon Intel processors
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Transcendental floating point functions are now unfixably broken on Intel processors
On Sat, 24 Jan 2015 13:44:23 -0500, Yousuf Khan
wrote: On 22/01/2015 6:57 PM, wrote: Hi Dale, I'm still "around" but there hasn't been much activity here for a decade or so. Oh, and I'm un-retired. Completely different industry, though. ...doing mostly analog design. ;-) These days there are other newsgroups that are more active on the PC front, such as: alt.comp.hardware.pc-homebuilt You guys should check it out, add it to your newsgroup list. The last PC I built was an original Opteron, if that tells you anything. ;-) |
Transcendental floating point functions are now unfixably brokenon Intel processors
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Transcendental floating point functions are now unfixably broken on Intel processors
On Tue, 27 Jan 2015 14:11:51 -0500, Yousuf Khan
wrote: On 24/01/2015 5:43 PM, wrote: On Sat, 24 Jan 2015 13:44:23 -0500, Yousuf Khan wrote: These days there are other newsgroups that are more active on the PC front, such as: alt.comp.hardware.pc-homebuilt You guys should check it out, add it to your newsgroup list. The last PC I built was an original Opteron, if that tells you anything. ;-) Well, if I trace back my current desktop, it can be trace it all of the way back to my first ever 8088 PC-XT clone. It's been upgraded continuously ever since, component by component. The difference is that my Opteron system has never been upgraded. It holds down the floor just as well as it did 12 years ago. It uses a lot less power, these days, though. |
Transcendental floating point functions are now unfixably brokenon Intel processors
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Transcendental floating point functions are now unfixably broken on Intel processors
On Tue, 27 Jan 2015 21:23:06 -0500, Yousuf Khan
wrote: On 27/01/2015 6:42 PM, wrote: On Tue, 27 Jan 2015 14:11:51 -0500, Yousuf Khan wrote: Well, if I trace back my current desktop, it can be trace it all of the way back to my first ever 8088 PC-XT clone. It's been upgraded continuously ever since, component by component. The difference is that my Opteron system has never been upgraded. It holds down the floor just as well as it did 12 years ago. It uses a lot less power, these days, though. Well, I still use my desktop daily, it's my most used computer. It's also scheduled for its next mini-upgrade in a few days or weeks. I'm going to be installing a water cooler to it, and then I'm going to be overclocking it. The current system is using a Phenom II X6 1100T, which is overclocking-ready. I did overclock it slightly back when I first got it, using its stock cooler. I did not really need the extra speed and decided to keep it at stock speed. I'm expecting that if I overclock it with water, I should be good with this current processor for another 2 years or so. I have *many* things that take up my time other than upgrading computers. I got out of that completely when I bought my first laptop. Computers have gotten boring. They're just another tool. |
Transcendental floating point functions are now unfixably brokenon Intel processors
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