Posts by skewray@mathstodon.xyz
(DIR) Post #B4F1OJjCHFln45cWsC by skewray@mathstodon.xyz
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According to Wikipedia, the only modern processor with 128-bit IEEE floating point is the IBM POWER9. Out of curiosity, using my Intel desktop I did a floating point speed test in C (gcc no optimization) with a zillion [multiply and 2 adds] operations. These are the results, normalized to float:1 float1 double85 long double7.3 quad (__float128)Um. Looks like this processor has hardware quad and emulates 80287 10-byte long double in software?I am shocked. Shocked! Processor is 13th Gen Intel® Core™ i9-13900 (24-Core, 32MB Cache, 2.0 GHz).
(DIR) Post #B4F1OJxjPDObnAQ8Wm by skewray@mathstodon.xyz
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So, apparently this is what happens when the value overflows and the processor is dealing with 'inf' in the loop: long double is much slower with exceptions. With numbers and not exceptions, the results are (now multiply and single add):gcc -O0float 1.00double 1.00long 1.32quad 8.5125.605u 0.000s 0:25.60 100.0% 0+0k 0+0io 0pf+0wgcc -O1float 1.00double 0.90 long 1.23 quad 8.4925.521u 0.001s 0:25.52 100.0% 0+0k 0+8io 0pf+0wgcc -O2float 1.00 double 0.99 long 1.36 quad 8.75 24.135u 0.000s 0:24.13 100.0% 0+0k 0+0io 0pf+0wgcc -O3float 1.00double 1.00 long 1.38quad 8.8324.144u 0.000s 0:24.14 100.0% 0+0k 0+8io 0pf+0wOptimization makes little to no difference to speed, as expected.
(DIR) Post #B4F1OKEkNx0UdwNj3A by skewray@mathstodon.xyz
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Seems to be a compiler issue, and only long double when unoptimized.TYPE NUM NAN INFfloat 1.00 0.99 0.99double 0.99 0.99 0.99long 1.25 69.68 72.13quad 8.42 5.99 6.61369.205u 0.000s 6:09.22 99.9%0+0k 0+8io 0pf+0wgcc -O1float 1.00 0.14 0.14double 1.00 0.14 0.14long 1.00 0.14 0.14quad 13.96 0.15 0.1522.730u 0.000s 0:22.73 100.0%0+0k 0+0io 0pf+0wgcc -O2float 1.00 0.00 0.00double 0.98 0.00 0.00long 0.99 0.00 0.00quad 13.67 0.00 0.0021.258u 0.000s 0:21.25 100.0%0+0k 0+8io 0pf+0wgcc -O3float 1.00 0.00 0.00double 0.98 0.00 0.00long 0.98 0.00 0.00quad 13.53 0.00 0.0021.094u 0.000s 0:21.09 100.0%0+0k 0+0io 0pf+0w
(DIR) Post #B4F1OKULRxU3QJgBMW by skewray@mathstodon.xyz
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@AmenZwa @dougmerritt https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124434
(DIR) Post #B4F1OKvzn9bMo4cGSe by skewray@mathstodon.xyz
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@AmenZwa @dougmerritt The bug report already got rejected. Turns out that x87 emulation is nasty. There's a big discussion in the bug ticket.
(DIR) Post #B4F1OLLAHZjc48OMgy by skewray@mathstodon.xyz
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@dougmerritt @AmenZwa I'm not sure if gcc can fix it. If the x87 variables are loaded on the stack for debugging, (which is supposedly what the default of -O0 means), then unwinding the stack on fault is slow. At least, that's the story they are telling, and they've marked it 'invalid' rather than 'wontfix'. I bet gcc never marks anything 'wontfix'.The fundamental issue is that the x87 architecture belongs in a museum.
(DIR) Post #B4F1OLoaWBGpXO9rYO by skewray@mathstodon.xyz
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@dougmerritt @AmenZwa Yesterday I went for a walk through eBay offerings on POWER9. It would be pretty easy to put together a POWER9 (or maybe even Power10) computer, probably for about US$5K+. (Maybe if I win the lottery?) Otherwise, quad is about 7 times slower than long double, so if I need speed, I can just run code on all 32 Intel processors and I am still ahead.For the computations I was doing late last year, long double wasn't good enough anyway; I needed quad accuracy.("x87" refers to the x86 floating point co-processor, which used 80-bit floating point. Long double is 10 bytes long and stored in a 16-byte space with 4 zeroed-out bytes. Super-retro.)
(DIR) Post #B5M7VlqI9WkTv46xKC by skewray@mathstodon.xyz
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@grips I store my chlorine as equamolar solid with sodium. It's so safe this way, you can even eat it.
(DIR) Post #B5vmDH96RKFo9ko5Vw by skewray@mathstodon.xyz
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Neutrino detection technology demonstration satellite SNAPPY successfully launched this morning. Now, to communicate!https://www.skewray.com/articles/snappy-neutrino-detecting-satellite#neutrinos #heliophysics #spaceinstruments #physics
(DIR) Post #B6oS55XKsvwBoBVTkm by skewray@mathstodon.xyz
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@hn100 Related: https://en.wikipedia.org/wiki/Lysenkoism