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User:Bjacob/ArithmeticTimingDifferences (view source)
Revision as of 21:30, 20 June 2013
, 20 June 2013→Timing differences in equality comparisons
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Specifically: | Specifically: | ||
* Recent Intel CPUs tend to have abnormally slow comparisons with NaN. | * Recent Intel CPUs tend to have abnormally slow comparisons with NaN. Examples: [http://people.mozilla.org/~bjacob/ta/results/intel-core-i7-2860QM-2.5GHz-family-6-model-42-stepping-7-thinkpad-w520/ Core i7], [http://people.mozilla.org/~bjacob/ta/results/intel-core-2-2.66GHz-family-6-model-15-stepping-11-st3fan/ Core 2]. | ||
* Recent AMD CPUs, older Intel CPUs, and Intel Atom CPUs have abnormally fast comparisons with NaN. Examples: | * Recent AMD CPUs, older Intel CPUs, and Intel Atom CPUs have abnormally fast comparisons with NaN. Examples: [http://people.mozilla.org/~bjacob/ta/results/amd-fx-8150-family-21-model-1-stepping-2-benwa-bulldozer/ AMD FX], [http://people.mozilla.org/~bjacob/ta/results/amd-athlon-ii-x4-635-family-16-model-5-stepping-2-gkwong/ Athlon II], [http://people.mozilla.org/~bjacob/ta/results/intel-pentium-b940-2GHz-family-6-model-42-stepping-7-gerv/ Pentium B940], [http://people.mozilla.org/~bjacob/ta/results/intel-pentium-4-3.2GHz-family-15-model-3-stepping-3-tycho/ Pentium 4], [http://people.mozilla.org/~bjacob/ta/results/intel-pentium-d-3GHz-family-15-model-4-stepping-7-dell-dimension9150-gavin/ Pentium D], [http://people.mozilla.org/~bjacob/ta/results/intel-atom-d510-1.66GHz-family-6-model-28-stepping-10-jvehent/ Intel Atom]. | ||
* Some VIA CPUs have abnormally fast comparisons with NaN and Inf. See this VIA Nano. | * Some VIA CPUs have abnormally fast comparisons with NaN and Inf. See [http://people.mozilla.org/~bjacob/ta/results/via-nano-u2250-1.6GHz-family-6-model-15-stepping-3-jvehent/ this VIA Nano]. | ||
=== Some CPUs have surprising timing differences on 64-bit integer arithmetic using 32-bit integer arithmetic instructions, when DAZ is enabled === | === Some CPUs have surprising timing differences on 64-bit integer arithmetic using 32-bit integer arithmetic instructions, when DAZ is enabled === | ||