Message 134428 - Python tracker

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In-reply-to
Author	vstinner
Recipients	jcea, mark.dickinson, rhettinger, vstinner
Date	2011年04月25日.23:43:47
SpamBayes Score	7.903878e-08
Marked as misclassified	No
Message-id	<1303775028.23.0.455371203888.issue11888@psf.upfronthosting.co.za>

Content
> Can't we simply use (approximation to 1/log(2)) * log(x)? > Is it worse than reimplementing it using log(x)/log(2) in Python? Hum. With a x86 and the right compiler optimization level, log(x)/log(2) in C can be more accurate than log(x)/log(2) in Python, because the FPU works with 80 bits float internally, and the result is only "truncated" to 64 bits float at the end. In Python, the result is truncated to 64 bits on each Python instruction. I don't know if it should be called a feature or a bug. In PHP world, it would be called a bug :-D http://bugs.php.net/bug.php?id=53632

Content

> Can't we simply use (approximation to 1/log(2)) * log(x)?
> Is it worse than reimplementing it using log(x)/log(2) in Python?
Hum. With a x86 and the right compiler optimization level, log(x)/log(2) in C can be more accurate than log(x)/log(2) in Python, because the FPU works with 80 bits float internally, and the result is only "truncated" to 64 bits float at the end. In Python, the result is truncated to 64 bits on each Python instruction.
I don't know if it should be called a feature or a bug. In PHP world, it would be called a bug :-D http://bugs.php.net/bug.php?id=53632

History
Date	User	Action	Args
2011年04月25日 23:43:48	vstinner	set	recipients: + vstinner, rhettinger, jcea, mark.dickinson
2011年04月25日 23:43:48	vstinner	set	messageid: <1303775028.23.0.455371203888.issue11888@psf.upfronthosting.co.za>
2011年04月25日 23:43:47	vstinner	link	issue11888 messages
2011年04月25日 23:43:47	vstinner	create

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