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| From: | Paul Eggert |
| Subject: | Re: Missing _BitScanReverse64() |
| Date: | Mon, 05 Jan 2015 20:40:32 -0800 |
| User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 |
Pádraig Brady wrote:
I noticed that count_one_bits() branches on the popcount_support variable on each call, which might negate much of the gain from using this instruction?
Could be. As far as I know it's never been benchmarked. I stole that code from Emacs without investigating its performance (requires MS-Windows to test, which I don't have). It'd be nice to simplify the code by removing it if it doesn't help performance significantly on MS-Windows.
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