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Branchless UTF-8 Encoding

(cceckman.com)
103 points vortex_ape | 1 comments | 17 Jan 25 19:20 UTC | HN request time: 0.224s | source
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xeeeeeeeeeeenu ◴[17 Jan 25 20:10 UTC] No.42742731[source]▶
> So on x86_64 processors, we have to branch to say “a 32-bit zero value has 32 leading zeros”.

Not if you're targeting x86-64-v3 or higher. Haswell (Intel) and Piledriver (AMD) introduced the LZCNT instruction that doesn't have this problem.

replies(2): >>42742835 #>>42742859 #
1. sltkr ◴[17 Jan 25 20:18 UTC] No.42742835[source]▶
You can also very trivially do (codepoint | 1).leading_zeros(), then you can also shave one byte off the LEN table. (This doesn't affect the result because LEN[32] == LEN[33] == 1).