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A leap year check in three instructions

(hueffner.de)
420 points gnabgib | 1 comments | 15 May 25 21:57 UTC | HN request time: 0.202s | source
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charcircuit ◴[16 May 25 02:37 UTC] No.44001358[source]▶
The original function is likely only going to be 3 instructions. xor, test, jne and only 1 of these is dependent on a previous instruction. In the "fast" version from the article there are 4 instructions with each depending on the previous instruction. I'm not surprised it lost in the benchmark.
replies(2): >>44002317 #>>44002904 #
Dylan16807 ◴[16 May 25 08:07 UTC] No.44002904[source]▶
A branch that triggers 3/4 of the time will not perform well.

Whether that matters comes down to how this function integrates into the rest of the program.

replies(1): >>44008210 #
1. charcircuit ◴[16 May 25 18:00 UTC] No.44008210[source]▶
I don't think the years tested will be random. I think practically it will see long strings of the same value.