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Inspired by BrowserUK's 2nd algorithm but slightly faster, since it calls substr just once in exchange for an extra assignment:
sub emazep { my $s = shift; my $tmp; ( ($tmp = substr $s, $_-1, 2) eq '11' or $tmp eq '00' ) and return +for @_; return 1; }
Using exactly the same benchmark provided here by BrowserUK, it gives:
Rate ysth japhy matija buk2 buk1 emazep ysth 1966/s -- -17% -87% -89% -89% -91% japhy 2361/s 20% -- -84% -87% -87% -89% matija 14719/s 648% 523% -- -19% -20% -32% buk2 18088/s 820% 666% 23% -- -1% -17% buk1 18363/s 834% 678% 25% 2% -- -16% emazep 21753/s 1006% 821% 48% 20% 18% --

Update:

added esialb's (corrected) solution to the BrowserUK's benchamrk:
Rate ysth japhy matija esialb buk1 buk2 emazep ysth 1975/s -- -17% -87% -88% -89% -89% -91% japhy 2374/s 20% -- -84% -85% -87% -87% -89% matija 15000/s 659% 532% -- -8% -17% -18% -30% esialb 16299/s 725% 586% 9% -- -10% -11% -23% buk1 18156/s 819% 665% 21% 11% -- -1% -15% buk2 18277/s 825% 670% 22% 12% 1% -- -14% emazep 21295/s 978% 797% 42% 31% 17% 17% --

2nd Update:

I've been misleaded by the BrowserUK solution, which contains an error which also slowed down his sub (see here.) After the correction his sub proves to be the fastest (dani_l's very elegant solution also included in the benchmark):
Rate ysth japhy esialb matija buk1 dani_l emazep buk2* ysth 1845/s -- -22% -85% -87% -88% -89% -90% -91% japhy 2366/s 28% -- -81% -84% -84% -86% -87% -88% esialb 12530/s 579% 430% -- -14% -16% -28% -31% -38% matija 14566/s 689% 516% 16% -- -2% -16% -20% -28% buk1 14885/s 707% 529% 19% 2% -- -14% -18% -27% dani_l 17357/s 841% 634% 39% 19% 17% -- -5% -14% emazep 18181/s 885% 669% 45% 25% 22% 5% -- -10% buk2* 20275/s 999% 757% 62% 39% 36% 17% 12% --
buk2* is the buk2 sub as corrected by me here.

Cheers, Emanuele.

In reply to Re: fast bit twiddling by emazep
in thread fast bit twiddling by spurperl

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