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Re^2: Efficient bit-twiddling in Perl.

by Tux (Abbot)
on Mar 01, 2013 at 14:16 UTC ( #1021270=note: print w/replies, xml ) Need Help??


in reply to Re: Efficient bit-twiddling in Perl.
in thread Efficient bit-twiddling in Perl.

When you reduce the overhead of the function calls (by doing the work you actually time in a tight loop), you might get other numbers

#!/pro/bin/perl -slw use 5.016; use warnings; use Benchmark qw{cmpthese :hireswallclock}; my $n = 0x80061861; say "and_rshift: $n => ", join (' : ', and_rshift ()); say "lshift_rshift: $n => ", join (' : ', lshift_rshift ()); say "mixed: $n => ", join (' : ', mixed ()); say "mixed_assign: $n => ", join (' : ', mixed_assign ()); say "just_shift: $n => ", join (' : ', just_shift ()); cmpthese (-10, { and_rshift => \&and_rshift, lshift_rshift => \&lshift_rshift, mixed => \&mixed, mixed_assign => \&mixed_assign, just_shift => \&just_shift, }); sub and_rshift { my ($top14, $nxt6, $mid6, $bot6); for (1..10000) { $top14 = ($n & 0xfffc0000) >> 18; $nxt6 = ($n & 0x0003f000) >> 12; $mid6 = ($n & 0x00000fc0) >> 6; $bot6 = ($n & 0x0000003f); } return ($top14, $nxt6, $mid6, $bot6); } sub lshift_rshift { my ($top14, $nxt6, $mid6, $bot6); for (1..10000) { $top14 = $n >> 18; $nxt6 = $n << 46 >> 58; $mid6 = $n << 52 >> 58; $bot6 = $n << 58 >> 58; } return ($top14, $nxt6, $mid6, $bot6); } sub mixed { my ($top14, $nxt6, $mid6, $bot6); for (1..10000) { ($top14, $nxt6, $mid6, $bot6) = ($n >> 18, $n >> 12 & 0x3f, $n >> 6 & 0x3f, $n & 0x3f); } return ($top14, $nxt6, $mid6, $bot6); } sub mixed_assign { my ($top14, $nxt6, $mid6, $bot6); for (1..10000) { $top14 = $n >> 18; $nxt6 = $n >> 12 & 0x3f; $mid6 = $n >> 6 & 0x3f; $bot6 = $n & 0x3f; } return ($top14, $nxt6, $mid6, $bot6); } sub just_shift { my ($top14, $nxt6, $mid6, $bot6); for (1..10000) { ($top14, $nxt6, $mid6, $bot6) = ($n >> 18, $n << 46 >> 58, $n << 52 >> 58, $n << 58 >> 58) +; } return ($top14, $nxt6, $mid6, $bot6); }
and_rshift: 2147883105 => 8193 : 33 : 33 : 33 lshift_rshift: 2147883105 => 8193 : 33 : 33 : 33 mixed: 2147883105 => 8193 : 33 : 33 : 33 mixed_assign: 2147883105 => 8193 : 33 : 33 : 33 just_shift: 2147883105 => 8193 : 33 : 33 : 33 Rate just_shift mixed mixed_assign and_rshift lsh +ift_rshift just_shift 247/s -- -2% -43% -48% + -52% mixed 252/s 2% -- -42% -47% + -52% mixed_assign 434/s 75% 72% -- -9% + -16% and_rshift 480/s 94% 90% 10% -- + -8% lshift_rshift 520/s 110% 106% 20% 8% + --

Enjoy, Have FUN! H.Merijn

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[marto]: "Eugenie Scott, executive director of the National Center for Science Education, dubbed this approach the Gish gallop, describing it as "where the creationist is allowed to run on for 45 minutes or an hour, spewing forth torrents of error that the
[marto]: evolutionist hasn't a prayer of refuting in the format of a debate." She also criticized Gish for failing to answer objections raised by his opponents"
[erix]: one would hope evolutionists haven't any prayers anyway
[marto]: obviously someone could be religious, but not creationist
[erix]: "Nothing in Intelligent Design makes sense except in the light of Creationism" <-- I made that one up myself (free after Dobzhansky )

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