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Re^2: Efficient bit-twiddling in Perl.

by Tux (Monsignor)
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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