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That's interesting, but there are reasons other than performance for wanting fix-width integer semantics.

Try coding this with GMP (or any arbitrary precision math):

#! perl -slw use strict; use Math::Int128 qw[int128 uint128]; my $ZERO = uint128( 0 ); my $ONE = uint128( 1 ); my $ALLONES = ~ $ZERO; my $MASK1 = $ALLONES / 3; my $MASK2 = $ALLONES / 15 * 3; my $MASK3 = $ALLONES / 255; my $MASK4 = $MASK3 * 15; sub bcount { my $v = shift; $v = $v - ( ( $v >> 1 ) & $MASK1 ); $v = ( $v & $MASK2 ) + ( ( $v >> 2 ) & $MASK2 ); $v = ( $v + ( $v >> 4 ) ) & $MASK4; my $c = ( $v * ( $MASK3 ) ) >> 120; return $c; } my $bits = uint128( 0 ); ## set every 3rd bit $bits |= $ONE << $_ for map $_*3+1, 0 .. 42; print $bits; ## count the bits (43) print bcount( $bits ); ## now invert them and count again. (85) print bcount( ~$bits ); __END__ c:\test>m128.pl 194447066811964836264785489961010406546 43 85

Note: I would have supplied a GMPz version, but I couldn't work out how to do it from the docs. There seem to be a million ways to initialise a number; a million ways to divide two numbers etc, But not so much when it comes to doing bitwise math.

Update: Here's my attempt at a GMP version of the above. Note that it doesn't just produce the wrong results, but it does so silently:

#! perl -slw use strict; use Math::GMPz; my $ZERO = Math::GMPz->new( 0 ); my $ONE = Math::GMPz->new( 1 ); my $ALLONES = ~ $ZERO; my $MASK1 = $ALLONES / 3; my $MASK2 = $ALLONES / 15 * 3; my $MASK3 = $ALLONES / 255; my $MASK4 = $MASK3 * 15; sub bcount { my $v = shift; $v = $v - ( ( $v >> 1 ) & $MASK1 ); $v = ( $v & $MASK2 ) + ( ( $v >> 2 ) & $MASK2 ); $v = ( $v + ( $v >> 4 ) ) & $MASK4; my $c = ( $v * ( $MASK3 ) ) >> 120; return $c; } my $bits = Math::GMPz->new( 0 ); ## set every 3rd bit $bits |= $ONE << $_ for map $_*3+1, 0 .. 42; print $bits; ## count the bits (43) print bcount( $bits ); ## now invert them and count again. (85) print bcount( ~$bits ); __END__ c:\test>gmpz-t.pl 194447066811964836264785489961010406546 0 0

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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In reply to Re^13: Module for 128-bit integer math? (updated) by BrowserUk
in thread Module for 128-bit integer math? by BrowserUk

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