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the math isn't automatically module 2^128

Quite so ... I don't think the gmp library provides a way of enforcing fixed precision. Therefore "the overflow" doesn't get automatically discarded, and you would have to remove it yourself by doing a mod(2 ** 128):
#! perl -slw use strict; use Math::GMPz qw(:mpz); my $ZERO = Math::GMPz->new( 0 ); my $ONE = Math::GMPz->new( 1 ); my $MOD128 = Math::GMPz->new(1) << 128; my $ALLONES = $MOD128 - 1; my $MASK1 = $ALLONES / 3; my $MASK2 = $ALLONES / 15 * 3; my $MASK3 = $ALLONES / 255; my $MASK4 = $MASK3 * 15; 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 ); print bcount($ALLONES ^ $bits); 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 ) ) % $MOD128) >> 120; return $c; } __END__ C:\_64\pscrpt>perl buk1.pl 194447066811964836264785489961010406546 43 85
Not sure what to do with the ~ operator in Math::GMPz. Currently it just does a one's complement - which is not the right thing for your purposes.
I notice that Math::GMP doesn't overload the ~ operator ... perhaps Math::GMPz should do the same ?

Cheers,
Rob

In reply to Re^16: Module for 128-bit integer math? (updated) by syphilis
in thread Module for 128-bit integer math? by BrowserUk

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