2) It removes the need for sub bcount()
That does miss the point, which was not what the bcount() sub did, but the way it did it.
The result of using bitwise math using arbitrary precision doesn't follow the fix-width integer semantics. Ie. the math isn't automatically module 2^128.
That means you get quite different results: #! perl -slw
use strict;
use Math::GMPz;
my $ZERO = Math::GMPz->new( 0 );
my $ONE = Math::GMPz->new( 1 );
#my $ALLONES = ~ $ZERO;
my $ALLONES = (Math::GMPz->new(1) << 128) - 1;
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
4019000903644796537894933644280473643
6698389137940470254461716813547458644
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
-
Are you posting in the right place? Check out Where do I post X? to know for sure.
-
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big>
<blockquote> <br /> <dd>
<dl> <dt> <em> <font>
<h1> <h2> <h3> <h4>
<h5> <h6> <hr /> <i>
<li> <nbsp> <ol> <p>
<small> <strike> <strong>
<sub> <sup> <table>
<td> <th> <tr> <tt>
<u> <ul>
-
Snippets of code should be wrapped in
<code> tags not
<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
intervention).
-
Want more info? How to link
or How to display code and escape characters
are good places to start.
|