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Binary multiplication

by belg4mit (Prior)
on Mar 03, 2002 at 23:21 UTC ( [id://149032]=CUFP: print w/replies, xml ) Need Help??

I'm not sure if they teach you CS types this stuff in school but I read it long ago and recently come across it again, and I decided to implement the algorythm in perl for s&g.

It's called ethiopian multiplication. The premise is that peasants are not capable of performing multiplication proper but commerce has required them to implement a substitute.

#Division eq fractions eq multiplication... sub mul{ #If peasants can't multiply they certainly can't grok fractions use integer; my ($i, $j) = @_; my @results = ([$i, $j]); #Halve until we can halve no more while($i > 1){ my @z = ($i=halve($i), $j=double($j)); push @results, [@z]; } my $total; foreach( @results ){ #Even halves are evil $total += $_->[1] if $_->[0] % 2; } return $total; sub double{ #Cloning err doubling is easy; $_[0]+=$_[0]; } sub halve{ #Halving is a bit more tedious; my $count=0; while($_[0]>1){$_[0]-=2; $count++}; return $count; } }
And to think, it's almost 1/500_000th the speed of CORE multiplication. There are of course, overflow issues.

--
perl -pe "s/\b;([st])/'\1/mg"

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