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#!/usr/bin/perl
# Perl Weekly Challenge - 090
# - https://perlweeklychallenge.org/blog/perl-weekly-challenge-090/
#
# Task 2 Ethiopian Multiplication
#
# Author: Niels 'PerlBoy' van Dijke
use strict;
use warnings;
use List::Util qw(sum);
use Scalar::Util qw(looks_like_number);
# Unbuffered STDOUT
$|++;
@ARGV = (231, 13)
unless (@ARGV);
my ($M, $N) = @ARGV;
die "Please provide two integer numbers (x >= 0)"
unless (looks_like_number($M) and $M =~ m#^[1-9][0-9]*$# and
looks_like_number($N) and $N =~ m#^[1-9][0-9]*$#);
printf "%d x %d = %d\n", $M, $N, ethiopianMultiply($M,$N);
sub ethiopianMultiply {
my ($m, $n) = @_;
my $r;
while ($m) {
# Some nice binary operations (and & shift)
($r, $m, $n) = ($r += ($m & 1 ? $n : 0), $m >> 1, $n << 1);
}
return $r;
}
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