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#!/usr/bin/perl
#
# Task 2: "Ethiopian Multiplication
#
# You are given two positive numbers $A and $B.
#
# Write a script to demonstrate
# https://rosettacode.org/wiki/Ethiopian_multiplication
# using the given numbers.
# "
#
# My notes: clearly defined, once you follow the link and discover what Ethiopian Multiplication is:-)
# Exercise for the interested reader: why does the method work? It follows directly from how BINARY
# multiplication actually works.
#
use strict;
use warnings;
use Data::Dumper;
use Function::Parameters;
use feature 'say';
use Getopt::Long;
my $debug = 0;
die "Usage: ethiopian-multiplication [--debug] A B\n" unless
GetOptions( "debug" => \$debug ) &&
@ARGV==2;
my( $a, $b ) = @ARGV;
say ethiopian( $a, $b );
#
# my $m = ethiopian( $a, $b );
# Use Ethiopian Multiplication - the original Egyptian/Ethiopian/Russian
# form of multiplication using repeated doublings and halvings.
#
fun ethiopian( $a, $b )
{
my $r = 0;
while( $a >= 1 )
{
say "r:$r, a:$a, b:$b" if $debug;
$r += $b if $a % 2 == 1;
$a /= 2; $a = int($a);
$b *= 2;
}
say "r:$r, a:$a, b:$b" if $debug;
return $r;
}
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