Long multiplication
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You are encouraged to solve this task according to the task description, using any language you may know.
In this task, explicitly implement long multiplication. This is one possible approach to arbitrary-precision integer algebra.
For output, display the result of 2^64 * 2^64. The decimal representation of 2^64 is:
18446744073709551616
The output of 2^64 * 2^64 is 2^128, and that is:
340282366920938463463374607431768211456
Perl
<lang perl>#!/usr/bin/perl -w use strict;
- This should probably be done in a loop rather than be recursive.
sub add_with_carry {
my $resultref = shift; my $addend = shift; my $addendpos = shift;
push @$resultref, (0) while (scalar @$resultref < $addendpos + 1); my $addend_result = $addend + $resultref->[$addendpos]; my @addend_digits = reverse split //, $addend_result; $resultref->[$addendpos] = shift @addend_digits;
my $carry_digit = shift @addend_digits; &add_with_carry($resultref, $carry_digit, $addendpos + 1) if( defined $carry_digit )
}
sub longhand_multiplication {
my @multiplicand = reverse split //, shift; my @multiplier = reverse split //, shift; my @result = (); my $multiplicand_offset = 0; foreach my $multiplicand_digit (@multiplicand) { my $multiplier_offset = $multiplicand_offset; foreach my $multiplier_digit (@multiplier) { my $multiplication_result = $multiplicand_digit * $multiplier_digit; my @result_digit_addend_list = reverse split //, $multiplication_result;
my $addend_offset = $multiplier_offset; foreach my $result_digit_addend (@result_digit_addend_list) { &add_with_carry(\@result, $result_digit_addend, $addend_offset++) }
++$multiplier_offset; }
++$multiplicand_offset; }
@result = reverse @result;
return join , @result;
}
my $sixtyfour = "18446744073709551616";
my $onetwentyeight = &longhand_multiplication($sixtyfour, $sixtyfour); print "$onetwentyeight\n";</lang>