=head1 NAME

Math::Decimal::FastPP - Fast pure-Perl decimal arithmetic

=head1 SYNOPSIS

	use Math::Decimal::FastPP;

	$a = dadd($a, "1.23");  # $a += 1.23
	$c = dmul($a, $b);      # $c = $a * $b
	$a = drhtz($a);         # Round half towards zero

=head1 DESCRIPTION

Math::Decimal::FastPP provides a few common decimal arithmetic functions written
in pure Perl.  The functions are of course slower than Perl's built-in binary
floating-point arithmetic, but they're faster than L<Math::BigFloat> and other
commonly used decimal arithmetic modules.

This module is currently less complete than Perl's built-in arithmetic and other
decimal arithmetic modules.  So far it only includes addition, multiplication,
and rounding functions.

=head1 FUNCTIONS

=over 4

=cut

use strict;
use warnings;

package Math::Decimal::FastPP;

use Exporter qw(import);
our @EXPORT = qw(dadd dmul drhtz drhfz);

our $VERSION = "0.001";

=item dadd()

	$c = dadd($a, $b);

Adds C<$a> and C<$b> and returns their sum.

=cut

sub dadd
{
	my ($ai, $af) = split("\\.", $_[0]);
	my ($bi, $bf) = split("\\.", $_[1]);
	$af ||= "";
	$bf ||= "";
	my $ae = length($af);
	my $be = length($bf);
	my $ce;
	if ($ae == $be) {
		$ce = $ae;
	} elsif ($ae < $be) {
		$af .= "0" x ($be - $ae);
		$ce = $be;
	} else {
		$bf .= "0" x ($ae - $be);
		$ce = $ae;
	}
	my $as = $ai . $af;
	my $bs = $bi . $bf;
	my $cs = $as + $bs;
	$cs = sprintf("%0${ce}i", $cs);
	# The substr() code is 400% faster than this regular expression code.
	#$cs =~ s/(.{$ce})$/.$1/;
	#return $cs;
	return substr($cs, 0, length($cs) - $ce) . "." .
		substr($cs, length($cs) - $ce);
}

=item dmul()

	$c = dmul($a, $b);

Multiplies C<$a> and C<$b> and returns their product.

=cut

sub dmul
{
	my ($ai, $af) = split("\\.", $_[0]);
	my ($bi, $bf) = split("\\.", $_[1]);
	$af ||= "";
	$bf ||= "";
	my $as = $ai . $af;
	my $ae = length($af);
	my $bs = $bi . $bf;
	my $be = length($bf);
	my $cs = $as * $bs;
	my $ce = $ae + $be;
	$cs = sprintf("%0${ce}i", $cs);
	# The substr() code is 400% faster than this regular expression code.
	#$cs =~ s/(.{$ce})$/.$1/;
	#return $cs;
	return substr($cs, 0, length($cs) - $ce) . "." .
		substr($cs, length($cs) - $ce);
}

=item drhtz()

	$a = drhtz($a, $p);

Rounds C<$a> with precision C<$p>.  Halves are rounded towards zero.  For
example:

	drhtz("23.5", 0);   # Returns "23."
	drhtz("2.35", 1);   # Returns "2.3"
	drhtz("-23.5", 0);  # Returns "-23."
	drhtz("-2.35", 1);  # Returns "-2.3"

C<$p> is a non-negative (i.e. zero or positive) integer representing the number
of significant digits right of the radix point.

=cut

sub drhtz
{
	my ($ai, $af, $ad) = $_[0] =~ m/^(.*)\.(.{$_[1]})(.*)$/ or return;
	my $as = $ai . $af;
	++$as if $ad > "5" . "0" x (length($ad) - 1);
	$as = sprintf("%0$_[1]i", $as);
	# The substr() code is 400% faster than this regular expression code.
	#$as =~ s/(.{$_[1]})$/.$1/;
	#return $cs;
	return substr($as, 0, length($as) - $_[1]) . "." .
		substr($as, length($as) - $_[1]);
}

=item drhfz()

	$a = drhfz($a, $p);

Rounds C<$a> with precision C<$p>.  Halves are rounded away from zero.  For
example:

	drhfz("23.5", 0);   # Returns "24."
	drhtz("2.35", 1);   # Returns "2.4"
	drhfz("-23.5", 0);  # Returns "-24."
	drhtz("-2.35", 1);  # Returns "-2.4"

C<$p> is a non-negative (i.e. zero or positive) integer representing the number
of significant digits right of the radix point.

=cut

sub drhfz
{
	my ($ai, $af, $ad) = $_[0] =~ m/^(.*)\.(.{$_[1]})(.*)$/ or return;
	my $as = $ai . $af;
	++$as if $ad >= "5" . "0" x (length($ad) - 1);
	$as = sprintf("%0$_[1]i", $as);
	# The substr() code is 400% faster than this regular expression code.
	#$as =~ s/(.{$_[1]})$/.$1/;
	#return $as;
	return substr($as, 0, length($as) - $_[1]) . "." .
		substr($as, length($as) - $_[1]);
}

1;

__END__

=back

=head1 CAVEATS

These arithmetic functions preserve all significant fractional digits, including
trailing zeroes.  They also don't always add a leading zero before the radix
point for numbers with absolute values less than one.  So the output numbers can
look "ugly", like ".123000".  This is only an issue if the numbers (which are
returned as strings) are concatenated into other strings or printed without
formatting.  If this is an issue in your code, use the outputs as numbers (e.g.
C<$c + 0>) or print with formatting (with C<printf>).

=head1 AUTHOR

Patrick McDermott <patrick.mcdermott@libiquity.com>

=head1 SEE ALSO

L<Math::BigFloat>, L<Math::Decimal>

=head1 COPYRIGHT

Copyright (C) 2017  Patrick McDermott

=head1 LICENSE

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

=cut