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L1

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The assert function is not a built-in part of Perl. You will need to install the CPAN module Devel::Assert to use it.
$ sudo CPAN install Devel::Assert
Assertions1.pl
#!/usr/bin/env perl
use utf8;
use Carp::Assert;
use Utils;
use strict;
use warnings;

our $TEST_BASE = 0.9;

sub exponentiation {
	my ($base, $power_arg) = @_;
	::assert($power_arg >= 0);
	my $power = $power_arg;
	my $result = 1.0;
	while ($power > 0) {
		$result *= $base;
		--$power;
	}
	return $result;
}

MAIN:
{
	for (my $p = 10; $p >= -1; --$p) {
		print Utils::messageFormat("\{0:f\} ^ \{1:d\} = \{2:f\}", $TEST_BASE, $p, exponentiation($TEST_BASE, $p)), "\n";
	}
}
Output
$ perl Assertions1.pl Assertion '$powerArg >= 0' failed at Assertions1.pl line 12. main::exponentiation(0.9, -1) called at Assertions1.pl line 25 0.900000 ^ 10 = 0.348678 0.900000 ^ 9 = 0.387420 0.900000 ^ 8 = 0.430467 0.900000 ^ 7 = 0.478297 0.900000 ^ 6 = 0.531441 0.900000 ^ 5 = 0.590490 0.900000 ^ 4 = 0.656100 0.900000 ^ 3 = 0.729000 0.900000 ^ 2 = 0.810000 0.900000 ^ 1 = 0.900000 0.900000 ^ 0 = 1.000000
Assertions2.pl
#!/usr/bin/env perl
use utf8;
use Carp::Assert;
use Utils;
use strict;
use warnings;

our $TEST_BASE = 0.9;

sub exponentiation {
	my ($base, $power_arg) = @_;
	::assert($power_arg >= 0, "exponentiation() power must be non-negative, was " . $power_arg);
	my $power = $power_arg;
	my $result = 1.0;
	while ($power > 0) {
		$result *= $base;
		--$power;
	}
	return $result;
}

MAIN:
{
	for (my $p = 10; $p >= -1; --$p) {
		print Utils::messageFormat("\{0:f\} ^ \{1:d\} = \{2:f\}", $TEST_BASE, $p, exponentiation($TEST_BASE, $p)), "\n";
	}
}
Output
$ perl Assertions2.pl Assertion '$powerArg >= 0' failed at Assertions2.pl line 12. main::exponentiation(0.9, -1) called at Assertions2.pl line 25 0.900000 ^ 10 = 0.348678 0.900000 ^ 9 = 0.387420 0.900000 ^ 8 = 0.430467 0.900000 ^ 7 = 0.478297 0.900000 ^ 6 = 0.531441 0.900000 ^ 5 = 0.590490 0.900000 ^ 4 = 0.656100 0.900000 ^ 3 = 0.729000 0.900000 ^ 2 = 0.810000 0.900000 ^ 1 = 0.900000 0.900000 ^ 0 = 1.000000
Assertions3.pl
#!/usr/bin/env perl
use utf8;
use Carp::Assert;
use Utils;
use strict;
use warnings;

our $TEST_BASE = 0.9;

sub exponentiation {
	my ($base, $power_arg) = @_;
	::assert($power_arg >= 0, "exponentiation() power must be non-negative, was " . $power_arg);
	my $power = $power_arg;
	my $result = 1.0;
	while ($power > 0) {
		$result *= $base;
		--$power;
	}
# This line will make the result incorrect.
	$result = -$result;
# If power is odd and base is negative, then result should be negative.
# Otherwise result should be positive.
	::assert((Utils::bitwiseAnd32($power, 1)) == 1 && ($base < 0.0) ? $result < 0.0 : $result >= 0.0, "Postcondition Failed: Result is wrong sign");
	return $result;
}

MAIN:
{
	for (my $p = 10; $p >= -1; --$p) {
		print Utils::messageFormat("\{0:f\} ^ \{1:d\} = \{2:f\}", $TEST_BASE, $p, exponentiation($TEST_BASE, $p)), "\n";
	}
}
Output
$ perl Assertions3.pl Assertion 'Utils::bitwiseAnd32($power, 1) == 1 && $base < 0 ? $result < 0 : $result >= 0' failed at Assertions3.pl line 23. main::exponentiation(0.9, 10) called at Assertions3.pl line 30
perl

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