Convert a binary number, represented as a string (e.g. '101010'), to its decimal equivalent using first principles.
Implement binary to decimal conversion. Given a binary input string, your program should produce a decimal output. The program should handle invalid inputs.
Decimal is a base-10 system.
A number 23 in base 10 notation can be understood as a linear combination of powers of 10:
So: 23 => 2*10^1 + 3*10^0 => 2*10 + 3*1 = 23 base 10
Binary is similar, but uses powers of 2 rather than powers of 10.
So: 101 => 1*2^2 + 0*2^1 + 1*2^0 => 1*4 + 0*2 + 1*1 => 4 + 1 => 5 base 10
.
Go to the root of your PHP exercise directory, which is <EXERCISM_WORKSPACE>/php
.
To find the Exercism workspace run
% exercism debug | grep Workspace
Get PHPUnit if you don't have it already.
% wget --no-check-certificate https://phar.phpunit.de/phpunit.phar
% chmod +x phpunit.phar
Execute the tests:
% ./phpunit.phar binary/binary_test.php
All of Computer Science http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
<?php
class BinaryTest extends PHPUnit\Framework\TestCase
{
public static function setUpBeforeClass() : void
{
require_once 'binary.php';
}
public function testItParsesBinary0ToDecimal0() : void
{
$this->assertEquals(0, parse_binary('0'));
}
public function testItParsesBinary1ToDecimal1() : void
{
$this->assertEquals(1, parse_binary('1'));
}
public function testItParsesDigits() : void
{
$this->assertEquals(2, parse_binary('10'));
$this->assertEquals(3, parse_binary('11'));
$this->assertEquals(4, parse_binary('100'));
$this->assertEquals(9, parse_binary('1001'));
}
public function testItParsesHundreds() : void
{
$this->assertEquals(128, parse_binary('10000000'));
$this->assertEquals(315, parse_binary('100111011'));
$this->assertEquals(800, parse_binary('1100100000'));
$this->assertEquals(999, parse_binary('1111100111'));
}
public function testItParsesMaxInt() : void
{
$this->assertEquals(
9223372036854775807,
parse_binary('111111111111111111111111111111111111111111111111111111111111111')
);
}
public function testItParsesValuesWithLeadingZeros() : void
{
$this->assertEquals(1, parse_binary('01'));
$this->assertEquals(2, parse_binary('0010'));
$this->assertEquals(3, parse_binary('00011'));
}
/**
* @dataProvider invalidValues
*/
public function testItOnlyAcceptsStringsContainingZerosAndOnes($value) : void
{
$this->expectException(InvalidArgumentException::class);
parse_binary($value);
}
public function invalidValues() : array
{
return [
['2'], ['12345'], ['a'], ['0abcdef'],
];
}
}
<?php
function parse_binary($binary)
{
$output = 0;
$binaryLength = strlen($binary);
for ($i = 0; $i < $binaryLength; $i ++) {
if (!is_numeric($binary[$i]) || $binary[$i] > 1) {
throw new InvalidArgumentException();
}
$exponent = $binaryLength - $i - 1;
$output = bcadd($output, bcmul($binary[$i], bcpow(2, $exponent)));
}
return (int) $output;
}
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