Pure PHP MD4 implementation

md4.php

<?php

function preProcess($message) {
    $message .= chr(128);
    while (((strlen($message) + 8) % 64) !== 0) {
        $message .= chr(0);
    }
    return $message;
}

function rotl($x, $n) {
    return ($x << $n) | ($x >> (32 - $n));
}

function f($x, $y, $z) {
    return ($x & $y) | (~$x & $z);
}

function g($x, $y, $z)
{
    return ($x & $y) | ($x & $z) | ($y & $z);
}

function h($x, $y, $z)
{
    return $x ^ $y ^ $z;
}

function md4_hash($message) {
    list($a, $b, $c, $d) = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476];
    $originalSize = strlen($message) * 8;
    $message = preProcess($message);
    $chunks = str_split($message, 64);
    foreach ($chunks as $chunk) {
        $words = str_split($chunk, 4);
        foreach ($words as $i => $chrs) {
            $chrs = str_split($chrs);
            $word = '';
            $chrs = array_reverse($chrs);
            foreach ($chrs as $chr) {
                $word .= sprintf('%08b', ord($chr));
            }
            $words[$i] = bindec($word);
        }
        if (count($words) < 64) {
            $words[] = 0x00000000ffffffff & $originalSize; 
            $words[] = 0xffffffff00000000 & $originalSize; 
        }
        list($aa, $bb, $cc, $dd) = [$a, $b, $c, $d];
        foreach ([0, 4, 8, 12] as $i) {
            $a = rotl($a + f($b, $c, $d) + $words[$i+0] & 0xffffffff, 3);
            $d = rotl($d + f($a, $b, $c) + $words[$i+1] & 0xffffffff, 7);
            $c = rotl($c + f($d, $a, $b) + $words[$i+2] & 0xffffffff, 11);
            $b = rotl($b + f($c, $d, $a) + $words[$i+3] & 0xffffffff, 19) ;
        }
        foreach ([0, 1, 2, 3] as $i) {
            $a = rotl($a + g($b, $c, $d) + $words[$i+0] + 0x5a827999 & 0xffffffff, 3);
            $d = rotl($d + g($a, $b, $c) + $words[$i+4] + 0x5a827999 & 0xffffffff, 5);
            $c = rotl($c + g($d, $a, $b) + $words[$i+8] + 0x5a827999 & 0xffffffff, 9);
            $b = rotl($b + g($c, $d, $a) + $words[$i+12] + 0x5a827999 & 0xffffffff, 13);
        }
        foreach ([0, 2, 1, 3] as $i) {
            $a = rotl($a + h($b, $c, $d) + $words[$i+0] + 0x6ed9eba1 & 0xffffffff, 3);
            $d = rotl($d + h($a, $b, $c) + $words[$i+8] + 0x6ed9eba1 & 0xffffffff, 9);
            $c = rotl($c + h($d, $a, $b) + $words[$i+4] + 0x6ed9eba1 & 0xffffffff, 11);
            $b = rotl($b + h($c, $d, $a) + $words[$i+12] + 0x6ed9eba1 & 0xffffffff, 15);
        }
        $a = $a + $aa & 0xffffffff;
        $b = $b + $bb & 0xffffffff;
        $c = $c + $cc & 0xffffffff;
        $d = $d + $dd & 0xffffffff;
    }
    $x = pack('V4', $a, $b, $c, $d);
    return bin2hex($x);
}

echo md4_hash('message digest'),PHP_EOL;
echo hash('md4', 'message digest'),PHP_EOL;