Test genetic programming

testgp.php

<?php
$instructions = ['0', '1', '+', '-', '*', '/', '>', '<', '=', '|', '&', '@', '!', '#', '(', ')', '%', '_'];
$instructionsLength = count($instructions) - 1;

while (true) {
    $program = '';
    for ($i = 0, $c = rand(0, 10); $i < $c; $i++) {
        $program .= $instructions[rand(0, $instructionsLength)];
    }
    
    $resulta = vm([100], $program);
    $resultb = vm([25], $program);

    if ($resulta == [4] && $resultb == [4]) {
        echo 'Winning program: '.$program."\n";
        exit();
    }
}

function vm($inputs, $instructions) {
    $stack = $inputs;
    $hold = [];
    foreach (str_split($instructions) as $instruction) {
        switch ($instruction) {
            // Magic value
            case '0':
                array_unshift($stack, 0);
                break;
            // Magic value
            case '1':
                array_unshift($stack, 1);
                break;
            // Arithmetic addition
            case '+':
                if (empty($stack)) return;
                $a = array_shift($stack);
                if (empty($stack)) return;
                $b = array_shift($stack);
                array_unshift($stack, $a + $b);
                break;
            // Arithmetic substraction
            case '-':
                if (empty($stack)) return;
                $a = array_shift($stack);
                if (empty($stack)) return;
                $b = array_shift($stack);
                array_unshift($stack, $a - $b);
                break;
            // Arithmetic multiplication
            case '*':
                if (empty($stack)) return;
                $a = array_shift($stack);
                if (empty($stack)) return;
                $b = array_shift($stack);
                array_unshift($stack, $a * $b);
                break;
            // Arithmetic division
            case '/':
                if (empty($stack)) return;
                $a = array_shift($stack);
                if (empty($stack)) return;
                $b = array_shift($stack);
                if ($b == 0) return;
                array_unshift($stack, floor($a / $b));
                break;
            // Arithmetic exponent
            case '^':
                if (empty($stack)) return;
                $a = array_shift($stack);
                if (empty($stack)) return;
                $b = array_shift($stack);
                array_unshift($stack, $a ^ $b);
                break;
            // Greater than
            case '>':
                if (empty($stack)) return;
                $a = array_shift($stack);
                if (empty($stack)) return;
                $b = array_shift($stack);
                array_unshift($stack, $a > $b ? 1 : 0);
                break;
            // Lesser than
            case '<':
                if (empty($stack)) return;
                $a = array_shift($stack);
                if (empty($stack)) return;
                $b = array_shift($stack);
                array_unshift($stack, $a < $b ? 1 : 0);
                break;
            // Comparison
            case '=':
                if (empty($stack)) return;
                $a = array_shift($stack);
                if (empty($stack)) return;
                $b = array_shift($stack);
                array_unshift($stack, $a == $b ? 1 : 0);
                break;
            // Logical OR
            case '|':
                if (empty($stack)) return;
                $a = array_shift($stack);
                if (empty($stack)) return;
                $b = array_shift($stack);
                array_unshift($stack, $a || $b ? 1 : 0);
                break;
            // Logical AND
            case '&':
                if (empty($stack)) return;
                $a = array_shift($stack);
                if (empty($stack)) return;
                $b = array_shift($stack);
                array_unshift($stack, $a && $b ? 1 : 0);
                break;
            // Swap
            case '@':
                if (empty($stack)) return;
                $a = array_shift($stack);
                if (empty($stack)) return;
                $b = array_shift($stack);
                array_unshift($stack, $a);
                array_unshift($stack, $b);
                break;
            // Dup
            case '!':
                if (empty($stack)) return;
                $a = array_shift($stack);
                array_unshift($stack, $a);
                array_unshift($stack, $a);
                break;
            // Drop
            case '#':
                if (empty($stack)) return;
                array_shift($stack);
                break;
            // Hold
            case '(':
                if (empty($stack)) return;
                $a = array_shift($stack);
                array_unshift($hold, $a);
                break;
            // Retrieve
            case ')':
                if (empty($hold)) return;
                $a = array_shift($hold);
                array_unshift($stack, $a);
                break;
            // Exchange
            case '%':
                $tmp = $hold;
                $hold = $stack;
                $stack = $tmp;
                break;
            // Noop
            case '_':
                break;
        }
    }

    return $stack;
}
?>