brainfuck.php

<?php

/*

    Brainfuck interpreter in PHP
    Copyright (C) 2002 Daniel Lorch

    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 2 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, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

*/


/**
 * Debug function displays valuable debug information.
 * Rewrite this if desired.
 *
 * @param string $s Source string
 * @param int $_s Source string pointer (current position)
 * @param array $d Data array
 * @param int $_d Data array pointer
 * @param string $i Input string
 * @param int $_i Input  pointer
 * @param string $o Output string
 */
function brainfuck_debug(&$s, &$_s, &$d, &$_d, &$i, &$_i, &$o)
{
    echo "<table>\n";
    echo "<tr><th>Position</th><th>Value</th><th>ASCII</th></tr>\n";

    foreach ($d as $element => $value) {
        echo "<tr>\n";
        echo '<td style="text-align: center">' . $element . "</td>\n";
        echo '<td style="text-align: center">' . ord($value) . "</td>\n";
        echo '<td style="text-align: center">' . (ord($value) >= 32 ? htmlentities($value) : "&nbsp;") . "</td>\n";
        echo "</tr>\n";
    }

    echo "</table>\n";
}

/**
 * The actual interpreter
 *
 * @param string $s Source string
 * @param int $_s Source string pointer (current position)
 * @param array $d Data array
 * @param int $_d Data array pointer
 * @param string $i Input string
 * @param int $_i Input  pointer
 * @param string $o Output string
 */
function brainfuck_interpret(&$s, &$_s, &$d, &$_d, &$i, &$_i, &$o)
{
    do {
        switch ($s[$_s]) {
            /* Execute brainfuck commands. Values are not stored as numbers, but as their
               representing characters in the ASCII table. This is perfect, as chr(256) is
               automagically converted to chr(0). */
            case '+':
                $d[$_d] = chr(ord($d[$_d]) + 1);
                break;
            case '-':
                $d[$_d] = chr(ord($d[$_d]) - 1);
                break;
            case '>':
                $_d++;
                if (!isset($d[$_d])) $d[$_d] = chr(0);
                break;
            case '<':
                $_d--;
                break;

            /* Output is stored in a variable. Change this to
                 echo $d[$_d]; flush();
               if you would like to have a "live" output (when running long calculations, for example.
               Or if you are just terribly impatient). */
            case '.':
                $o .= $d[$_d];
                break;

            /* Due to PHP's non-interactive nature I have the whole input passed over in a string.
               I successively read characters from this string and pass it over to BF every time a
               ',' command is executed. */
            case ',':
                $d[$_d] = $_i == strlen($i) ? chr(0) : $i[$_i++];
                break;

            /* Catch loops */
            case '[':
                /* Skip loop (also nested ones) */
                if ((int)ord($d[$_d]) == 0) {
                    $brackets = 1;
                    while ($brackets && $_s++ < strlen($s)) {
                        if ($s[$_s] == '[')
                            $brackets++;
                        else if ($s[$_s] == ']')
                            $brackets--;
                    }
                } /* Execute loop */
                else {
                    $pos = $_s++ - 1;
                    /* The closing ] returns true when the loop has to be executed again. If so, then return
                       to the $pos(ition) where the opening [ is. */
                    if (brainfuck_interpret($s, $_s, $d, $_d, $i, $_i, $o))
                        $_s = $pos;
                }
                break;
            /* Return true when loop has to be executed again. It is redundant to the [ checking, but
               it will save some parsing time (otherwise the interpreter would have to return to [ only
               to skip all characters again) */
            case ']':
                return ((int)ord($d[$_d]) != 0);
            /* Call debug function */
            case '#':
                brainfuck_debug($s, $_s, $d, $_d, $i, $_i, $o);
        }
    } while (++$_s < strlen($s));
}

/**
 * Call this one in order to interpret brainfuck code
 *
 * @param string $source source data
 * @param string $input Simulate stdin
 * @return string the output
 */
function brainfuck($source, $input = '')
{

    /* Define needed variables:

       $data    Brainfuck's memory
       $source  Source data
       $input   Simulate STDIN
       $output  Save output in here

       Each with according index variables
    */

    $data = array();
    $data[0] = chr(0); /* It is necessary to set every element explicitly, as
                             PHP treats arrays as hashes */
    $data_index = 0;

    $source_index = 0;

    $input_index = 0;

    $output = '';

    /* Call the actual interpreter */
    brainfuck_interpret(
        $source,
        $source_index,
        $data,
        $data_index,
        $input,
        $input_index,
        $output
    );

    return $output;
}