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
    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.
   $s, $_s  Source string and pointer (current position)
   $d, $_d  Data   array  and pointer
   $i, $_i  Input  string and pointer
   $o       Output string

function brainfuck_debug(&$s, &$_s, &$d, &$_d, &$i, &$_i, &$o) {
$d as $element => $value) {
"<td align=\"center\">" . $element . "</td>\n";
"<td align=\"center\">" . ord($value) . "</td>\n";
"<td align=\"center\">" . (ord($value) >= 32 ? htmlentities($value) : "&nbsp;") . "</td>\n";

/* The actual interpreter */

function brainfuck_interpret(&$s, &$_s, &$d, &$_d, &$i, &$_i, &$o) {
   do {
$s[$_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;
'-': $d[$_d] = chr(ord($d[$_d]) - 1); break;
'>': $_d++; if(!isset($d[$_d])) $d[$_d] = chr(0); break;
'<': $_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;
$brackets && $_s++ < strlen($s)) {
$s[$_s] == '[')
             else if(
$s[$_s] == ']')
/* 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 = $pos;
/* Return true when loop has to be executed again. It is redundant to the [ checking, but
          it will save some parsing time (otherwise the interpreter would have to return to [ only
          to skip all characters again) */
case ']': return ((int)ord($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 */

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,