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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) {
echo "<table>\n";
echo "<tr><td><b>Position</b></td><td><b>Value</b></td><td><b>ASCII</b></td></tr>\n";
foreach($d as $element => $value) {
echo "<tr>\n";
echo "<td align=\"center\">" . $element . "</td>\n";
echo "<td align=\"center\">" . ord($value) . "</td>\n";
echo "<td align=\"center\">" . (ord($value) >= 32 ? htmlentities($value) : "&nbsp;") . "</td>\n";
echo "</tr>\n";
echo "</table>\n";
/* The actual interpreter */
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] == '[')
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,
return $output;
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