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bf2asmjs

A simple brainfuck compiler targeting asm.js.

Compiled examples

http://olahol.github.com/bf2asmjs

BFSelf the self interpreter is the most fun :)

Example

$ python bf2asmjs.py examples/hello.b > bf.js
$ firefox-trunk index.html

Usage

usage: bf2asmjs.py [-h] [--heap HEAP] [--put PUT] [--get GET] file

Compile brainfuck to asm.js.

positional arguments:
  file         brainfuck source file

optional arguments:
  -h, --help   show this help message and exit
  --heap HEAP  number of bytes in the heap, brainfuck usually has at least
               30000
  --put PUT    javascript function implementing .
  --get GET    javascript function implementing ,

Why?

To begin familiarizing myself with targeting asm.js I wanted to create the simplest possible compiler. I'll admit it's not very useful but it got me off the ground and it might help others.

What is asm.js?

Asm.js is a strict subset of javascript meant to be used as a low-level target for compilers. By virtue of being a subset of javascript it can be run on javascript engines that do not support its compilation making it possible to write high performance code that is also backward compatible. Compiled asm.js modules are fast, performing at around 2x of native.

What is brainfuck?

brainfuck is a programming language with a small instruction set and is designed to be as easy as possible to compile.

From Wikipedia

>   increment the data pointer (to point to the next cell to the right).
<   decrement the data pointer (to point to the next cell to the left).
+   increment (increase by one) the byte at the data pointer.
-   decrement (decrease by one) the byte at the data pointer.
.   output the byte at the data pointer.
,   accept one byte of input, storing its value in the byte at the data pointer.
[   if the byte at the data pointer is zero, then instead of moving the
    instruction pointer forward to the next command, jump it forward to the
    command after the matching ] command.
]   if the byte at the data pointer is nonzero, then instead of moving the
    instruction pointer forward to the next command, jump it back to the command
    after the matching [ command.

Heap & Memory.

Asm.js modules use instances of ArrayBuffer as heaps and then create "views" on them to address data. As brainfucks cells are bytes I use the Uint8Array view.

Input & Output

. , is done via the FFI. Default . is writing to an element with id output, default , is reading from an element with id input.