bfi 1.0.4

Description:

bfi 1.0.4

This is a pure python interpreter for the
Brainfuck esoteric programming
language. bfi is quite fast without requiring any special python implementations
or compiled extension modules. bfi Supports Python 2x and 3x.
bfi achieves a significant speedup in the execution of brainfuck
programs by first compiling brainfuck source code into an intermediate form.
This intermediate form takes advantage of common brainfuck programming constructs
to execute much faster than if we were to interpret & execute the brainfuck source directly.
Take moving the cell pointer, as a relativey simple example; to execute <<<<<<<<<<,
we could iterate over each < character, and perform 10 separate “cell pointer decrement”
operations. This would be the slow option. Alternatively, we could collapse those 10 instructions
into a single instruction to decrement the cell pointer by 10 in a single operation. This is
generally how the opcodes for the intermediate form work. All runs of cell pointer
increment/decrements are collapsed like this, as well as several other similar optimizations.

Speed benchmark
Here is a quick comparison between bfi and two other popular pure-python
brainfuck interpreters on github. The time shown is the time that each
interpreter took to complete the “Towers of Hanoi” program (hanoi.b,
available in the examples directory):


Interpreter name
Time to complete hanoi.b



bfi
1 minute, 9 seconds

pocmo’s interpreter
28 minutes, 51 seconds

alexprengere’s intrepreter
1 hour, 7 minutes, 54 seconds



(I should note here that alexprengere’s interpreter can actually go
much faster than this, but not without using the alternative PyPy interpreter,
or compiling some stuff. Speeds here are shown without such modifications.
All tests were done using the standard CPython 2.7.14 interpreter)


Implementation details

No change on EOF
Tape size is configurable, default is 30,000 cells
Cells are one byte, valid values between 0-255. Overflow/underflow wraps
around



Installing
Use pip to install:
pip install bfi


Using the interpreter from the command-line
Once installed, the brainfuck interpreter can be invoked from the command line
using the bfi command. Just run bfi and pass a brainfuck source file.
Several sample Brainfuck programs are provided in the examples directory
within the installed package (in your system’s python2.7/dist-packages
directory- on linux-based systems, for example, the full path might be
/usr/local/lib/python2.7/dist-packages/bfi/examples).
In the sample commands below, we will run “Lost Kingdom”, a text-based adventure
game written in Brainfuck:
$> cd <dist-packages-directory>/bfi/examples
$> bfi LostKingdom.b


Using the interpreter in your own code
Here is how you use the bfi module to execute some Brainfuck code
normally (reading data directly from stdin and writing directly to stdout):
>>> import bfi
>>> with open('samples/hello_world.b', 'r') as fh:
... brainfuck_code = fh.read()
...
>>> Brainfuck.interpret(brainfuck_code)

Hello World!
Here is how you use the bfi module to execute some Brainfuck code without
reading/writing the user’s terminal; input is passed a parameter to
interpret(), and any output is returned as a string.
>>> input_data = "test input"
>>> ret = bfi.interpret(brainfuck_code, stdin=input_data, buffer_stdout=True)
>>> print ret

Hello World!


Reference
Documentation for the python API is here: https://bfi.readthedocs.io


Gratuitous unnecessary extras
In order to make Brainfuck code execute more efficiently, it is compiled into
an intermediate form that takes advantage of common brainfuck idioms and
constructs. This intermediate form consists of 11 opcodes, 8 of which are
similar to the original 8 brainfuck instructions. The following table describes
the opcodes:


Opcode
Description



move <off> <num>
Moves the cell pointer by <num>
cells. <off> is unused

sub <off> <num>
Moves the cell pointer by <off>, and
decrements value of current cell by
<num> cells

add <off> <num>
Moves the cell pointer by <off>, and
increments value of current cell by
<num> cells

open <off> <location>
<location> is an index into the list
of program opcodes. If the value of
current cell is zero, jump to
<location>. Otherwise, continue
execution normally (Same functionality
as brainfuck “[” instruction, except
jump location is stored with opcode).
<off> is unused

close <off> <location>
<location> is an index into the list
of program opcodes. If the value of
current cell is zero, continue execution
normally. Otherwise, jump to
<location> (Same functionality as
brainfuck “]” instruction, except jump
location is stored with opcode). In all
cases the cell pointer will be moved by
<off>

input <off>
Moves the cell pointer by <off>,
then reads one character of input and
writes to current cell

output <off>
Moves the cell pointer by <off>,
then prints value of current cell as
an ASCII character

clear <off>
Moves the cell pointer by <off>,
then sets the value of current cell to
zero

copy <off> {<o>:<m>,... }
Moves the cell pointer by <off>,
then for each key/value pair, sets the
value of the cell at (current cell +
<o>) to be (value of current cell *
<m>)

scanl <off>
Moves the cell pointer by <off>,
then decrements the cell pointer until
it points at a cell containing 0

scanr <off>
Moves the cell pointer by <off>,
then increments the cell pointer until
it points at a cell containing 0



If you really want to, you can actually view a brainfuck program in this
intermediate form, by using the bfi.parse method and printing the resulting
opcodes:
>>> with open('bfi/examples/mandel.b', 'r') as fh:
... program = fh.read()
...
>>> opcodes = bfi.parse(program)
>>> for c in opcodes: print c
...

add 0 13
copy 0 {1: 2, 4: 5, 5: 2, 6: 1}
add 5 6
sub 1 3
add 10 15
open 0 12
open 0 7
close 9 6
add 0 1
open 0 10

... (long output, truncated ...)
And of course, you can execute the compiled opcodes as many times as you like
using bfi.execute.


Example Brainfuck programs
I have included several random Brainfuck programs that I’ve found in various
places. I didn’t write any of these programs, I just copied them as-is
from other public sources. Descriptive comments (and author’s name, in some
cases) can be seen in the Brainfuck source files themselves.
A description of the example Brainfuck programs included with this package
follows:

bfcl.bf: A Brainfuck-to-ELF translator, in Brainfuck. Reads in Brainfuck
source from stdin and writes a Linux ELF file to stdout
bitwidth.bf Assorted tests for Brainfuck interpreter/compiler correctness
collatz.b A demonstration of the Collatz problem in Brainfuck
eoftest.b Tests EOF behaviour of brainfuck interpreters/compilers
fib.b Prints a neverending fibonacci sequence
gameoflife.b Conway’s Game of Life in Brainfuck
hanoi.b Towers of Hanoi in Brainfuck
hello_world.b Classic “hello, world!” in Brainfuck
LostKingdom.b A text-based adventure game in Brainfuck
mandel.b An ASCII mandelbrot fractal set viewer in Brainfuck
numwarp.b Prints an enlarged ASCII representation of numbers entered by
the user
primes.bf Prints prime numbers
rot13.b Prints the ROT13 encoding of the string entered by the user
sierpinksi.b Displays the Sierpinksi triangle
TheBrainfuckedLoneWolf.b ASCII asteroids-inspired top-down shooter game
in Brainfuck