h/plugins/bf.py

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'''brainfuck interpreter adapted from (public domain) code at
http://brainfuck.sourceforge.net/brain.py'''
import re
import random
from util import hook
BUFFER_SIZE = 5000
MAX_STEPS = 1000000
@hook.command
def bf(inp):
".bf <prog> -- executes brainfuck program <prog>"""
program = re.sub('[^][<>+-.,]', '', inp)
# create a dict of brackets pairs, for speed later on
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brackets = {}
open_brackets = []
for pos in range(len(program)):
if program[pos] == '[':
open_brackets.append(pos)
elif program[pos] == ']':
if len(open_brackets) > 0:
brackets[pos] = open_brackets[-1]
brackets[open_brackets[-1]] = pos
open_brackets.pop()
else:
return 'unbalanced brackets'
if len(open_brackets) != 0:
return 'unbalanced brackets'
# now we can start interpreting
ip = 0 # instruction pointer
mp = 0 # memory pointer
steps = 0
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memory = [0] * BUFFER_SIZE # initial memory area
rightmost = 0
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output = "" # we'll save the output here
# the main program loop:
while ip < len(program):
c = program[ip]
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if c == '+':
memory[mp] = memory[mp] + 1 % 256
elif c == '-':
memory[mp] = memory[mp] - 1 % 256
elif c == '>':
mp += 1
if mp > rightmost:
rightmost = mp
if mp >= len(memory):
# no restriction on memory growth!
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memory.extend([0] * BUFFER_SIZE)
elif c == '<':
mp = mp - 1 % len(memory)
elif c == '.':
output += chr(memory[mp])
if len(output) > 500:
break
elif c == ',':
memory[mp] = random.randint(1, 255)
elif c == '[':
if memory[mp] == 0:
ip = brackets[ip]
elif c == ']':
if memory[mp] != 0:
ip = brackets[ip]
ip += 1
steps += 1
if steps > MAX_STEPS:
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if output == '':
output = '(no output)'
output += '[exceeded %d iterations]' % MAX_STEPS
break
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stripped_output = re.sub(r'[\x00-\x1F]', '', output)
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if stripped_output == '':
if output != '':
return 'no printable output'
return 'no output'
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return stripped_output[:430].decode('utf8', 'ignore')