BrainFck

pybrainfuck.pybrainfuck()

Runs a BrainF*ck Machine with command line arguments

pybrainfuck.BfCommand(cmd)

Decorates the function with _cmd attribute taken from the arg

class pybrainfuck.BrainFck(**kwargs)

BrainF*ck interpreter/virtual machine

The machine is configurable with following kwargs:

  • cellsize (default: 8) Size in bits of the numeric type to emulate. This types rollover when crossing the 0 and pow(2, cellsize) boundaries

  • totalcells (default: 30000) Size in cells in the virtual machine. Literature shows the default value to be expected by many test scripts

    Set it to 0 for unbounded size

  • extleft (defaults: True): Allow extension to the left. This applies only whilst the array has not reached its full size (if set)

  • prealloc (default: False) If the number of cells is limited, whether to preallocate them

  • wrapover (default: False) Wrap over cells boundaries if totalcells is set and all cells have been allocated (by preallocating or because the totalcells limit has been reached)

  • debug (default: False) Print the status and command to be evaluated

  • linemode (default: False) Read the input in lines and interpret each line as a program skipping blank lines

  • multiline (default: False) In linemode join lines until a blank line is seen

  • comments (default: False) In linemode skip lines starting with commentchar

  • commentchar (default: #) Comment charachter for comments in linemode

  • breakline (default: False) Print a breakline in between the output of the execution of multiple programs

Input/Output:

Controlled also through configuration variables

  • fin (default: sys.stdin) Stream from which input will be read
  • fout (default: sys.stdout) Stream to which input will be printed
  • fdebug (default: fout) Stream to print debug messages to
  • flushout (default: False) Flush out each write (including debug)
Cells/Memory:

  • cells: access to the array of memory cells

    The machine checks boundaries and will not go below 0 or above the maximum total number of cells configured

  • bfnum: class holding the numeric type with the configure bitsize for this machine.

Command Processing:
  • cmd_procs (dict): holds a reference per command to a method to process the command. Automatically filled with methods which have been decorated with BfCommand
Command index:
  • idx (start: -1) Current command index. Increased when a command is read
Constants:
  • maxptr Holds the right limit in cells of the virtual machine
  • csize Length of the numeric value (power of 2 of cellsize)
Status:
  • cmd (start: ‘’) Current command being processed
  • ptr (start: 0) Current cell for get/set/check operations
  • loopskip (start: 0) if > 0, it will skip commands until the matching amount of ‘]’ has been seen. While positive, seeing a ‘[‘ will increase its value by 1
  • loops (start: []) Stores index in input of ‘[‘ commands until they must be skipped
  • loopback (start: -1) If >= 0, the value indicates a jump to such command index

Commands:

Methods decorated with BfCommand(cmd) will be added to a dictionary cmd_procs using cmd as the key.

Method retrieval when a command is read (unless commands are being skipped inside a loop) will be done using the dictionary

The commands manipulate the Status variables

Decoration allows for easy addition of new commands

Internally None is used as a virtual NOP command when the commands inside a loop have to be skipped

Commands are deliberately kept as simple as possible in that they don’t do any memory management or command index manipulation. If such an action may be needed it will tackled by the main loop using the information in the status variables modified by the commands

__init__(**kwargs)

Initializes the machine (not to confuse with resetting the status)

  • It prepares the dictionary of commands
  • It configures the “configuration” variables
  • It sets the constants for maximum pointer length and cell allocation
  • Configures the numeric class
  • Prepares the input/output streams
reset()

Resets the virtual machine to the default status

writeout(*args)
debug_out(*args)
debug_config()

Prints config debug information

debug_status()

Prints status debug information

runfiles(*args)

It opens filenames (args) in read/binary mode to get an unprocessed stream of bytes and executes the program(s)

Parameters:args – paths to files
run(f)

Runs a BrainF*ck program

Parameters:f – file (like) object or string If a string is passed it will be internally converted to a file like object

In non linemode the contents of the file will be executed as a single script

If in linemode the file will be read line by line (skipping empty lines)

If in multiline non-empty lines will be joined until a blank line is seen

If, additionally, in comments mode, then lines starting with the commentschar character will also be skipped

execute(f)

Actual execution of the BrainF*ck program

Parameters:f – file (like) object
The machine is “reset” at the beginning and in each loop

  • Cell (append) memory management is done in dynamic mode (if needed) - To the right if going over the limit - To the left if going below the 0 mark

  • Jumps in program text are performed if needed

  • Next command is fetched

  • On “no command” (EOF) the loop is exited

  • If a command processor exists for the command it is fetched - In case a loop has to be skipped the command processor is fetched

    using the internal NOP command (None)

  • If any command processor has been fetched is invoked

  • If internal numerics are in used, do an overflow check on the cell

mmu_init()
proc_loopskip()

Skips commands until the next closing loop command is found

Loop commands ‘[‘ and ‘]’ seen while looping will be skipped by adding them and substracting them from the loopskip count

proc_increment()

Increments by one the value of the current cell

proc_decrement()

Decrements by one the value of the current cell

proc_whilebegin()

If the current cell is 0, increases the loopskip counter to skip the current loop.

Otherwise it marks the position in the command index seen

proc_whileend()

If the current cell is 0, it removes the entry for the loop start to simply carry on

Otherwise it sets loopback to the command index to jump to

proc_forward()

Increments cell pointer by one

proc_backwards()

Decrements cell pointer by one

proc_output()

Outputs in char format the value of the current cell

proc_input()

Reads input in char format the value of the current cell