Ruby script that compiles Brainfuck code into C code.

bf_compiler.rb

def print_help
  puts <<HELP
ruby ./bf_compile.rb [OPTIONS] [NUM_CELLS] file_to_compile.bf
Options:
    -comments     Don't translate Brainfuck comments into C
    -stdlib       Do not use stdlib.h to determine the successful exit status (EXIT_SUCCESSFUL)
    -static       Deactivates the analysis in order to generate a static output for input-independent code.
    -analyzer     Deactivates the analyzer
    +tabs         Used tabs instead of spaces for the indentations
    +cell         See below

NUM_CELLS:    Specify the number of cells. The +cell option must be activated for this. (default 255)
HELP
  exit!
end

if ["help", "-h", "--help"].any? { |s| ARGV.include? s }
  print_help
end

require "erb"

# Template to compile a static program
STATIC_PROG = <<CFILE
#include <stdio.h><% if stdlib %>
#include <stdlib.h><% end %>

int main()
{
<%= ws %>unsigned char arr[] = <%= c_array %>;
<%= ws %>printf("%s", arr);
<%= ws %>return <%= stdlib ?"EXIT_SUCCESS":"0" %>;
}
CFILE

# Arguments, which were partially passed via the command line
flags = [:interpret_comments, :stdlib, :static, :analyzer]
flags.delete :interpret_comments if ARGV.include? "-comments"
flags.delete :stdlib if ARGV.include? "-stdlib"
flags.delete :static if ARGV.include? "-static"
flags.delete :analyzer if ARGV.include? "-analyzer"
flags.push :tabs if ARGV.include? "+tabs"
flags.push :cells if ARGV.include? "+cells"

ws = flags.include?(:tabs) ? "\t" : "    "

puts "Whitespace: #{ws.inspect}"

puts "Reading file..."
filename  = ARGV[-1]
if filename == nil
  puts "No file name was given"
  print_help
elsif ! File.readable?(filename)
  puts "Cannot read file #{filename}"
  exit! false
end

puts "Loading compiler..."
class Compiler
  
  BF_CHARS = "<>+-,.[]".split ""
  IGNORE_CMT_CHARS = "\n\t\r".split ""
  
  C_FILE_BEGIN = <<CFILE
#include <stdio.h><% if @stdlib %>
#include <stdlib.h><% end %>

int main()
{
<%= @whitespace %>unsigned char arr[<%= @num_cells %>];
<%= @whitespace %>for (<%= @stdlib ? "size_t" : "unsigned int" %> i = 0; i < <%= @num_cells %>; i++)
<%= @whitespace %>{
<%= @whitespace * 2 %>arr[i] = 0;
<%= @whitespace %>}
<%= @whitespace %>unsigned char * ptr = arr;
CFILE

  C_FILE_END = <<CFILE
<%= @whitespace %>return <%= @stdlib?"EXIT_SUCCESS":"0" %>;
}
CFILE

  INC_POINTER = <<CFILE
<%= @whitespace * (spaces + 1) %>ptr++;
CFILE

  DEC_POINTER = <<CFILE
<%= @whitespace * (spaces + 1) %>ptr--;
CFILE

  INC_VALUE = <<CFILE
<%= @whitespace * (spaces + 1) %>(*ptr)++;
CFILE

  DEC_VALUE = <<CFILE
<%= @whitespace * (spaces + 1) %>(*ptr)--;
CFILE

  INPUT_CHAR = <<CFILE
<%= @whitespace * (spaces + 1) %>*ptr = getchar();
CFILE

  OUTPUT_CHAR = <<CFILE
<%= @whitespace * (spaces + 1) %>putchar(*ptr);
CFILE

  LOOP_BEGIN = <<CFILE
<%= @whitespace * (spaces + 1) %>while(*ptr)
<%= @whitespace * (spaces + 1) %>{
CFILE

  LOOP_END = <<CFILE
<%= @whitespace * (spaces) %>}
CFILE

  COMMENT_BEGIN = <<CFILE
<%= @whitespace * (nested + 1) %>/* 
CFILE
  COMMENT_BEGIN.chomp!

  COMMENT_END = <<CFILE
 */
CFILE
  
  attr_reader :ccode
  
  def initialize code, num_cells, ws, ic = true, stdlib = true, output = false
    @bf = code
    @num_cells = num_cells
    @ccode = ""
    @whitespace = ws
    @ic = ic
    @stdlib = stdlib
    @output = output
  end
  
  def clear
    @ccode = ""
  end
  
  def compile
    @ccode = ERB.new(C_FILE_BEGIN).result binding

    nested = 0
    cmt = false

    print " " if @output
    @bf.each_char { |c|
      if BF_CHARS.any? { |s| s == c }
        if cmt
          @ccode += ERB.new(COMMENT_END).result binding
          cmt = ! cmt
        end

        print "\b#{c}" if @output
        res = compile_bf_char c, nested
        @ccode += res[0]
        nested += res[1]
      elsif @ic && ! IGNORE_CMT_CHARS.any? { |s| s == c}
        if ! cmt
          @ccode += ERB.new(COMMENT_BEGIN).result binding
          cmt = ! cmt
        end
        @ccode += c
      end
    }
    @ccode += ERB.new(COMMENT_END).result binding if cmt
    @ccode += ERB.new(C_FILE_END).result binding
  end
  
  def compile_bf_char c, spaces
    code = nil
    nested = 0

    case c
    when "<"
      code = ERB.new(DEC_POINTER).result binding
    when ">"
      code = ERB.new(INC_POINTER).result binding
    when "+"
      code = ERB.new(INC_VALUE).result binding
    when "-"
      code = ERB.new(DEC_VALUE).result binding
    when "["
      code = ERB.new(LOOP_BEGIN).result binding
      nested = 1
    when "]"
      code = ERB.new(LOOP_END).result binding
      nested = -1
    when ","
      code = ERB.new(INPUT_CHAR).result binding
    when "."
      code = ERB.new(OUTPUT_CHAR).result binding
    end

    return [code, nested]
  end
end

puts "Loading analyzer..."
class Analyzer
  
  BF_CHARS = "<>+-,.[]".split ""
  
  attr_reader :rounds, :max, :output
  
  def initialize code, process_output = false
    @bf = code
    @code_pointer = 0
    @cells = Array.new
    @pointer = 0
    @rounds = 0
    @max = 1
    @output = []
    @process_output = process_output
  end
  
  def clear
    @code_pointer = 0
    @cells = Array.new
    @pointer = 0
    @rounds = 0
    @max = 1
    @output = []
  end
  
  # The Analyzer works similar to a BF interpreter.
  # However, it does not accept any input. It determines the maximum number of
  # cells, the number of steps and the output.
  def analyze
    loops = []
    while @code_pointer < @bf.length
      c = @bf[@code_pointer]
      print "\b#{c}" if @process_output && BF_CHARS.any? { |s| s == c }
      case c
      when "<"
        @pointer -= 1
      when ">"
        @pointer += 1
      when "+"
        @cells[@pointer] = @cells[@pointer].to_i + 1
      when "-"
        @cells[@pointer] -= 1 if @cells[@pointer].to_i > 0
      when "."
        @output << @cells[@pointer].to_i
      when "["
        loops << @code_pointer
        @code_pointer = find_closing_bracket - 1
      when "]"
        if @cells[@pointer].to_i == 0
          loops.pop
        else
          @code_pointer = loops[-1]
        end
      end
      @code_pointer += 1
      @rounds += 1
      @max = @pointer if @pointer > max
    end
    
    @max += 1
  end
  
  protected
  
  def find_closing_bracket
    counter = 0
    search = @code_pointer + 1
    
    while search < @bf.length
      case @bf[search]
      when "["
        counter += 1
      when "]"
        if counter > 0
          counter -= 1
        else
          break
        end
      end
      search += 1
    end
    
    return search
  end
  
end

bf = File.read filename

num_cells = 255

code = nil
input_indepented_code = ! bf.include?(",")

# If the user allows static compilation, the code does not request any input,
# the use of the analyzer is allowed and no number of cells is specified, then...
if input_indepented_code && flags.include?(:static) && flags.include?(:analyzer) && ! flags.include?(:cells)
  puts "Generating static program... (Use -static option to disable)"
  ana = Analyzer.new bf
  puts "Analying code... (Use -analyzer option to disable)"
  ana.analyze
  if ana.output.empty?
    puts "Program does not contain any output. The compilation is aborted."
    exit! false
  else
    c_array = "\{#{ana.output.join(", ")}, 0\}"
    stdlib = flags.include? :stdlib
    code = ERB.new(STATIC_PROG).result binding
  end
else
  # If the code does not request any input, allows the use of the analyzer and
  # no number of cells is specified, then...
  if input_indepented_code && ! flags.include?(:cells) && flags.include?(:analyzer)
    ana = Analyzer.new bf
    puts "Analying code... (Use -analyzer option to disable)"
    ana.analyze
    num_cells = ana.max
    puts "Number of cells determined by the analyzer: #{ana.max}"
    puts "Number of steps to calculate the output: #{ana.rounds}"
  end
  if flags.include? :cells
    if ARGV[-2]
      num_cells = ARGV[-2].to_i
    else
      puts "The number of cells could not be read. The compilation is canceled."
      exit! false
    end
  end
  
  puts "Number of cells: #{num_cells}"
  puts "Compiling..."
  com = Compiler.new bf, num_cells, ws, flags.include?(:interpret_comments), flags.include?(:stdlib), true
  print "Compile "
  com.compile
  
  print "\n"
  
  code = com.ccode
end

puts "Compiled successfully!"
puts "Writing file..."
File.write "#{filename}.c", code

puts "The full compilation process completed successfully."