Create a gist now

Instantly share code, notes, and snippets.

What would you like to do?
Simplified Brainfuck interpreter in C++11
/*
Copyright (c) 2015 Kristopher Johnson
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#include <fstream>
#include <iostream>
#include <iterator>
#include <stdexcept>
#include <string>
#include <vector>
using std::cerr;
using std::cin;
using std::cout;
using std::endl;
using std::exception;
using std::ifstream;
using std::istreambuf_iterator;
using std::ios;
using std::runtime_error;
using std::string;
using std::vector;
class BrainfuckMachine
{
public:
explicit BrainfuckMachine(const string& sourceFilePath)
{
loadProgramFromFilePath(sourceFilePath);
}
void executeProgram()
{
tapePosition = 0;
tape.clear();
ProgramCounter pc = 0;
while (pc < program.size()) {
auto instruction = program[pc];
++pc;
switch (instruction) {
case '>': ++tapePosition;
break;
case '<': --tapePosition;
break;
case '+': ++markAtTapePosition();
break;
case '-': --markAtTapePosition();
break;
case '.': cout.put(markAtTapePosition());
break;
case ',': readInputCharacter();
break;
case '[': if (markAtTapePosition() == 0) pc = matchingCloseBrace(pc);
break;
case ']': if (markAtTapePosition() != 0) pc = matchingOpenBrace(pc);
break;
default: // ignore other characters
break;
}
}
}
private:
// The "tape" is a vector of 8-bit marks.
// The vector is automatically resized as the tape position increases.
// We use a signed type for the index so that we can catch underflow.
using TapeMark = char;
using Tape = vector<TapeMark>;
using TapePosition = int;
// The "program" is a vector of 8-bit instructions.
// The instructions are '<', '>', '+', '-', '.', ',', '[', and ']'
using Instruction = char;
using Program = vector<Instruction>;
using ProgramCounter = Program::size_type;
Tape tape;
TapePosition tapePosition = 0;
Program program;
TapeMark& markAtTapePosition()
{
if (tapePosition < 0)
throw runtime_error("tape position < 0");
auto pos = static_cast<Tape::size_type>(tapePosition);
// Tape extends as needed
if (tape.size() <= pos)
tape.resize(pos + 128);
return tape[pos];
}
void loadProgramFromFilePath(const string& sourceFilePath)
{
auto sourceFile = ifstream(sourceFilePath, ios::in | ios::binary);
if (sourceFile.fail())
throw runtime_error(string("unable to open file at path \"")
+ sourceFilePath
+ "\"");
program.assign(istreambuf_iterator<char>(sourceFile),
istreambuf_iterator<char>());
}
void readInputCharacter()
{
auto input = cin.get();
if (input != EOF)
markAtTapePosition() = static_cast<TapeMark>(input);
}
ProgramCounter matchingCloseBrace(ProgramCounter pc)
{
auto nest = 1;
while (pc < program.size() && nest > 0) {
auto instruction = program[pc];
if (instruction == ']')
--nest;
else if (instruction == '[')
++nest;
++pc;
}
if (nest > 0)
throw runtime_error("unmatched [");
return pc;
}
ProgramCounter matchingOpenBrace(ProgramCounter pc)
{
auto nest = 1;
--pc;
while (pc > 0 && nest > 0) {
--pc;
auto instruction = program[pc];
if (instruction == '[')
--nest;
else if (instruction == ']')
++nest;
}
if (nest > 0)
throw runtime_error("unmatched ]");
++pc;
return pc;
}
};
int main(int argc, const char * argv[])
{
if (argc < 2) {
cerr << "usage: " << argv[0] << " FILENAME ..." << endl;
}
else for (auto i = 1; i < argc; ++i) {
auto sourceFilePath = argv[i];
try {
auto machine = BrainfuckMachine(sourceFilePath);
machine.executeProgram();
}
catch (const exception& ex) {
cerr << sourceFilePath << ": error: " << ex.what() << endl;
}
}
return 0;
}
CXXFLAGS=--std=c++11 -O2 -Wall
all: KJSimpleBrainfuck
KJSimpleBrainfuck: KJSimpleBrainfuck.cpp
# Should print "OK"
test: all
./KJSimpleBrainfuck OK.bf
clean:
- /bin/rm KJSimpleBrainfuck
.PHONY: all test clean
This simple Brainfuck program writes "OK" and a newline
++++[>++++<-]>[<+++++>-]< Put 80 onto tape at position 0
-.----. Write 79 ('O') then 75 ('K')
>+++++ +++++. Write newline
@kristopherjohnson

This is a simplified version of the KJBrainfuck.cpp interpreter available here: https://gist.github.com/kristopherjohnson/e5fc3d19c251dc561f62

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment