Brainfuck's View of the World — Memory: 30000 cells initialized to 0 — Data pointer: Points to cell — Code: The program that's executed by the machine — Instruction pointer: Points to the next instruction — Input and output streams: STDIN and STDOUT — CPU: Executes the code
The Instruction Set — > - Increment the data pointer by 1 — < - Decrement the data pointer by 1 — + - Increment the value in the current cell — - - Decrement the value in the current cell — . - Print current cell — , - Read a character to current cell — [ - If the current cell contains a zero, jump to matching ] — ] - If the current cell does not contain a zero, jump to matching [
Starting our Interpreter — Interpreters give meaning to symbols by doing what they are supposed to mean — The Brainfuck interpreter manipulates the Brainfuck machine — We need to build the Brainfuck machine
func (m *Machine) Execute() { for m.ip < len(m.code) { ins := m.code[m.ip] switch ins { case '+': m.memory[m.dp]++ case '-': m.memory[m.dp]-- case '>': m.dp++ case '<': m.dp-- } m.ip++ } }
The simplest and slowest solution case '[': if m.memory[m.dp] == 0 { depth := 1 for depth != 0 { m.ip++ switch m.code[m.ip] { case '[': depth++ case ']': depth-- } } }
The Mandelbrot Benchmark $ time ./machine ./mandelbrot.b >/dev/null 68.24s user 0.18s system 99% cpu 1:08.60 total mandelbrot.b A Mandelbrot fractal viewer in Brainfuck Written by Eric Bosman
What if... — ... we had instructions that said "increase by 5" instead of "increase" 5 times? — ... we had an instruction that said "go to this matching bracket if current memory cell is empty"? Spoiler: we'd be faster!
New Instruction Set type InsType byte const ( Plus InsType = '+' Minus InsType = '-' Right InsType = '>' Left InsType = '<' PutChar InsType = '.' ReadChar InsType = ',' JumpIfZero InsType = '[' JumpIfNotZero InsType = ']' ) type Instruction struct { Type InsType Argument int }
Execute - Part 2 func (m *Machine) Execute() { // ... case PutChar: for i := 0; i < ins.Argument; i++ { m.putChar() } case ReadChar: for i := 0; i < ins.Argument; i++ { m.readChar() } // ... }
Compiler Wikipedia says: a computer program (or a set of programs) that transforms source code written in a programming language (the source language) into another computer language (the target language)
Problems when compiling loops — NOT foldable. We can't turn [[[]]] into [] — NOT countable. Instructions in beetween might change. — NOT stateless. We have to remember positions.
Solution — "[" — emit a JumpIfZero instruction — Argument will be 0 -- a placeholder value — "]" — emit JumpIfNotZero with correct argument — change JumpIfZero argument to correct position
Solution — "[" — emit a JumpIfZero instruction — Argument will be 0 -- a placeholder value — "]" — emit JumpIfNotZero with correct argument — change JumpIfZero argument to correct position How do we keep track of JumpIfZero instructions? Solution to problem in solution: with a stack! Stack, the data structure. First in, last out.
func (c *Compiler) Compile() []*Instruction { // [...] case ']': // Pop position of last JumpIfZero ("[") instruction off stack openInstruction := loopStack[len(loopStack)-1] loopStack = loopStack[:len(loopStack)-1] // Emit the new JumpIfNotZero ("]") instruction, // with correct position as argument closeInstructionPos := c.EmitWithArg(JumpIfNotZero, openInstruction) // Patch the old JumpIfZero ("[") instruction with new position c.instructions[openInstruction].Argument = closeInstructionPos // [...] }
Make Eric proud! — brainfuck optimzation strategies: http://calmerthanyouare.org/ 2015/01/07/optimizing-brainfuck.html — Hello, JIT World: The Joy Of Simple JITs: http:// blog.reverberate.org/2012/12/hello-jit-world-joy-of-simple-jits.html — interpreter, compiler, jit: https://nickdesaulniers.github.io/blog/ 2015/05/25/interpreter-compiler-jit/ — a optimized brainfuck compiler written in sed: https://github.com/ stedolan/bf.sed — the original Brainfuck distribution: https://gist.github.com/ rdebath/0ca09ec0fdcf3f82478f — there's much, much more
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