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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `examples/bf.rs`."><title>bf.rs - source</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../static.files/rustdoc-b0742ba02757f159.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="bf" data-themes="" data-resource-suffix="" data-rustdoc-version="1.83.0 (90b35a623 2024-11-26)" data-channel="1.83.0" data-search-js="search-f0d225181b97f9a4.js" data-settings-js="settings-805db61a62df4bd2.js" ><script src="../../static.files/storage-1d39b6787ed640ff.js"></script><script defer src="../../static.files/src-script-e66d777a5a92e9b2.js"></script><script defer src="../../src-files.js"></script><script defer src="../../static.files/main-f070b9041d14864c.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-0111fcff984fae8f.css"></noscript><link rel="alternate icon" type="image/png" href="../../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc src"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="src-sidebar-title"><h2>Files</h2></div></nav><div class="sidebar-resizer"></div><main><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><h1><div class="sub-heading">bf/</div>bf.rs</h1><rustdoc-toolbar></rustdoc-toolbar></div><div class="example-wrap"><div data-nosnippet><pre class="src-line-numbers">
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<a href="#411" id="411">411</a></pre></div><pre class="rust"><code><span class="doccomment">//! Brainfuck VM.
//!
//! This example implements a simple [brainfuck][bf] interpreter
//! [`BrainfuckInterp`] and a jit compiler [`BrainfuckJit`].
//!
//! Brainfuck is an esoteric programming languge existing of 8 commands.
//! - `>` increment data pointer.
//! - `<` decrement data pointer.
//! - `+` increment data at current data pointer.
//! - `-` decrement data at current data pointer.
//! - `.` output data at current data pointer.
//! - `,` read input and store at current data pointer.
//! - `[` jump behind matching `]` if data at data pointer is zero.
//! - `]` jump behind matching `[` if data at data pointer is non-zero.
//!
//! The following is the `hello-world` program from [wikipedia][hw].
//! ```
//! ++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.
//! ```
//!
//! [bf]: https://en.wikipedia.org/wiki/Brainfuck
//! [hw]: https://en.wikipedia.org/wiki/Brainfuck#Hello_World!
</span><span class="kw">use </span>std::collections::HashMap;
<span class="kw">use </span>std::io::Write;
<span class="kw">use </span>juicebox_asm::insn::<span class="kw-2">*</span>;
<span class="kw">use </span>juicebox_asm::Runtime;
<span class="kw">use </span>juicebox_asm::{Asm, Imm64, Imm8, Label, Mem8, Reg64, Reg8};
<span class="comment">// -- BRAINFUCK INTERPRETER ----------------------------------------------------
</span><span class="kw">struct </span>BrainfuckInterp {
pc: usize,
imem: Vec<char>,
dptr: usize,
dmem: [u8; <span class="number">256</span>],
branches: HashMap<usize, usize>,
}
<span class="kw">impl </span>BrainfuckInterp {
<span class="kw">fn </span>new(prog: <span class="kw-2">&</span>str) -> <span class="prelude-ty">Result</span><<span class="self">Self</span>, String> {
<span class="comment">// Do a first pass over the bf program to filter whitespace and detect
// invalid tokens. Additionally validate all conditional branches, and
// compute their branch targets.
</span><span class="kw">let </span>(imem, branches) = {
<span class="comment">// Instruction memory holding the final bf program.
</span><span class="kw">let </span><span class="kw-2">mut </span>imem = Vec::new();
<span class="comment">// Helper to track index of open brackets.
</span><span class="kw">let </span><span class="kw-2">mut </span>lhs_brackets = Vec::new();
<span class="comment">// Mapping from branch instruction to branch target.
</span><span class="kw">let </span><span class="kw-2">mut </span>branches = HashMap::new();
<span class="kw">for </span>(idx, token) <span class="kw">in </span>prog.chars().filter(|c| !c.is_whitespace()).enumerate() {
<span class="kw">match </span>token {
<span class="string">'<' </span>| <span class="string">'>' </span>| <span class="string">'+' </span>| <span class="string">'-' </span>| <span class="string">'.' </span>| <span class="string">',' </span>=> { <span class="comment">/* ignore valid bf tokens */ </span>}
<span class="string">'[' </span>=> lhs_brackets.push(idx),
<span class="string">']' </span>=> {
<span class="kw">if let </span><span class="prelude-val">Some</span>(lhs) = lhs_brackets.pop() {
branches.insert(lhs, idx);
branches.insert(idx, lhs);
} <span class="kw">else </span>{
<span class="kw">return </span><span class="prelude-val">Err</span>(<span class="macro">format!</span>(<span class="string">"encountered un-balanced brackets, found ']' at index {idx} without matching '['"</span>));
}
}
<span class="kw">_ </span>=> <span class="kw">return </span><span class="prelude-val">Err</span>(<span class="macro">format!</span>(<span class="string">"invalid bf token '{token}'"</span>)),
}
imem.push(token)
}
<span class="kw">if </span>!lhs_brackets.is_empty() {
<span class="kw">return </span><span class="prelude-val">Err</span>(String::from(
<span class="string">"encountered un-balanced brackets, left-over '[' after parsing bf program"</span>,
));
}
(imem, branches)
};
<span class="prelude-val">Ok</span>(BrainfuckInterp {
pc: <span class="number">0</span>,
imem,
dptr: <span class="number">0</span>,
dmem: [<span class="number">0</span>; <span class="number">256</span>],
branches,
})
}
}
<span class="kw">fn </span>run_interp(prog: <span class="kw-2">&</span>str) {
<span class="kw">let </span><span class="kw-2">mut </span>vm = BrainfuckInterp::new(prog).unwrap();
<span class="kw">loop </span>{
<span class="kw">let </span>insn = <span class="kw">match </span>vm.imem.get(vm.pc) {
<span class="prelude-val">Some</span>(insn) => insn,
<span class="prelude-val">None </span>=> <span class="kw">break</span>, <span class="comment">// End of bf program.
</span>};
<span class="kw">let </span>putchar = |val: u8| {
std::io::stdout()
.write(<span class="kw-2">&</span>[val])
.expect(<span class="string">"Failed to write to stdout!"</span>);
};
<span class="kw">match </span>insn {
<span class="string">'>' </span>=> {
vm.dptr += <span class="number">1</span>;
<span class="macro">assert!</span>(vm.dptr < vm.dmem.len());
}
<span class="string">'<' </span>=> {
<span class="macro">assert!</span>(vm.dptr > <span class="number">0</span>);
vm.dptr -= <span class="number">1</span>;
}
<span class="string">'+' </span>=> {
vm.dmem[vm.dptr] += <span class="number">1</span>;
}
<span class="string">'-' </span>=> {
vm.dmem[vm.dptr] -= <span class="number">1</span>;
}
<span class="string">'.' </span>=> {
putchar(vm.dmem[vm.dptr]);
}
<span class="string">',' </span>=> {
<span class="macro">unimplemented!</span>(<span class="string">"getchar"</span>);
}
<span class="string">'[' </span>=> {
<span class="kw">if </span>vm.dmem[vm.dptr] == <span class="number">0 </span>{
vm.pc = <span class="kw-2">*</span>vm.branches.get(<span class="kw-2">&</span>vm.pc).unwrap();
}
}
<span class="string">']' </span>=> {
<span class="kw">if </span>vm.dmem[vm.dptr] != <span class="number">0 </span>{
vm.pc = <span class="kw-2">*</span>vm.branches.get(<span class="kw-2">&</span>vm.pc).unwrap();
}
}
<span class="kw">_ </span>=> <span class="macro">unreachable!</span>(),
}
vm.pc += <span class="number">1</span>;
}
}
<span class="comment">// -- BRAINFUCK JIT ------------------------------------------------------------
</span><span class="attr">#[cfg(not(any(target_arch = <span class="string">"x86_64"</span>, target_os = <span class="string">"linux"</span>)))]
</span><span class="macro">compile_error!</span>(<span class="string">"Only supported on x86_64 with SystemV abi"</span>);
<span class="kw">struct </span>BrainfuckJit {
imem: Vec<char>,
dmem: [u8; <span class="number">256</span>],
}
<span class="kw">impl </span>BrainfuckJit {
<span class="kw">fn </span>new(prog: <span class="kw-2">&</span>str) -> <span class="prelude-ty">Result</span><<span class="self">Self</span>, String> {
<span class="comment">// Do a first pass over the bf program to filter whitespace and detect
// invalid tokens.
</span><span class="kw">let </span>imem = prog
.chars()
.filter(|c| !c.is_whitespace())
.map(|c| <span class="kw">match </span>c {
<span class="string">'<' </span>| <span class="string">'>' </span>| <span class="string">'+' </span>| <span class="string">'-' </span>| <span class="string">'.' </span>| <span class="string">',' </span>| <span class="string">'[' </span>| <span class="string">']' </span>=> <span class="prelude-val">Ok</span>(c),
<span class="kw">_ </span>=> <span class="prelude-val">Err</span>(<span class="macro">format!</span>(<span class="string">"invalid bf token '{c}'"</span>)),
})
.collect::<<span class="prelude-ty">Result</span><Vec<char>, String>>()<span class="question-mark">?</span>;
<span class="prelude-val">Ok</span>(BrainfuckJit {
imem,
dmem: [<span class="number">0</span>; <span class="number">256</span>],
})
}
}
<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn </span>putchar(c: u8) {
std::io::stdout()
.write(<span class="kw-2">&</span>[c])
.expect(<span class="string">"Failed to write to stdout!"</span>);
}
<span class="kw">fn </span>run_jit(prog: <span class="kw-2">&</span>str) {
<span class="kw">let </span><span class="kw-2">mut </span>vm = BrainfuckJit::new(prog).unwrap();
<span class="comment">// Use callee saved registers to hold vm state, such that we don't need to
// save any state before calling out to putchar.
</span><span class="kw">let </span>dmem_base = Reg64::rbx;
<span class="kw">let </span>dmem_size = Reg64::r12;
<span class="kw">let </span>dmem_idx = Reg64::r13;
<span class="kw">let </span><span class="kw-2">mut </span>asm = Asm::new();
<span class="comment">// Save callee saved registers before we tamper them.
</span>asm.push(dmem_base);
asm.push(dmem_size);
asm.push(dmem_idx);
<span class="comment">// Move data memory pointer (argument on jit entry) into correct register.
</span>asm.mov(dmem_base, Reg64::rdi);
<span class="comment">// Move data memory size (compile time constant) into correct register.
</span>asm.mov(dmem_size, Imm64::from(vm.dmem.len()));
<span class="comment">// Clear data memory index.
</span>asm.xor(dmem_idx, dmem_idx);
<span class="comment">// A stack of label pairs, used to link up forward and backward jumps for a
// given '[]' pair.
</span><span class="kw">let </span><span class="kw-2">mut </span>label_stack = Vec::new();
<span class="comment">// Label to jump to when a data pointer overflow is detected.
</span><span class="kw">let </span><span class="kw-2">mut </span>oob_ov = Label::new();
<span class="comment">// Label to jump to when a data pointer underflow is detected.
</span><span class="kw">let </span><span class="kw-2">mut </span>oob_uv = Label::new();
<span class="comment">// Generate code for each instruction in the bf program.
</span><span class="kw">let </span><span class="kw-2">mut </span>pc = <span class="number">0</span>;
<span class="kw">while </span>pc < vm.imem.len() {
<span class="kw">match </span>vm.imem[pc] {
<span class="string">'>' </span>=> {
asm.inc(dmem_idx);
<span class="comment">// Check for data pointer overflow and jump to error handler if needed.
</span>asm.cmp(dmem_idx, dmem_size);
asm.jz(<span class="kw-2">&mut </span>oob_ov);
}
<span class="string">'<' </span>=> {
<span class="comment">// Check for data pointer underflow and jump to error handler if needed.
</span>asm.test(dmem_idx, dmem_idx);
asm.jz(<span class="kw-2">&mut </span>oob_uv);
asm.dec(dmem_idx);
}
<span class="string">'+' </span>=> {
<span class="comment">// Apply optimization to fold consecutive '+' instructions to a
// single add instruction during compile time.
</span><span class="kw">match </span>vm.imem[pc..].iter().take_while(|&&i| i.eq(<span class="kw-2">&</span><span class="string">'+'</span>)).count() {
<span class="number">1 </span>=> {
asm.inc(Mem8::indirect_base_index(dmem_base, dmem_idx));
}
cnt <span class="kw">if </span>cnt <= u8::MAX <span class="kw">as </span>usize => {
asm.add(
Mem8::indirect_base_index(dmem_base, dmem_idx),
Imm8::from(cnt <span class="kw">as </span>u8),
);
<span class="comment">// Advance pc, but account for pc increment at the end
// of the loop.
</span>pc += cnt - <span class="number">1</span>;
}
cnt @ <span class="kw">_ </span>=> <span class="macro">unimplemented!</span>(<span class="string">"cnt={cnt} oob, add with larger imm"</span>),
}
}
<span class="string">'-' </span>=> {
<span class="comment">// Apply optimization to fold consecutive '-' instructions to a
// single sub instruction during compile time.
</span><span class="kw">match </span>vm.imem[pc..].iter().take_while(|&&i| i.eq(<span class="kw-2">&</span><span class="string">'-'</span>)).count() {
<span class="number">1 </span>=> {
asm.dec(Mem8::indirect_base_index(dmem_base, dmem_idx));
}
cnt <span class="kw">if </span>cnt <= u8::MAX <span class="kw">as </span>usize => {
asm.sub(
Mem8::indirect_base_index(dmem_base, dmem_idx),
Imm8::from(cnt <span class="kw">as </span>u8),
);
<span class="comment">// Advance pc, but account for pc increment at the end
// of the loop.
</span>pc += cnt - <span class="number">1</span>;
}
cnt @ <span class="kw">_ </span>=> <span class="macro">unimplemented!</span>(<span class="string">"cnt={cnt} oob, sub with larger imm"</span>),
}
}
<span class="string">'.' </span>=> {
<span class="comment">// Load data memory from active cell into di register, which is
// the first argument register according to the SystemV abi,
// then call into putchar. Since we stored all out vm state in
// callee saved registers we don't need to save any registers
// before the call.
</span>asm.mov(Reg8::dil, Mem8::indirect_base_index(dmem_base, dmem_idx));
asm.mov(Reg64::rax, Imm64::from(putchar <span class="kw">as </span>usize));
asm.call(Reg64::rax);
}
<span class="string">',' </span>=> {
<span class="macro">unimplemented!</span>(<span class="string">"getchar"</span>);
}
<span class="string">'[' </span>=> {
<span class="comment">// Create new label pair.
</span>label_stack.push((Label::new(), Label::new()));
<span class="comment">// UNWRAP: We just pushed a new entry on the stack.
</span><span class="kw">let </span>label_pair = label_stack.last_mut().unwrap();
<span class="comment">// Goto label_pair.0 if data memory at active cell is 0.
// if vm.dmem[vm.dptr] == 0 goto label_pair.0
</span>asm.cmp(
Mem8::indirect_base_index(dmem_base, dmem_idx),
Imm8::from(<span class="number">0u8</span>),
);
asm.jz(<span class="kw-2">&mut </span>label_pair.<span class="number">0</span>);
<span class="comment">// Bind label_pair.1 after the jump instruction, which will be
// the branch target for the matching ']'.
</span>asm.bind(<span class="kw-2">&mut </span>label_pair.<span class="number">1</span>);
}
<span class="string">']' </span>=> {
<span class="kw">let </span><span class="kw-2">mut </span>label_pair = label_stack
.pop()
.expect(<span class="string">"encountered un-balanced brackets, found ']' without matching '['"</span>);
<span class="comment">// Goto label_pair.1 if data memory at active cell is not 0.
// if vm.dmem[vm.dptr] != 0 goto label_pair.1
</span>asm.cmp(
Mem8::indirect_base_index(dmem_base, dmem_idx),
Imm8::from(<span class="number">0u8</span>),
);
asm.jnz(<span class="kw-2">&mut </span>label_pair.<span class="number">1</span>);
<span class="comment">// Bind label_pair.0 after the jump instruction, which is the
// branch target for the matching '['.
</span>asm.bind(<span class="kw-2">&mut </span>label_pair.<span class="number">0</span>);
}
<span class="kw">_ </span>=> <span class="macro">unreachable!</span>(),
}
<span class="comment">// Increment pc to next instruction.
</span>pc += <span class="number">1</span>;
}
<span class="kw">let </span><span class="kw-2">mut </span>epilogue = Label::new();
<span class="comment">// Successful return from bf program.
</span>asm.xor(Reg64::rax, Reg64::rax);
asm.bind(<span class="kw-2">&mut </span>epilogue);
<span class="comment">// Restore callee saved registers before returning from jit.
</span>asm.pop(dmem_idx);
asm.pop(dmem_size);
asm.pop(dmem_base);
asm.ret();
<span class="comment">// Return because of data pointer overflow.
</span>asm.bind(<span class="kw-2">&mut </span>oob_ov);
asm.mov(Reg64::rax, Imm64::from(<span class="number">1</span>));
asm.jmp(<span class="kw-2">&mut </span>epilogue);
<span class="comment">// Return because of data pointer underflow.
</span>asm.bind(<span class="kw-2">&mut </span>oob_uv);
asm.mov(Reg64::rax, Imm64::from(<span class="number">2</span>));
asm.jmp(<span class="kw-2">&mut </span>epilogue);
<span class="kw">if </span>!label_stack.is_empty() {
<span class="macro">panic!</span>(<span class="string">"encountered un-balanced brackets, left-over '[' after jitting bf program"</span>)
}
<span class="comment">// Get function pointer to jitted bf program.
</span><span class="kw">let </span><span class="kw-2">mut </span>rt = Runtime::new();
<span class="kw">let </span>bf_entry = <span class="kw">unsafe </span>{ rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>(<span class="kw-2">*mut </span>u8) -> u64>(asm.into_code()) };
<span class="comment">// Execute jitted bf program.
</span><span class="kw">match </span>bf_entry(<span class="kw-2">&mut </span>vm.dmem <span class="kw">as </span><span class="kw-2">*mut </span>u8) {
<span class="number">0 </span>=> { <span class="comment">/* success */ </span>}
<span class="number">1 </span>=> <span class="macro">panic!</span>(<span class="string">"oob: data pointer overflow"</span>),
<span class="number">2 </span>=> <span class="macro">panic!</span>(<span class="string">"oob: data pointer underflow"</span>),
<span class="kw">_ </span>=> <span class="macro">unreachable!</span>(),
}
}
<span class="comment">// -- MAIN ---------------------------------------------------------------------
</span><span class="kw">fn </span>main() {
<span class="comment">// https://en.wikipedia.org/wiki/Brainfuck#Hello_World!
</span><span class="kw">let </span>inp = <span class="string">"++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++."</span>;
<span class="macro">println!</span>(<span class="string">"hello-world (wikipedia.org) - interp"</span>);
run_interp(inp);
<span class="macro">println!</span>(<span class="string">"hello-world (wikipedia.org) - jit"</span>);
run_jit(inp);
<span class="comment">// https://programmingwiki.de/Brainfuck
</span><span class="kw">let </span>inp = <span class="string">">+++++++++[<++++++++>-]<.>+++++++[<++++>-]<+.+++++++..+++.[-]>++++++++[<++++>-] <.>+++++++++++[<++++++++>-]<-.--------.+++.------.--------.[-]>++++++++[<++++>- ]<+.[-]++++++++++."</span>;
<span class="macro">println!</span>(<span class="string">"hello-world (programmingwiki.de) - interp"</span>);
run_interp(inp);
<span class="macro">println!</span>(<span class="string">"hello-world (programmingwiki.de) - jit"</span>);
run_jit(inp);
}
<span class="attr">#[cfg(test)]
</span><span class="kw">mod </span>test {
<span class="kw">use super</span>::<span class="kw-2">*</span>;
<span class="attr">#[test]
</span><span class="kw">fn </span>data_ptr_no_overflow() {
<span class="kw">let </span>inp = std::iter::repeat(<span class="string">'>'</span>).take(<span class="number">255</span>).collect::<String>();
run_jit(<span class="kw-2">&</span>inp);
}
<span class="attr">#[test]
#[should_panic]
</span><span class="kw">fn </span>data_ptr_overflow() {
<span class="kw">let </span>inp = std::iter::repeat(<span class="string">'>'</span>).take(<span class="number">255 </span>+ <span class="number">1</span>).collect::<String>();
run_jit(<span class="kw-2">&</span>inp);
}
<span class="attr">#[test]
</span><span class="kw">fn </span>data_ptr_no_underflow() {
<span class="kw">let </span>inp = <span class="string">">><< ><"</span>;
run_jit(inp);
}
<span class="attr">#[test]
#[should_panic]
</span><span class="kw">fn </span>data_ptr_underflow() {
<span class="kw">let </span>inp = <span class="string">">><< >< <"</span>;
run_jit(<span class="kw-2">&</span>inp);
}
}
</code></pre></div></section></main></body></html>
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