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Brainfuck VM. +//! +//! This example implements a simple +//! [brainfuck](https://en.wikipedia.org/wiki/Brainfuck) 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. + +</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, MemOp, MemOp8, Reg64, Reg8}; + +<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 target. + </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_idx = Reg64::r12; + + <span class="kw">let </span><span class="kw-2">mut </span>asm = Asm::new(); + <span class="comment">// Move data memory pointer (argument on jit entry) into correct + // register. + </span>asm.mov(dmem_base, Reg64::rdi); + <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">// Generate code for each instruction in the bf program. + </span><span class="kw">for </span>insn <span class="kw">in </span>vm.imem { + <span class="kw">match </span>insn { + <span class="string">'>' </span>=> { + <span class="comment">// TODO: generate runtime bounds check. + </span>asm.inc(dmem_idx); + } + <span class="string">'<' </span>=> { + <span class="comment">// TODO: generate runtime bounds check. + </span>asm.dec(dmem_idx); + } + <span class="string">'+' </span>=> { + asm.inc(MemOp8::from(MemOp::IndirectBaseIndex(dmem_base, dmem_idx))); + } + <span class="string">'-' </span>=> { + asm.dec(MemOp8::from(MemOp::IndirectBaseIndex(dmem_base, dmem_idx))); + } + <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, MemOp::IndirectBaseIndex(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( + MemOp::IndirectBaseIndex(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( + MemOp::IndirectBaseIndex(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">// Return from bf program. + </span>asm.ret(); + + <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">// Execute 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)>(asm.into_code()) }; + bf_entry(<span class="kw-2">&mut </span>vm.dmem <span class="kw">as </span><span class="kw-2">*mut </span>u8); +} + +<span class="kw">fn </span>main() { + <span class="comment">// https://en.wikipedia.org/wiki/Brainfuck#Adding_two_values + //let inp = "++>+++++ [<+>-] ++++++++[<++++++>-]<."; + //println!("add-print-7 (wikipedia.org) - interp"); + //run_interp(inp); + //println!("add-print-7 (wikipedia.org) - jit"); + //run_jit(inp); + + // 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); +} +</code></pre></div></section></main></body></html>
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