use juicebox_asm::prelude::*; use juicebox_asm::rt::Runtime; const fn fib_rs(n: u64) -> u64 { match n { 0 => 0, 1 => 1, _ => fib_rs(n - 2) + fib_rs(n - 1), } } fn main() { let mut asm = Asm::new(); let mut lp = Label::new(); let mut end = Label::new(); // Reference implementation: // // int fib(int n) { // int tmp = 0; // int prv = 1; // int sum = 0; // loop: // if (n == 0) goto end; // tmp = sum; // sum += prv; // prv = tmp; // --n; // goto loop; // end: // return sum; // } // SystemV abi: // rdi -> first argument // rax -> return value let n = Reg64::rdi; let sum = Reg64::rax; let tmp = Reg64::rcx; let prv = Reg64::rbx; asm.mov(tmp, Imm64::from(0)); asm.mov(prv, Imm64::from(1)); asm.mov(sum, Imm64::from(0)); asm.bind(&mut lp); asm.test(n, n); asm.jz(&mut end); asm.mov(tmp, sum); asm.add(sum, prv); asm.mov(prv, tmp); asm.dec(n); asm.jmp(&mut lp); asm.bind(&mut end); asm.ret(); // Write out JIT code for visualization. // Disassemble for example with `ndisasm -b 64 jit.asm`. let code = asm.into_code(); std::fs::write("jit.asm", &code).unwrap(); // Move code into executable page and get function pointer to it. let rt = Runtime::new(&code); let fib = unsafe { rt.as_fn:: u64>() }; for n in 0..15 { let fib_jit = fib(n); println!("fib({}) = {}", n, fib_jit); assert_eq!(fib_jit, fib_rs(n)); } }