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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/fib.rs`."><title>fib.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceSerif4-Bold-a2c9cd1067f8b328.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><link rel="stylesheet" href="../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../static.files/rustdoc-fa3bb1812debf86c.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="fib" data-themes="" data-resource-suffix="" data-rustdoc-version="1.74.0 (79e9716c9 2023-11-13)" data-channel="1.74.0" data-search-js="search-8be46b629f5f14a8.js" data-settings-js="settings-74424d7eec62a23e.js" ><script src="../../static.files/storage-fec3eaa3851e447d.js"></script><script defer src="../../static.files/src-script-3280b574d94e47b4.js"></script><script defer src="../../src-files.js"></script><script defer src="../../static.files/main-c5bd66d33317d69f.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-5d8b3c7633ad77ba.css"></noscript><link rel="alternate icon" type="image/png" href="../../static.files/favicon-16x16-8b506e7a72182f1c.png"><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"></nav><main><nav class="sub"><a class="sub-logo-container" href="../../fib/index.html"><img class="rust-logo" src="../../static.files/rust-logo-151179464ae7ed46.svg" alt="logo"></a><form class="search-form"><span></span><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><div data-nosnippet><pre class="src-line-numbers"><a href="#1" id="1">1</a>
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</pre></div><pre class="rust"><code><span class="doccomment">//! Fibonacci example.
//!
//! Jit compile a function at runtime (generate native host code) to compute the fibonacci sequence
//! to demonstrate the [`juicebox_asm`] crate.
</span><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, Label, Reg64};
<span class="kw">const fn </span>fib_rs(n: u64) -> u64 {
<span class="kw">match </span>n {
<span class="number">0 </span>=> <span class="number">0</span>,
<span class="number">1 </span>=> <span class="number">1</span>,
<span class="kw">_ </span>=> fib_rs(n - <span class="number">2</span>) + fib_rs(n - <span class="number">1</span>),
}
}
<span class="kw">fn </span>main() {
<span class="kw">let </span><span class="kw-2">mut </span>asm = Asm::new();
<span class="kw">let </span><span class="kw-2">mut </span>lp = Label::new();
<span class="kw">let </span><span class="kw-2">mut </span>end = Label::new();
<span class="comment">// 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
</span><span class="kw">let </span>n = Reg64::rdi;
<span class="kw">let </span>sum = Reg64::rax;
<span class="kw">let </span>tmp = Reg64::rcx;
<span class="kw">let </span>prv = Reg64::rbx;
asm.mov(tmp, Imm64::from(<span class="number">0</span>));
asm.mov(prv, Imm64::from(<span class="number">1</span>));
asm.mov(sum, Imm64::from(<span class="number">0</span>));
asm.bind(<span class="kw-2">&mut </span>lp);
asm.test(n, n);
asm.jz(<span class="kw-2">&mut </span>end);
asm.mov(tmp, sum);
asm.add(sum, prv);
asm.mov(prv, tmp);
asm.dec(n);
asm.jmp(<span class="kw-2">&mut </span>lp);
asm.bind(<span class="kw-2">&mut </span>end);
asm.ret();
<span class="comment">// Write out JIT code for visualization.
// Disassemble for example with `ndisasm -b 64 jit.asm`.
</span><span class="kw">let </span>code = asm.into_code();
std::fs::write(<span class="string">"jit.asm"</span>, <span class="kw-2">&</span>code).unwrap();
<span class="comment">// Move code into executable page and get function pointer to it.
</span><span class="kw">let </span><span class="kw-2">mut </span>rt = Runtime::new();
<span class="kw">let </span>fib = <span class="kw">unsafe </span>{ rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>(u64) -> u64>(code) };
<span class="kw">for </span>n <span class="kw">in </span><span class="number">0</span>..<span class="number">15 </span>{
<span class="kw">let </span>fib_jit = fib(n);
<span class="macro">println!</span>(<span class="string">"fib({}) = {}"</span>, n, fib_jit);
<span class="macro">assert_eq!</span>(fib_jit, fib_rs(n));
}
}
</code></pre></div></section></main></body></html>
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