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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><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="fib" 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">fib/</div>fib.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="#77" id="77">77</a></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) -&gt; u64 {
    <span class="kw">match </span>n {
        <span class="number">0 </span>=&gt; <span class="number">0</span>,
        <span class="number">1 </span>=&gt; <span class="number">1</span>,
        <span class="kw">_ </span>=&gt; 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 -&gt; first argument
    //   rax -&gt; 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::rdx;

    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">&amp;mut </span>lp);
    asm.test(n, n);
    asm.jz(<span class="kw-2">&amp;mut </span>end);
    asm.mov(tmp, sum);
    asm.add(sum, prv);
    asm.mov(prv, tmp);
    asm.dec(n);
    asm.jmp(<span class="kw-2">&amp;mut </span>lp);
    asm.bind(<span class="kw-2">&amp;mut </span>end);
    asm.ret();

    <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::&lt;<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>(u64) -&gt; u64&gt;(asm.into_code()) };

    <span class="comment">// Disassemble JIT code and write to stdout.
    </span>rt.disasm();

    <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));
    }
}
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