| <!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 `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/unicode-normalization-0.1.22/src/perfect_hash.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>perfect_hash.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../normalize.css"><link rel="stylesheet" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../ayu.css" disabled><link rel="stylesheet" href="../../dark.css" disabled><link rel="stylesheet" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script defer src="../../source-script.js"></script><script defer src="../../source-files.js"></script><script defer src="../../main.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="icon" href="https://unicode-rs.github.io/unicode-rs_sm.png"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../unicode_normalization/index.html"><div class="logo-container"> |
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| </pre><pre class="rust"><code><span class="comment">// Copyright 2019 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| </span><span class="doccomment">//! Support for lookups based on minimal perfect hashing. |
| |
| </span><span class="comment">// This function is based on multiplication being fast and is "good enough". Also |
| // it can share some work between the unsalted and salted versions. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>my_hash(key: u32, salt: u32, n: usize) -> usize { |
| <span class="kw">let </span>y = key.wrapping_add(salt).wrapping_mul(<span class="number">2654435769</span>); |
| <span class="kw">let </span>y = y ^ key.wrapping_mul(<span class="number">0x31415926</span>); |
| (((y <span class="kw">as </span>u64) * (n <span class="kw">as </span>u64)) >> <span class="number">32</span>) <span class="kw">as </span>usize |
| } |
| |
| <span class="doccomment">/// Do a lookup using minimal perfect hashing. |
| /// |
| /// The table is stored as a sequence of "salt" values, then a sequence of |
| /// values that contain packed key/value pairs. The strategy is to hash twice. |
| /// The first hash retrieves a salt value that makes the second hash unique. |
| /// The hash function doesn't have to be very good, just good enough that the |
| /// resulting map is unique. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>mph_lookup<KV, V, FK, FV>( |
| x: u32, |
| salt: <span class="kw-2">&</span>[u16], |
| kv: <span class="kw-2">&</span>[KV], |
| fk: FK, |
| fv: FV, |
| default: V, |
| ) -> V |
| <span class="kw">where |
| </span>KV: Copy, |
| FK: Fn(KV) -> u32, |
| FV: Fn(KV) -> V, |
| { |
| <span class="kw">let </span>s = salt[my_hash(x, <span class="number">0</span>, salt.len())] <span class="kw">as </span>u32; |
| <span class="kw">let </span>key_val = kv[my_hash(x, s, salt.len())]; |
| <span class="kw">if </span>x == fk(key_val) { |
| fv(key_val) |
| } <span class="kw">else </span>{ |
| default |
| } |
| } |
| </code></pre></div> |
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