edg-l/edlang
1
1
Fork 0
mirror of https://github.com/edg-l/edlang.git synced 2024-11-15 12:38:23 +00:00
Code Issues Packages Projects Releases Wiki Activity
edlang/regex_syntax/utf8/index.html
edg-l 5c4cbb28c1 deploy: 4a83cfd6f9
2024-02-13 06:38:44 +00:00

60 lines
8.6 KiB
HTML
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

<!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="Converts ranges of Unicode scalar values to equivalent ranges of UTF-8 bytes."><title>regex_syntax::utf8 - Rust</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/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><link rel="stylesheet" href="../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../static.files/rustdoc-ac92e1bbe349e143.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="regex_syntax" data-themes="" data-resource-suffix="" data-rustdoc-version="1.76.0 (07dca489a 2024-02-04)" data-channel="1.76.0" data-search-js="search-2b6ce74ff89ae146.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../static.files/storage-f2adc0d6ca4d09fb.js"></script><script defer src="../sidebar-items.js"></script><script defer src="../../static.files/main-305769736d49e732.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-feafe1bb7466e4bd.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 mod"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">&#9776;</button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../regex_syntax/index.html">regex_syntax</a><span class="version">0.8.2</span></h2></div><h2 class="location"><a href="#">Module utf8</a></h2><div class="sidebar-elems"><section><ul class="block"><li><a href="#structs">Structs</a></li><li><a href="#enums">Enums</a></li></ul></section><h2><a href="../index.html">In crate regex_syntax</a></h2></div></nav><div class="sidebar-resizer"></div>
<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../../regex_syntax/all.html" title="show sidebar"></a></div><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" tabindex="-1"><a href="../../help.html" title="help">?</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="main-heading"><h1>Module <a href="../index.html">regex_syntax</a>::<wbr><a class="mod" href="#">utf8</a><button id="copy-path" title="Copy item path to clipboard"><img src="../../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../../src/regex_syntax/utf8.rs.html#1-592">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>&#x2212;</span>]</button></span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Converts ranges of Unicode scalar values to equivalent ranges of UTF-8 bytes.</p>
<p>This is sub-module is useful for constructing byte based automatons that need
to embed UTF-8 decoding. The most common use of this module is in conjunction
with the <a href="../hir/struct.ClassUnicodeRange.html" title="struct regex_syntax::hir::ClassUnicodeRange"><code>hir::ClassUnicodeRange</code></a> type.</p>
<p>See the documentation on the <code>Utf8Sequences</code> iterator for more details and
an example.</p>
<h2 id="wait-what-is-this"><a href="#wait-what-is-this">Wait, what is this?</a></h2>
<p>This is simplest to explain with an example. Let’s say you wanted to test
whether a particular byte sequence was a Cyrillic character. One possible
scalar value range is <code>[0400-04FF]</code>. The set of allowed bytes for this
range can be expressed as a sequence of byte ranges:</p>
<div class="example-wrap"><pre class="language-text"><code>[D0-D3][80-BF]
</code></pre></div>
<p>This is simple enough: simply encode the boundaries, <code>0400</code> encodes to
<code>D0 80</code> and <code>04FF</code> encodes to <code>D3 BF</code>, and create ranges from each
corresponding pair of bytes: <code>D0</code> to <code>D3</code> and <code>80</code> to <code>BF</code>.</p>
<p>However, what if you wanted to add the Cyrillic Supplementary characters to
your range? Your range might then become <code>[0400-052F]</code>. The same procedure
as above doesn’t quite work because <code>052F</code> encodes to <code>D4 AF</code>. The byte ranges
you’d get from the previous transformation would be <code>[D0-D4][80-AF]</code>. However,
this isn’t quite correct because this range doesn’t capture many characters,
for example, <code>04FF</code> (because its last byte, <code>BF</code> isn’t in the range <code>80-AF</code>).</p>
<p>Instead, you need multiple sequences of byte ranges:</p>
<div class="example-wrap"><pre class="language-text"><code>[D0-D3][80-BF] # matches codepoints 0400-04FF
[D4][80-AF] # matches codepoints 0500-052F
</code></pre></div>
<p>This gets even more complicated if you want bigger ranges, particularly if
they naively contain surrogate codepoints. For example, the sequence of byte
ranges for the basic multilingual plane (<code>[0000-FFFF]</code>) look like this:</p>
<div class="example-wrap"><pre class="language-text"><code>[0-7F]
[C2-DF][80-BF]
[E0][A0-BF][80-BF]
[E1-EC][80-BF][80-BF]
[ED][80-9F][80-BF]
[EE-EF][80-BF][80-BF]
</code></pre></div>
<p>Note that the byte ranges above will <em>not</em> match any erroneous encoding of
UTF-8, including encodings of surrogate codepoints.</p>
<p>And, of course, for all of Unicode (<code>[000000-10FFFF]</code>):</p>
<div class="example-wrap"><pre class="language-text"><code>[0-7F]
[C2-DF][80-BF]
[E0][A0-BF][80-BF]
[E1-EC][80-BF][80-BF]
[ED][80-9F][80-BF]
[EE-EF][80-BF][80-BF]
[F0][90-BF][80-BF][80-BF]
[F1-F3][80-BF][80-BF][80-BF]
[F4][80-8F][80-BF][80-BF]
</code></pre></div>
<p>This module automates the process of creating these byte ranges from ranges of
Unicode scalar values.</p>
<h2 id="lineage"><a href="#lineage">Lineage</a></h2>
<p>I got the idea and general implementation strategy from Russ Cox in his
<a href="https://web.archive.org/web/20160404141123/https://swtch.com/~rsc/regexp/regexp3.html">article on regexps</a> and RE2.
Russ Cox got it from Ken Thompson’s <code>grep</code> (no source, folk lore?).
I also got the idea from
<a href="https://github.com/apache/lucene-solr/blob/ae93f4e7ac6a3908046391de35d4f50a0d3c59ca/lucene/core/src/java/org/apache/lucene/util/automaton/UTF32ToUTF8.java">Lucene</a>,
which uses it for executing automata on their term index.</p>
</div></details><h2 id="structs" class="section-header"><a href="#structs">Structs</a></h2><ul class="item-table"><li><div class="item-name"><a class="struct" href="struct.Utf8Range.html" title="struct regex_syntax::utf8::Utf8Range">Utf8Range</a></div><div class="desc docblock-short">A single inclusive range of UTF-8 bytes.</div></li><li><div class="item-name"><a class="struct" href="struct.Utf8Sequences.html" title="struct regex_syntax::utf8::Utf8Sequences">Utf8Sequences</a></div><div class="desc docblock-short">An iterator over ranges of matching UTF-8 byte sequences.</div></li></ul><h2 id="enums" class="section-header"><a href="#enums">Enums</a></h2><ul class="item-table"><li><div class="item-name"><a class="enum" href="enum.Utf8Sequence.html" title="enum regex_syntax::utf8::Utf8Sequence">Utf8Sequence</a></div><div class="desc docblock-short">Utf8Sequence represents a sequence of byte ranges.</div></li></ul></section></div></main></body></html>
Reference in a new issue View git blame Copy permalink