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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/cppinternals/Hash-Nodes.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
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diff --git a/share/doc/cppinternals/Hash-Nodes.html b/share/doc/cppinternals/Hash-Nodes.html new file mode 100644 index 0000000..2d1f2a2 --- /dev/null +++ b/share/doc/cppinternals/Hash-Nodes.html @@ -0,0 +1,130 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>The GNU C Preprocessor Internals: Hash Nodes</title> + +<meta name="description" content="The GNU C Preprocessor Internals: Hash Nodes"> +<meta name="keywords" content="The GNU C Preprocessor Internals: Hash Nodes"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="index.html#Top" rel="up" title="Top"> +<link href="Macro-Expansion.html#Macro-Expansion" rel="next" title="Macro Expansion"> +<link href="Lexer.html#Lexer" rel="previous" title="Lexer"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Hash-Nodes"></a> +<div class="header"> +<p> +Next: <a href="Macro-Expansion.html#Macro-Expansion" accesskey="n" rel="next">Macro Expansion</a>, Previous: <a href="Lexer.html#Lexer" accesskey="p" rel="previous">Lexer</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Hash-Nodes-1"></a> +<h2 class="unnumbered">Hash Nodes</h2> +<a name="index-hash-table"></a> +<a name="index-identifiers"></a> +<a name="index-macros"></a> +<a name="index-assertions"></a> +<a name="index-named-operators"></a> + +<p>When cpplib encounters an “identifier”, it generates a hash code for +it and stores it in the hash table. By “identifier” we mean tokens +with type <code>CPP_NAME</code>; this includes identifiers in the usual C +sense, as well as keywords, directive names, macro names and so on. For +example, all of <code>pragma</code>, <code>int</code>, <code>foo</code> and +<code>__GNUC__</code> are identifiers and hashed when lexed. +</p> +<p>Each node in the hash table contain various information about the +identifier it represents. For example, its length and type. At any one +time, each identifier falls into exactly one of three categories: +</p> +<ul> +<li> Macros + +<p>These have been declared to be macros, either on the command line or +with <code>#define</code>. A few, such as <code>__TIME__</code> are built-ins +entered in the hash table during initialization. The hash node for a +normal macro points to a structure with more information about the +macro, such as whether it is function-like, how many arguments it takes, +and its expansion. Built-in macros are flagged as special, and instead +contain an enum indicating which of the various built-in macros it is. +</p> +</li><li> Assertions + +<p>Assertions are in a separate namespace to macros. To enforce this, cpp +actually prepends a <code>#</code> character before hashing and entering it in +the hash table. An assertion’s node points to a chain of answers to +that assertion. +</p> +</li><li> Void + +<p>Everything else falls into this category—an identifier that is not +currently a macro, or a macro that has since been undefined with +<code>#undef</code>. +</p> +<p>When preprocessing C++, this category also includes the named operators, +such as <code>xor</code>. In expressions these behave like the operators they +represent, but in contexts where the spelling of a token matters they +are spelt differently. This spelling distinction is relevant when they +are operands of the stringizing and pasting macro operators <code>#</code> and +<code>##</code>. Named operator hash nodes are flagged, both to catch the +spelling distinction and to prevent them from being defined as macros. +</p></li></ul> + +<p>The same identifiers share the same hash node. Since each identifier +token, after lexing, contains a pointer to its hash node, this is used +to provide rapid lookup of various information. For example, when +parsing a <code>#define</code> statement, CPP flags each argument’s identifier +hash node with the index of that argument. This makes duplicated +argument checking an O(1) operation for each argument. Similarly, for +each identifier in the macro’s expansion, lookup to see if it is an +argument, and which argument it is, is also an O(1) operation. Further, +each directive name, such as <code>endif</code>, has an associated directive +enum stored in its hash node, so that directive lookup is also O(1). +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Macro-Expansion.html#Macro-Expansion" accesskey="n" rel="next">Macro Expansion</a>, Previous: <a href="Lexer.html#Lexer" accesskey="p" rel="previous">Lexer</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |