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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) | |
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diff --git a/share/doc/gfortran/UNION-and-MAP.html b/share/doc/gfortran/UNION-and-MAP.html new file mode 100644 index 0000000..c7e9e8d --- /dev/null +++ b/share/doc/gfortran/UNION-and-MAP.html @@ -0,0 +1,193 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1999-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". + +(a) The FSF's Front-Cover Text is: + +A GNU Manual + +(b) The FSF's Back-Cover Text is: + +You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>The GNU Fortran Compiler: UNION and MAP</title> + +<meta name="description" content="The GNU Fortran Compiler: UNION and MAP"> +<meta name="keywords" content="The GNU Fortran Compiler: UNION and MAP"> +<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="Option-Index.html#Option-Index" rel="index" title="Option Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" rel="up" title="Extensions implemented in GNU Fortran"> +<link href="Type-variants-for-integer-intrinsics.html#Type-variants-for-integer-intrinsics" rel="next" title="Type variants for integer intrinsics"> +<link href="STRUCTURE-and-RECORD.html#STRUCTURE-and-RECORD" rel="previous" title="STRUCTURE and RECORD"> +<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="UNION-and-MAP"></a> +<div class="header"> +<p> +Next: <a href="Type-variants-for-integer-intrinsics.html#Type-variants-for-integer-intrinsics" accesskey="n" rel="next">Type variants for integer intrinsics</a>, Previous: <a href="STRUCTURE-and-RECORD.html#STRUCTURE-and-RECORD" accesskey="p" rel="previous">STRUCTURE and RECORD</a>, Up: <a href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" accesskey="u" rel="up">Extensions implemented in GNU Fortran</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="UNION-and-MAP-1"></a> +<h4 class="subsection">5.1.23 <code>UNION</code> and <code>MAP</code></h4> +<a name="index-UNION"></a> +<a name="index-MAP"></a> + +<p>Unions are an old vendor extension which were commonly used with the +non-standard <a href="STRUCTURE-and-RECORD.html#STRUCTURE-and-RECORD">STRUCTURE and RECORD</a> extensions. Use of <code>UNION</code> and +<code>MAP</code> is automatically enabled with <samp>-fdec-structure</samp>. +</p> +<p>A <code>UNION</code> declaration occurs within a structure; within the definition of +each union is a number of <code>MAP</code> blocks. Each <code>MAP</code> shares storage +with its sibling maps (in the same union), and the size of the union is the +size of the largest map within it, just as with unions in C. The major +difference is that component references do not indicate which union or map the +component is in (the compiler gets to figure that out). +</p> +<p>Here is a small example: +</p><div class="smallexample"> +<pre class="smallexample">structure /myunion/ +union + map + character(2) w0, w1, w2 + end map + map + character(6) long + end map +end union +end structure + +record /myunion/ rec +! After this assignment... +rec.long = 'hello!' + +! The following is true: +! rec.w0 === 'he' +! rec.w1 === 'll' +! rec.w2 === 'o!' +</pre></div> + +<p>The two maps share memory, and the size of the union is ultimately six bytes: +</p> +<div class="example"> +<pre class="example">0 1 2 3 4 5 6 Byte offset +------------------------------- +| | | | | | | +------------------------------- + +^ W0 ^ W1 ^ W2 ^ + \-------/ \-------/ \-------/ + +^ LONG ^ + \---------------------------/ +</pre></div> + +<p>Following is an example mirroring the layout of an Intel x86_64 register: +</p> +<div class="example"> +<pre class="example">structure /reg/ + union ! U0 ! rax + map + character(16) rx + end map + map + character(8) rh ! rah + union ! U1 + map + character(8) rl ! ral + end map + map + character(8) ex ! eax + end map + map + character(4) eh ! eah + union ! U2 + map + character(4) el ! eal + end map + map + character(4) x ! ax + end map + map + character(2) h ! ah + character(2) l ! al + end map + end union + end map + end union + end map + end union +end structure +record /reg/ a + +! After this assignment... +a.rx = 'AAAAAAAA.BBB.C.D' + +! The following is true: +a.rx === 'AAAAAAAA.BBB.C.D' +a.rh === 'AAAAAAAA' +a.rl === '.BBB.C.D' +a.ex === '.BBB.C.D' +a.eh === '.BBB' +a.el === '.C.D' +a.x === '.C.D' +a.h === '.C' +a.l === '.D' +</pre></div> + +<hr> +<div class="header"> +<p> +Next: <a href="Type-variants-for-integer-intrinsics.html#Type-variants-for-integer-intrinsics" accesskey="n" rel="next">Type variants for integer intrinsics</a>, Previous: <a href="STRUCTURE-and-RECORD.html#STRUCTURE-and-RECORD" accesskey="p" rel="previous">STRUCTURE and RECORD</a>, Up: <a href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" accesskey="u" rel="up">Extensions implemented in GNU Fortran</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |