visus
/
toolchain-gcc-arm-embedded


			
							<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Copyright (C) 1988-2020 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 6.5, http://www.gnu.org/software/texinfo/ -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Properties of the poly_int comparisons (GNU Compiler Collection (GCC) Internals)</title>

<meta name="description" content="Properties of the poly_int comparisons (GNU Compiler Collection (GCC) Internals)">
<meta name="keywords" content="Properties of the poly_int comparisons (GNU Compiler Collection (GCC) Internals)">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<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="Comparisons-involving-poly_005fint.html#Comparisons-involving-poly_005fint" rel="up" title="Comparisons involving poly_int">
<link href="Comparing-potentially_002dunordered-poly_005fints.html#Comparing-potentially_002dunordered-poly_005fints" rel="next" title="Comparing potentially-unordered poly_ints">
<link href="Comparison-functions-for-poly_005fint.html#Comparison-functions-for-poly_005fint" rel="prev" title="Comparison functions for poly_int">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
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.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en">
<a name="Properties-of-the-poly_005fint-comparisons"></a>
<div class="header">
<p>
Next: <a href="Comparing-potentially_002dunordered-poly_005fints.html#Comparing-potentially_002dunordered-poly_005fints" accesskey="n" rel="next">Comparing potentially-unordered <code>poly_int</code>s</a>, Previous: <a href="Comparison-functions-for-poly_005fint.html#Comparison-functions-for-poly_005fint" accesskey="p" rel="prev">Comparison functions for <code>poly_int</code></a>, Up: <a href="Comparisons-involving-poly_005fint.html#Comparisons-involving-poly_005fint" accesskey="u" rel="up">Comparisons involving <code>poly_int</code></a> &nbsp; [<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="Properties-of-the-poly_005fint-comparisons-1"></a>
<h4 class="subsection">10.3.2 Properties of the <code>poly_int</code> comparisons</h4>

<p>All &ldquo;maybe&rdquo; relations except <code>maybe_ne</code> are transitive, so for example:
</p>
<div class="smallexample">
<pre class="smallexample">maybe_lt (<var>a</var>, <var>b</var>) &amp;&amp; maybe_lt (<var>b</var>, <var>c</var>) implies maybe_lt (<var>a</var>, <var>c</var>)
</pre></div>

<p>for all <var>a</var>, <var>b</var> and <var>c</var>.  <code>maybe_lt</code>, <code>maybe_gt</code>
and <code>maybe_ne</code> are irreflexive, so for example:
</p>
<div class="smallexample">
<pre class="smallexample">!maybe_lt (<var>a</var>, <var>a</var>)
</pre></div>

<p>is true for all <var>a</var>.  <code>maybe_le</code>, <code>maybe_eq</code> and <code>maybe_ge</code>
are reflexive, so for example:
</p>
<div class="smallexample">
<pre class="smallexample">maybe_le (<var>a</var>, <var>a</var>)
</pre></div>

<p>is true for all <var>a</var>.  <code>maybe_eq</code> and <code>maybe_ne</code> are symmetric, so:
</p>
<div class="smallexample">
<pre class="smallexample">maybe_eq (<var>a</var>, <var>b</var>) == maybe_eq (<var>b</var>, <var>a</var>)
maybe_ne (<var>a</var>, <var>b</var>) == maybe_ne (<var>b</var>, <var>a</var>)
</pre></div>

<p>for all <var>a</var> and <var>b</var>.  In addition:
</p>
<div class="smallexample">
<pre class="smallexample">maybe_le (<var>a</var>, <var>b</var>) == maybe_lt (<var>a</var>, <var>b</var>) || maybe_eq (<var>a</var>, <var>b</var>)
maybe_ge (<var>a</var>, <var>b</var>) == maybe_gt (<var>a</var>, <var>b</var>) || maybe_eq (<var>a</var>, <var>b</var>)
maybe_lt (<var>a</var>, <var>b</var>) == maybe_gt (<var>b</var>, <var>a</var>)
maybe_le (<var>a</var>, <var>b</var>) == maybe_ge (<var>b</var>, <var>a</var>)
</pre></div>

<p>However:
</p>
<div class="smallexample">
<pre class="smallexample">maybe_le (<var>a</var>, <var>b</var>) &amp;&amp; maybe_le (<var>b</var>, <var>a</var>) does not imply !maybe_ne (<var>a</var>, <var>b</var>) [== known_eq (<var>a</var>, <var>b</var>)]
maybe_ge (<var>a</var>, <var>b</var>) &amp;&amp; maybe_ge (<var>b</var>, <var>a</var>) does not imply !maybe_ne (<var>a</var>, <var>b</var>) [== known_eq (<var>a</var>, <var>b</var>)]
</pre></div>

<p>One example is again &lsquo;<samp><var>a</var> == 3 + 4<var>x</var></samp>&rsquo;
and &lsquo;<samp><var>b</var> == 1 + 5<var>x</var></samp>&rsquo;, where &lsquo;<samp>maybe_le (<var>a</var>, <var>b</var>)</samp>&rsquo;,
&lsquo;<samp>maybe_ge (<var>a</var>, <var>b</var>)</samp>&rsquo; and &lsquo;<samp>maybe_ne (<var>a</var>, <var>b</var>)</samp>&rsquo;
all hold.  <code>maybe_le</code> and <code>maybe_ge</code> are therefore not antisymetric
and do not form a partial order.
</p>
<p>From the above, it follows that:
</p>
<ul>
<li> All &ldquo;known&rdquo; relations except <code>known_ne</code> are transitive.

</li><li> <code>known_lt</code>, <code>known_ne</code> and <code>known_gt</code> are irreflexive.

</li><li> <code>known_le</code>, <code>known_eq</code> and <code>known_ge</code> are reflexive.
</li></ul>

<p>Also:
</p>
<div class="smallexample">
<pre class="smallexample">known_lt (<var>a</var>, <var>b</var>) == known_gt (<var>b</var>, <var>a</var>)
known_le (<var>a</var>, <var>b</var>) == known_ge (<var>b</var>, <var>a</var>)
known_lt (<var>a</var>, <var>b</var>) implies !known_lt (<var>b</var>, <var>a</var>)  [asymmetry]
known_gt (<var>a</var>, <var>b</var>) implies !known_gt (<var>b</var>, <var>a</var>)
known_le (<var>a</var>, <var>b</var>) &amp;&amp; known_le (<var>b</var>, <var>a</var>) == known_eq (<var>a</var>, <var>b</var>) [== !maybe_ne (<var>a</var>, <var>b</var>)]
known_ge (<var>a</var>, <var>b</var>) &amp;&amp; known_ge (<var>b</var>, <var>a</var>) == known_eq (<var>a</var>, <var>b</var>) [== !maybe_ne (<var>a</var>, <var>b</var>)]
</pre></div>

<p><code>known_le</code> and <code>known_ge</code> are therefore antisymmetric and are
partial orders.  However:
</p>
<div class="smallexample">
<pre class="smallexample">known_le (<var>a</var>, <var>b</var>) does not imply known_lt (<var>a</var>, <var>b</var>) || known_eq (<var>a</var>, <var>b</var>)
known_ge (<var>a</var>, <var>b</var>) does not imply known_gt (<var>a</var>, <var>b</var>) || known_eq (<var>a</var>, <var>b</var>)
</pre></div>

<p>For example, &lsquo;<samp>known_le (4, 4 + 4<var>x</var>)</samp>&rsquo; holds because the runtime
indeterminate <var>x</var> is a nonnegative integer, but neither
<code>known_lt (4, 4 + 4<var>x</var>)</code> nor <code>known_eq (4, 4 + 4<var>x</var>)</code> hold.
</p>
<hr>
<div class="header">
<p>
Next: <a href="Comparing-potentially_002dunordered-poly_005fints.html#Comparing-potentially_002dunordered-poly_005fints" accesskey="n" rel="next">Comparing potentially-unordered <code>poly_int</code>s</a>, Previous: <a href="Comparison-functions-for-poly_005fint.html#Comparison-functions-for-poly_005fint" accesskey="p" rel="prev">Comparison functions for <code>poly_int</code></a>, Up: <a href="Comparisons-involving-poly_005fint.html#Comparisons-involving-poly_005fint" accesskey="u" rel="up">Comparisons involving <code>poly_int</code></a> &nbsp; [<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>