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94 lines
3.5 KiB
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94 lines
3.5 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<TITLE>ct_gcd_lcm - Compile-Time GCD and LCM</TITLE>
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<LINK HREF="../pool.css" REL="stylesheet" TYPE="text/css">
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</HEAD>
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<BODY>
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<IMG SRC="../../../../boost.png" WIDTH=276 HEIGHT=86 ALT="C++ Boost">
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<H1 ALIGN=CENTER>ct_gcd_lcm - Compile-Time GCD and LCM</H1>
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<P>
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<H2>Introduction</H2>
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<P>
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detail/ct_gcd_lcm.hpp provides two compile-time algorithms: greatest common divisor and least common multiple.
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<P>
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<H2>Synopsis</H2>
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<PRE CLASS="code">namespace details {
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namespace pool {
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template <unsigned A, unsigned B>
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struct ct_gcd
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{
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static const unsigned value = ...;
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};
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template <unsigned A, unsigned B>
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struct ct_lcm
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{
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static const unsigned value = ...;
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};
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} // namespace pool
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} // namespace details</PRE>
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<P>
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<H2>Semantics</H2>
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<TABLE ALIGN=CENTER BORDER>
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<CAPTION><EM>Symbol Table</EM></CAPTION>
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<TR><TH>Symbol<TH>Meaning</TR>
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<TR><TD CLASS="code">A, B<TD>compile-time unsigned integer constants<A HREF="#5.19/1"><SUP>[5.19/1]</SUP></A></TR>
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</TABLE>
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<TABLE ALIGN=CENTER BORDER>
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<CAPTION><EM>Semantics</EM></CAPTION>
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<TR><TH>Expression<TH>Result Type<TH>Value<TH>Precondition
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<TR><TD CLASS="code">ct_gcd<A, B>::value<TD>compile-time unsigned integer constant<TD>The greatest common divisor of <SPAN CLASS="code">A</SPAN> and <SPAN CLASS="code">B</SPAN><TD CLASS="code">A != 0 && B != 0
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<TR><TD CLASS="code">ct_lcm<A, B>::value<TD>compile-time unsigned integer constant<TD>The least common multiple of <SPAN CLASS="code">A</SPAN> and <SPAN CLASS="code">B</SPAN><TD CLASS="code">A != 0 && B != 0
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</TABLE>
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<P>
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<H2>Notes</H2>
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<P>
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Since these are compile-time algorithms, violation of the preconditions will result in a compile-time error.
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<P>
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<H2>Dependencies</H2>
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<UL>
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<LI><boost/static_assert.hpp> (see <A HREF="../../../static_assert/static_assert.htm">Boost.Static_Assert</A>), to ensure preconditions are met.</LI>
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<LI><boost/type_traits/ice.hpp> (see <A HREF="../../../../more/int_const_guidelines.htm">Coding Guidelines for Integral Constant Expressions</A>), to help with portability.</LI>
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</UL>
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<P>
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<H2>Selected Quotations from the Standard</H2>
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<P>
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<A NAME="5.19/1">
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<STRONG>5.19/1: Expressions: Constant Expressions:</STRONG> ". . . An <EM>integral constant expression</EM> can involve only literals (2.13), enumerators, <SPAN CLASS="code">const</SPAN> variables or static data members of integral or enumeration types initialized with constant expressions (8.5), non-type template parameters of integral or enumeration types, and <SPAN CLASS="code">sizeof</SPAN> expressions. Floating literals (2.13.3) can appear only if they are cast to integral or enumeration types. Only type conversions to integral or enumeration types can be used. In particular, except in <SPAN CLASS="code">sizeof</SPAN> expressions, functions, class objects, pointers, or references shall not be used, and assignment, increment, decrement, function-call, or comma operators shall not be used."</A>
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<P>
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<H2>Future Directions</H2>
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<P>
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This header may be replaced by a Boost compile-time algorithms library.
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<P>
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<HR>
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<P>
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Copyright © 2000, 2001 Stephen Cleary (scleary AT jerviswebb DOT com)
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<P>
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This file can be redistributed and/or modified under the terms found in <A HREF="../copyright.html">copyright.html</A>
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<P>
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This software and its documentation is provided "as is" without express or implied warranty, and with no claim as to its suitability for any purpose.
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