Boost C++ Libraries of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of boost. Click here for the latest Boost documentation.
C++ Boost

ct_gcd_lcm - Compile-Time GCD and LCM


detail/ct_gcd_lcm.hpp provides two compile-time algorithms: greatest common divisor and least common multiple.


namespace details {
namespace pool {

template <unsigned A, unsigned B>
struct ct_gcd
  static const unsigned value = ...;
template <unsigned A, unsigned B>
struct ct_lcm
  static const unsigned value = ...;

} // namespace pool
} // namespace details


Symbol Table
Symbol Meaning
A, B compile-time unsigned integer constants[5.19/1]

Expression Result Type Value Precondition
ct_gcd<A, B>::value compile-time unsigned integer constant The greatest common divisor of A and B A != 0 && B != 0
ct_lcm<A, B>::value compile-time unsigned integer constant The least common multiple of A and B A != 0 && B != 0


Since these are compile-time algorithms, violation of the preconditions will result in a compile-time error.


Selected Quotations from the Standard

5.19/1: Expressions: Constant Expressions: ". . . An integral constant expression can involve only literals (2.13), enumerators, const 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 sizeof 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 sizeof expressions, functions, class objects, pointers, or references shall not be used, and assignment, increment, decrement, function-call, or comma operators shall not be used."

Future Directions

This header may be replaced by a Boost compile-time algorithms library.

Valid HTML 4.01 Transitional

Revised 05 December, 2006

Copyright © 2000, 2001 Stephen Cleary (scleary AT jerviswebb DOT com)

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at