source: NonGTP/Boost/boost/pool/detail/ct_gcd_lcm.hpp @ 857

Revision 857, 2.5 KB checked in by igarcia, 19 years ago (diff)
Line 
1// Copyright (C) 2000 Stephen Cleary
2//
3// Distributed under the Boost Software License, Version 1.0. (See
4// accompanying file LICENSE_1_0.txt or copy at
5// http://www.boost.org/LICENSE_1_0.txt)
6//
7// See http://www.boost.org for updates, documentation, and revision history.
8
9#ifndef BOOST_POOL_CT_GCD_LCM_HPP
10#define BOOST_POOL_CT_GCD_LCM_HPP
11
12#include <boost/static_assert.hpp>
13#include <boost/type_traits/ice.hpp>
14
15namespace boost {
16
17namespace details {
18namespace pool {
19
20// Compile-time calculation of greatest common divisor and least common multiple
21
22//
23// ct_gcd is a compile-time algorithm that calculates the greatest common
24//  divisor of two unsigned integers, using Euclid's algorithm.
25//
26// assumes: A != 0 && B != 0
27//
28
29#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
30
31namespace details {
32template <unsigned A, unsigned B, bool Bis0>
33struct ct_gcd_helper;
34template <unsigned A, unsigned B>
35struct ct_gcd_helper<A, B, false>
36{
37  BOOST_STATIC_CONSTANT(unsigned, A_mod_B_ = A % B);
38  BOOST_STATIC_CONSTANT(unsigned, value =
39      (::boost::details::pool::details::ct_gcd_helper<
40        B, static_cast<unsigned>(A_mod_B_),
41        ::boost::type_traits::ice_eq<A_mod_B_, 0>::value
42        >::value) );
43};
44template <unsigned A, unsigned B>
45struct ct_gcd_helper<A, B, true>
46{
47  BOOST_STATIC_CONSTANT(unsigned, value = A);
48};
49} // namespace details
50
51template <unsigned A, unsigned B>
52struct ct_gcd
53{
54  BOOST_STATIC_ASSERT(A != 0 && B != 0);
55  BOOST_STATIC_CONSTANT(unsigned, value =
56      (::boost::details::pool::details::ct_gcd_helper<A, B, false>::value) );
57};
58
59#else
60
61// Thanks to Peter Dimov for providing this workaround!
62namespace details {
63template<unsigned A> struct ct_gcd2
64{
65  template<unsigned B>
66  struct helper
67  {
68    BOOST_STATIC_CONSTANT(unsigned, value = ct_gcd2<B>::helper<A % B>::value);
69  };
70  template<>
71  struct helper<0>
72  {
73    BOOST_STATIC_CONSTANT(unsigned, value = A);
74  };
75};
76} // namespace details
77
78template<unsigned A, unsigned B> struct ct_gcd
79{
80  BOOST_STATIC_ASSERT(A != 0 && B != 0);
81  enum { value = details::ct_gcd2<A>::helper<B>::value };
82};
83
84#endif
85
86//
87// ct_lcm is a compile-time algorithm that calculates the least common
88//  multiple of two unsigned integers.
89//
90// assumes: A != 0 && B != 0
91//
92template <unsigned A, unsigned B>
93struct ct_lcm
94{
95  BOOST_STATIC_CONSTANT(unsigned, value =
96      (A / ::boost::details::pool::ct_gcd<A, B>::value * B) );
97};
98
99} // namespace pool
100} // namespace details
101
102} // namespace boost
103
104#endif
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