1 | /* boost random/detail/signed_unsigned_tools.hpp header file |
2 | * |
3 | * Copyright Jens Maurer 2006 |
4 | * Distributed under the Boost Software License, Version 1.0. (See |
5 | * accompanying file LICENSE_1_0.txt or copy at |
6 | * http://www.boost.org/LICENSE_1_0.txt) |
7 | * |
8 | * See http://www.boost.org for most recent version including documentation. |
9 | */ |
10 | |
11 | #ifndef BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_TOOLS |
12 | #define BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_TOOLS |
13 | |
14 | #include <boost/limits.hpp> |
15 | #include <boost/config.hpp> |
16 | #include <boost/random/traits.hpp> |
17 | |
18 | namespace boost { |
19 | namespace random { |
20 | namespace detail { |
21 | |
22 | |
23 | /* |
24 | * Compute x - y, we know that x >= y, return an unsigned value. |
25 | */ |
26 | |
27 | template<class T, bool sgn = std::numeric_limits<T>::is_signed && std::numeric_limits<T>::is_bounded> |
28 | struct subtract { }; |
29 | |
30 | template<class T> |
31 | struct subtract<T, /* signed */ false> |
32 | { |
33 | typedef T result_type; |
34 | result_type operator()(T x, T y) { return x - y; } |
35 | }; |
36 | |
37 | template<class T> |
38 | struct subtract<T, /* signed */ true> |
39 | { |
40 | typedef typename boost::random::traits::make_unsigned_or_unbounded<T>::type result_type; |
41 | result_type operator()(T x, T y) |
42 | { |
43 | if (y >= 0) // because x >= y, it follows that x >= 0, too |
44 | return result_type(x) - result_type(y); |
45 | if (x >= 0) // y < 0 |
46 | // avoid the nasty two's complement case for y == min() |
47 | return result_type(x) + result_type(-(y+1)) + 1; |
48 | // both x and y are negative: no signed overflow |
49 | return result_type(x - y); |
50 | } |
51 | }; |
52 | |
53 | /* |
54 | * Compute x + y, x is unsigned, result fits in type of "y". |
55 | */ |
56 | |
57 | template<class T1, class T2, bool sgn = (std::numeric_limits<T2>::is_signed && (std::numeric_limits<T1>::digits >= std::numeric_limits<T2>::digits))> |
58 | struct add { }; |
59 | |
60 | template<class T1, class T2> |
61 | struct add<T1, T2, /* signed or else T2 has more digits than T1 so the cast always works - needed when T2 is a multiprecision type and T1 is a native integer */ false> |
62 | { |
63 | typedef T2 result_type; |
64 | result_type operator()(T1 x, T2 y) { return T2(x) + y; } |
65 | }; |
66 | |
67 | template<class T1, class T2> |
68 | struct add<T1, T2, /* signed */ true> |
69 | { |
70 | typedef T2 result_type; |
71 | result_type operator()(T1 x, T2 y) |
72 | { |
73 | if (y >= 0) |
74 | return T2(x) + y; |
75 | // y < 0 |
76 | if (x > T1(-(y+1))) // result >= 0 after subtraction |
77 | // avoid the nasty two's complement edge case for y == min() |
78 | return T2(x - T1(-(y+1)) - 1); |
79 | // abs(x) < abs(y), thus T2 able to represent x |
80 | return T2(x) + y; |
81 | } |
82 | }; |
83 | |
84 | } // namespace detail |
85 | } // namespace random |
86 | } // namespace boost |
87 | |
88 | #endif // BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_TOOLS |
89 | |
90 | |