1// (C) Copyright Matt Borland 2021.
2// Use, modification and distribution are subject to the
3// Boost Software License, Version 1.0. (See accompanying file
4// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
5//
6// Constepxr implementation of abs (see c.math.abs secion 26.8.2 of the ISO standard)
7
8#ifndef BOOST_MATH_CCMATH_ABS
9#define BOOST_MATH_CCMATH_ABS
10
11#include <boost/math/ccmath/detail/config.hpp>
12
13#ifdef BOOST_MATH_NO_CCMATH
14#error "The header <boost/math/abs.hpp> can only be used in C++17 and later."
15#endif
16
17#include <boost/math/tools/assert.hpp>
18#include <boost/math/ccmath/isnan.hpp>
19#include <boost/math/ccmath/isinf.hpp>
20
21namespace boost::math::ccmath {
22
23namespace detail {
24
25template <typename T>
26constexpr T abs_impl(T x) noexcept
27{
28 if ((boost::math::ccmath::isnan)(x))
29 {
30 return std::numeric_limits<T>::quiet_NaN();
31 }
32 else if (x == static_cast<T>(-0))
33 {
34 return static_cast<T>(0);
35 }
36
37 if constexpr (std::is_integral_v<T>)
38 {
39 BOOST_MATH_ASSERT(x != (std::numeric_limits<T>::min)());
40 }
41
42 return x >= 0 ? x : -x;
43}
44
45} // Namespace detail
46
47template <typename T, std::enable_if_t<!std::is_unsigned_v<T>, bool> = true>
48constexpr T abs(T x) noexcept
49{
50 if(BOOST_MATH_IS_CONSTANT_EVALUATED(x))
51 {
52 return detail::abs_impl<T>(x);
53 }
54 else
55 {
56 using std::abs;
57 return abs(x);
58 }
59}
60
61// If abs() is called with an argument of type X for which is_unsigned_v<X> is true and if X
62// cannot be converted to int by integral promotion (7.3.7), the program is ill-formed.
63template <typename T, std::enable_if_t<std::is_unsigned_v<T>, bool> = true>
64constexpr T abs(T x) noexcept
65{
66 if constexpr (std::is_convertible_v<T, int>)
67 {
68 return detail::abs_impl<int>(x: static_cast<int>(x));
69 }
70 else
71 {
72 static_assert(sizeof(T) == 0, "Taking the absolute value of an unsigned value not convertible to int is UB.");
73 return T(0); // Unreachable, but suppresses warnings
74 }
75}
76
77constexpr long int labs(long int j) noexcept
78{
79 return boost::math::ccmath::abs(x: j);
80}
81
82constexpr long long int llabs(long long int j) noexcept
83{
84 return boost::math::ccmath::abs(x: j);
85}
86
87} // Namespaces
88
89#endif // BOOST_MATH_CCMATH_ABS
90

source code of boost/libs/math/include/boost/math/ccmath/abs.hpp