Constexpr logb and ilogb

doc/sf/ccmath.qbk

@@ -70,6 +70,15 @@ All of the following functions require C++17 or greater.
         template <typename Integer>
         inline constexpr div_t<Integer> div(Integer x, Integer y);
 
+        template <typename Real>
+        inline constexpr Real logb(Real arg);
+
+        template <typename Integer>
+        inline constexpr double logb(Integer arg);
+
+        template <typename T>
+        inline constexpr int ilogb(T arg);
+
     } // Namespaces
 
 [endsect] [/section:ccmath Constexpr CMath]

include/boost/math/ccmath/ccmath.hpp

@@ -17,5 +17,7 @@
 #include <boost/math/ccmath/fpclassify.hpp>
 #include <boost/math/ccmath/frexp.hpp>
 #include <boost/math/ccmath/div.hpp>
+#include <boost/math/ccmath/logb.hpp>
+#include <boost/math/ccmath/ilogb.hpp>
 
 #endif // BOOST_MATH_CCMATH_HPP

include/boost/math/ccmath/ilogb.hpp

@@ -0,0 +1,57 @@
+//  (C) Copyright Matt Borland 2021.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_MATH_CCMATH_ILOGB_HPP
+#define BOOST_MATH_CCMATH_ILOGB_HPP
+
+#include <cmath>
+#include <type_traits>
+#include <boost/math/tools/is_constant_evaluated.hpp>
+#include <boost/math/ccmath/logb.hpp>
+#include <boost/math/ccmath/isinf.hpp>
+#include <boost/math/ccmath/isnan.hpp>
+#include <boost/math/ccmath/abs.hpp>
+
+namespace boost::math::ccmath {
+
+// If arg is not zero, infinite, or NaN, the value returned is exactly equivalent to static_cast<int>(std::logb(arg))
+template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
+inline constexpr int ilogb(Real arg) noexcept
+{
+    if(BOOST_MATH_IS_CONSTANT_EVALUATED(arg))
+    {
+        return boost::math::ccmath::abs(arg) == Real(0) ? FP_ILOGB0 :
+               boost::math::ccmath::isinf(arg) ? INT_MAX :
+               boost::math::ccmath::isnan(arg) ? FP_ILOGBNAN :
+               static_cast<int>(boost::math::ccmath::logb(arg));
+    }
+    else
+    {
+        using std::ilogb;
+        return ilogb(arg);
+    }
+}
+
+template <typename Z, std::enable_if_t<std::is_integral_v<Z>, bool> = true>
+inline constexpr int ilogb(Z arg) noexcept
+{
+    return boost::math::ccmath::ilogb(static_cast<double>(arg));
+}
+
+inline constexpr int ilogbf(float arg) noexcept
+{
+    return boost::math::ccmath::ilogb(arg);
+}
+
+#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+inline constexpr int ilogbl(long double arg) noexcept
+{
+    return boost::math::ccmath::ilogb(arg);
+}
+#endif
+
+} // Namespaces
+
+#endif // BOOST_MATH_CCMATH_ILOGB_HPP

include/boost/math/ccmath/logb.hpp

@@ -0,0 +1,74 @@
+//  (C) Copyright Matt Borland 2021.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_MATH_CCMATH_LOGB_HPP
+#define BOOST_MATH_CCMATH_LOGB_HPP
+
+#include <cmath>
+#include <limits>
+#include <type_traits>
+#include <boost/math/tools/is_constant_evaluated.hpp>
+#include <boost/math/ccmath/frexp.hpp>
+#include <boost/math/ccmath/isinf.hpp>
+#include <boost/math/ccmath/isnan.hpp>
+#include <boost/math/ccmath/abs.hpp>
+
+namespace boost::math::ccmath {
+
+namespace detail {
+
+// The value of the exponent returned by std::logb is always 1 less than the exponent returned by 
+// std::frexp because of the different normalization requirements: for the exponent e returned by std::logb, 
+// |arg*r^-e| is between 1 and r (typically between 1 and 2), but for the exponent e returned by std::frexp, 
+// |arg*2^-e| is between 0.5 and 1. 
+template <typename T>
+inline constexpr T logb_impl(T arg) noexcept
+{
+    int exp = 0;
+    boost::math::ccmath::frexp(arg, &exp);
+
+    return exp - 1;
+}
+
+} // Namespace detail
+
+template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
+inline constexpr Real logb(Real arg) noexcept
+{
+    if(BOOST_MATH_IS_CONSTANT_EVALUATED(arg))
+    {
+        return boost::math::ccmath::abs(arg) == Real(0) ? -std::numeric_limits<Real>::infinity() :
+               boost::math::ccmath::isinf(arg) ? std::numeric_limits<Real>::infinity() :
+               boost::math::ccmath::isnan(arg) ? std::numeric_limits<Real>::quiet_NaN() :
+               boost::math::ccmath::detail::logb_impl(arg);
+    }
+    else
+    {
+        using std::logb;
+        return logb(arg);
+    }
+}
+
+template <typename Z, std::enable_if_t<std::is_integral_v<Z>, bool> = true>
+inline constexpr double logb(Z arg) noexcept
+{
+    return boost::math::ccmath::logb(static_cast<double>(arg));
+}
+
+inline constexpr float logbf(float arg) noexcept
+{
+    return boost::math::ccmath::logb(arg);
+}
+
+#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+inline constexpr long double logbl(long double arg) noexcept
+{
+    return boost::math::ccmath::logb(arg);
+}
+#endif
+
+} // Namespaces
+
+#endif // BOOST_MATH_CCMATH_LOGB_HPP

test/Jamfile.v2

@@ -131,6 +131,8 @@ test-suite special_fun :
    [ run ccmath_frexp_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
    [ run ccmath_ldexp_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
    [ run ccmath_div_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
+   [ run ccmath_logb_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
+   [ run ccmath_ilogb_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
    [ run log1p_expm1_test.cpp test_instances//test_instances pch_light ../../test/build//boost_unit_test_framework  ]
    [ run powm1_sqrtp1m1_test.cpp test_instances//test_instances pch_light ../../test/build//boost_unit_test_framework  ]
    [ run special_functions_test.cpp ../../test/build//boost_unit_test_framework  ]

test/ccmath_ilogb_test.cpp

@@ -0,0 +1,56 @@
+//  (C) Copyright Matt Borland 2021.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <cmath>
+#include <cfloat>
+#include <cstdint>
+#include <limits>
+#include <type_traits>
+#include <boost/math/ccmath/ilogb.hpp>
+#include <boost/math/ccmath/isnan.hpp>
+#include <boost/math/ccmath/isinf.hpp>
+
+#ifdef BOOST_HAS_FLOAT128
+#include <boost/multiprecision/float128.hpp>
+#endif
+
+template <typename T>
+constexpr void test()
+{
+    if constexpr (std::numeric_limits<T>::has_quiet_NaN)
+    {
+        static_assert(boost::math::ccmath::ilogb(std::numeric_limits<T>::quiet_NaN()) == FP_ILOGBNAN, "If arg is a NaN, FP_ILOGBNAN is returned.");
+    }
+
+    static_assert(boost::math::ccmath::ilogb(T(0)) == FP_ILOGB0, "If arg is zero, FP_ILOGB0 is returned");
+    static_assert(boost::math::ccmath::ilogb(std::numeric_limits<T>::infinity()) == INT_MAX, "If arg is infinite, INT_MAX is returned");
+
+    // 123.45 = 1.92891 * 2^6
+    constexpr int test_exp = boost::math::ccmath::ilogb(T(123.45));
+    static_assert(test_exp == 6);
+}
+
+#if !defined(BOOST_MATH_NO_CONSTEXPR_DETECTION) && !defined(BOOST_MATH_USING_BUILTIN_CONSTANT_P)
+int main()
+{
+    test<float>();
+    test<double>();
+
+    #ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+    test<long double>();
+    #endif
+    
+    #ifdef BOOST_HAS_FLOAT128
+    test<boost::multiprecision::float128>();
+    #endif
+
+    return 0;
+}
+#else
+int main()
+{
+    return 0;
+}
+#endif

test/ccmath_logb_test.cpp

@@ -0,0 +1,60 @@
+//  (C) Copyright Matt Borland 2021.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <cmath>
+#include <cfloat>
+#include <cstdint>
+#include <limits>
+#include <type_traits>
+#include <boost/math/ccmath/logb.hpp>
+#include <boost/math/ccmath/isnan.hpp>
+#include <boost/math/ccmath/isinf.hpp>
+
+#ifdef BOOST_HAS_FLOAT128
+#include <boost/multiprecision/float128.hpp>
+#endif
+
+template <typename T>
+constexpr void test()
+{
+    if constexpr (std::numeric_limits<T>::has_quiet_NaN)
+    {
+        static_assert(boost::math::ccmath::isnan(boost::math::ccmath::logb(std::numeric_limits<T>::quiet_NaN())), "if arg is NaN, NaN is returned");
+    }
+
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::logb(T(0))), "If arg is +-0, -infinity is returned");
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::logb(T(-0))), "If arg is +-0, -infinity is returned");
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::logb(std::numeric_limits<T>::infinity())),
+                  "if arg is +-infinity, infinity is returned");
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::logb(-std::numeric_limits<T>::infinity())),
+                  "if arg is +-infinity, infinity is returned");
+
+    // 123.45 = 1.92891 * 2^6
+    constexpr T test_exp = boost::math::ccmath::logb(T(123.45));
+    static_assert(test_exp == T(6));
+}
+
+#if !defined(BOOST_MATH_NO_CONSTEXPR_DETECTION) && !defined(BOOST_MATH_USING_BUILTIN_CONSTANT_P)
+int main()
+{
+    test<float>();
+    test<double>();
+
+    #ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+    test<long double>();
+    #endif
+    
+    #ifdef BOOST_HAS_FLOAT128
+    test<boost::multiprecision::float128>();
+    #endif
+
+    return 0;
+}
+#else
+int main()
+{
+    return 0;
+}
+#endif

test/compile_test/ccmath_ilogb_incl_test.cpp

@@ -0,0 +1,16 @@
+//  (C) Copyright Matt Borland 2021.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/math/ccmath/ilogb.hpp>
+#include "test_compile_result.hpp"
+
+void compile_and_link_test()
+{
+   check_result<int>(boost::math::ccmath::ilogb(1.0f));
+   check_result<int>(boost::math::ccmath::ilogb(1.0));
+#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+   check_result<int>(boost::math::ccmath::ilogb(1.0l));
+#endif
+}

test/compile_test/ccmath_logb_incl_test.cpp

@@ -0,0 +1,16 @@
+//  (C) Copyright Matt Borland 2021.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/math/ccmath/logb.hpp>
+#include "test_compile_result.hpp"
+
+void compile_and_link_test()
+{
+   check_result<float>(boost::math::ccmath::logb(1.0f));
+   check_result<double>(boost::math::ccmath::logb(1.0));
+#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+   check_result<long double>(boost::math::ccmath::logb(1.0l));
+#endif
+}