Fix for issue #871 (#872)

Author: mborland

include/boost/math/ccmath/abs.hpp

@@ -12,6 +12,7 @@
 #include <type_traits>
 #include <limits>
 #include <boost/math/tools/is_constant_evaluated.hpp>
+#include <boost/math/tools/assert.hpp>
 #include <boost/math/ccmath/isnan.hpp>
 #include <boost/math/ccmath/isinf.hpp>
 
@@ -28,19 +29,29 @@ namespace boost::math::ccmath {
 namespace detail {
 
 template <typename T> 
-inline constexpr T abs_impl(T x) noexcept
+constexpr T abs_impl(T x) noexcept
 {
-    return boost::math::ccmath::isnan(x) ? std::numeric_limits<T>::quiet_NaN() : 
-           boost::math::ccmath::isinf(x) ? std::numeric_limits<T>::infinity() : 
-           x == -0 ? T(0) :
-           x == (std::numeric_limits<T>::min)() ? std::numeric_limits<T>::quiet_NaN() : 
-           x > 0 ? x : -x;
+    if (boost::math::ccmath::isnan(x))
+    {
+        return std::numeric_limits<T>::quiet_NaN();
+    }
+    else if (x == static_cast<T>(-0))
+    {
+        return static_cast<T>(0);
+    }
+
+    if constexpr (std::is_integral_v<T>)
+    {
+        BOOST_MATH_ASSERT(x != (std::numeric_limits<T>::min)());
+    }
+    
+    return x >= 0 ? x : -x;
 }
 
 } // Namespace detail
 
 template <typename T, std::enable_if_t<!std::is_unsigned_v<T>, bool> = true>
-inline constexpr T abs(T x) noexcept
+constexpr T abs(T x) noexcept
 {
     if(BOOST_MATH_IS_CONSTANT_EVALUATED(x))
     {
@@ -56,7 +67,7 @@ inline constexpr T abs(T x) noexcept
 // If abs() is called with an argument of type X for which is_unsigned_v<X> is true and if X
 // cannot be converted to int by integral promotion (7.3.7), the program is ill-formed.
 template <typename T, std::enable_if_t<std::is_unsigned_v<T>, bool> = true>
-inline constexpr T abs(T x) noexcept
+constexpr T abs(T x) noexcept
 {
     if constexpr (std::is_convertible_v<T, int>)
     {
@@ -69,12 +80,12 @@ inline constexpr T abs(T x) noexcept
     }
 }
 
-inline constexpr long int labs(long int j) noexcept
+constexpr long int labs(long int j) noexcept
 {
     return boost::math::ccmath::abs(j);
 }
 
-inline constexpr long long int llabs(long long int j) noexcept
+constexpr long long int llabs(long long int j) noexcept
 {
     return boost::math::ccmath::abs(j);
 }