Fix bug in constexpr round implementations causing values in the range 0.5-1.0 to round to zero

Author: PowellNGL

include/boost/math/ccmath/round.hpp

@@ -31,11 +31,11 @@ inline constexpr T round_impl(T arg) noexcept
     const T x = boost::math::ccmath::modf(arg, &iptr);
     constexpr T half = T(1)/2;
 
-    if(x >= half && iptr > 0)
+    if(x >= half && iptr >= 0)
     {
         return iptr + 1;
     }
-    else if(boost::math::ccmath::abs(x) >= half && iptr < 0)
+    else if(boost::math::ccmath::abs(x) >= half && iptr <= 0)
     {
         return iptr - 1;
     }

test/ccmath_round_test.cpp

@@ -40,23 +40,41 @@ constexpr void test()
     static_assert(boost::math::ccmath::lround(std::numeric_limits<T>::infinity()) == 0l);
     static_assert(boost::math::ccmath::llround(std::numeric_limits<T>::infinity()) == 0ll);
 
+    static_assert(boost::math::ccmath::round(T(0.1)) == T(0));
+    static_assert(boost::math::ccmath::round(T(0.5)) == T(1));
+    static_assert(boost::math::ccmath::round(T(0.9)) == T(1));
     static_assert(boost::math::ccmath::round(T(2.3)) == T(2));
     static_assert(boost::math::ccmath::round(T(2.5)) == T(3));
     static_assert(boost::math::ccmath::round(T(2.7)) == T(3));
+    static_assert(boost::math::ccmath::round(T(-0.1)) == T(0));
+    static_assert(boost::math::ccmath::round(T(-0.5)) == T(-1));
+    static_assert(boost::math::ccmath::round(T(-0.9)) == T(-1));
     static_assert(boost::math::ccmath::round(T(-2.3)) == T(-2));
     static_assert(boost::math::ccmath::round(T(-2.5)) == T(-3));
     static_assert(boost::math::ccmath::round(T(-2.7)) == T(-3));
 
+    static_assert(boost::math::ccmath::lround(T(0.1)) == 0l);
+    static_assert(boost::math::ccmath::lround(T(0.5)) == 1l);
+    static_assert(boost::math::ccmath::lround(T(0.9)) == 1l);
     static_assert(boost::math::ccmath::lround(T(2.3)) == 2l);
     static_assert(boost::math::ccmath::lround(T(2.5)) == 3l);
     static_assert(boost::math::ccmath::lround(T(2.7)) == 3l);
+    static_assert(boost::math::ccmath::lround(T(-0.1)) == 0l);
+    static_assert(boost::math::ccmath::lround(T(-0.5)) == -1l);
+    static_assert(boost::math::ccmath::lround(T(-0.9)) == -1l);
     static_assert(boost::math::ccmath::lround(T(-2.3)) == -2l);
     static_assert(boost::math::ccmath::lround(T(-2.5)) == -3l);
     static_assert(boost::math::ccmath::lround(T(-2.7)) == -3l);
 
+    static_assert(boost::math::ccmath::llround(T(0.1)) == 0ll);
+    static_assert(boost::math::ccmath::llround(T(0.5)) == 1ll);
+    static_assert(boost::math::ccmath::llround(T(0.9)) == 1ll);
     static_assert(boost::math::ccmath::llround(T(2.3)) == 2ll);
     static_assert(boost::math::ccmath::llround(T(2.5)) == 3ll);
     static_assert(boost::math::ccmath::llround(T(2.7)) == 3ll);
+    static_assert(boost::math::ccmath::llround(T(-0.1)) == 0ll);
+    static_assert(boost::math::ccmath::llround(T(-0.5)) == -1ll);
+    static_assert(boost::math::ccmath::llround(T(-0.9)) == -1ll);
     static_assert(boost::math::ccmath::llround(T(-2.3)) == -2ll);
     static_assert(boost::math::ccmath::llround(T(-2.5)) == -3ll);
     static_assert(boost::math::ccmath::llround(T(-2.7)) == -3ll);