math: allow to create real numbers from long doubles

src/lol/math/real.h

@@ -45,6 +45,7 @@ public:
 
     Real(float f);
     Real(double f);
+    Real(long double f);
     Real(int32_t i);
     Real(uint32_t i);
     Real(int64_t i);
@@ -54,6 +55,7 @@ public:
 
     operator float() const;
     operator double() const;
+    operator long double() const;
     operator int() const;
     operator unsigned int() const;
 
@@ -171,6 +173,7 @@ public:
     __LOL_REAL_OP_HELPER_INT(unsigned int)
     __LOL_REAL_OP_HELPER_FLOAT(float)
     __LOL_REAL_OP_HELPER_FLOAT(double)
+    __LOL_REAL_OP_HELPER_FLOAT(long double)
 
     /* Constants */
     static Real<N> const& R_0();
@@ -217,6 +220,7 @@ template<> real const &real::operator =(real const &x);
 template<> real::~Real();
 template<> real::Real(float f);
 template<> real::Real(double f);
+template<> real::Real(long double f);
 template<> real::Real(int32_t i);
 template<> real::Real(uint32_t i);
 template<> real::Real(int64_t i);
@@ -225,6 +229,7 @@ template<> real::Real(char const *str);
 
 template<> real::operator float() const;
 template<> real::operator double() const;
+template<> real::operator long double() const;
 template<> real::operator int() const;
 template<> real::operator unsigned int() const;
 template<> real real::operator +() const;

src/math/real.cpp

@@ -136,6 +136,16 @@ template<> real::Real(double d)
     memset(m_mantissa + 2, 0, (BIGITS - 2) * sizeof(m_mantissa[0]));
 }
 
+template<> real::Real(long double f)
+{
+    /* We don’t know the long double layout, so we split it into
+     * two doubles instead. */
+    double hi = double(f);
+    double lo = double(f - (long double)hi);;
+    new(this) real(hi);
+    *this += lo;
+}
+
 template<> real::operator float() const { return (float)(double)(*this); }
 template<> real::operator int() const { return (int)(double)(*this); }
 template<> real::operator unsigned() const { return (unsigned)(double)(*this); }
@@ -175,6 +185,13 @@ template<> real::operator double() const
     return u.d;
 }
 
+template<> real::operator long double() const
+{
+    double hi = double(*this);
+    double lo = double(*this - hi);
+    return (long double)(hi) + (long double)(lo);
+}
+
 /*
  * Create a real number from an ASCII representation
  */

src/t/math/real.cpp

@@ -102,6 +102,22 @@ lolunit_declare_fixture(real_test)
         lolunit_assert_doubles_equal(a6, 1234567876543210.0, 0.0);
     }
 
+    lolunit_declare_test(long_double_to_real)
+    {
+        real r((long double)1 / 3);
+
+        // Count how many bits are correct
+        int ok_bits = 0;
+        while (int(r) == 0)
+        {
+            r = (r * 4) - 1;
+            ok_bits += 2;
+        }
+
+        // 64 bits means our precision is better than double
+        lolunit_assert_greater(ok_bits, 64);
+    }
+
     lolunit_declare_test(init)
     {
         real r;