-/* 2^(DBL_MANT_DIG-1). */
-static const double TWO_MANT_DIG =
- /* Assume DBL_MANT_DIG <= 4 * 31.
+#ifdef USE_LONG_DOUBLE
+# define FUNC truncl
+# define DOUBLE long double
+# define MANT_DIG LDBL_MANT_DIG
+# define L_(literal) literal##L
+#elif ! defined USE_FLOAT
+# define FUNC trunc
+# define DOUBLE double
+# define MANT_DIG DBL_MANT_DIG
+# define L_(literal) literal
+#else /* defined USE_FLOAT */
+# define FUNC truncf
+# define DOUBLE float
+# define MANT_DIG FLT_MANT_DIG
+# define L_(literal) literal##f
+#endif
+
+/* 2^(MANT_DIG-1). */
+static const DOUBLE TWO_MANT_DIG =
+ /* Assume MANT_DIG <= 5 * 31.