libs/libm: correct implementation of truncl if long double is double

This reuses implementation of trunc in case long double has same size as
double.

The previous implementation is used only in case x87 80-bit float point
is the long double. In other cases the logic is intentionally replaced
with panic to not provide a wrong result.

Signed-off-by: Karel Kočí <kkoci@elektroline.cz>

Author: Cynerd

libs/libm/libm/lib_truncl.c

@@ -35,6 +35,7 @@
 #include <nuttx/config.h>
 #include <nuttx/compiler.h>
 
+#include <assert.h>
 #include <stdint.h>
 #include <float.h>
 #include <math.h>
@@ -44,9 +45,18 @@
  ****************************************************************************/
 
 #ifdef CONFIG_HAVE_LONG_DOUBLE
-static const long double toint = 1 / LDBL_EPSILON;
+#if LDBL_MANT_DIG == DBL_MANT_DIG
+
+/* Cover case when double is the same as long double (64 bit ieee754). */
+
+long double truncl(long double x)
+{
+  return trunc(x);
+}
 
-/* FIXME This will only work if long double is 64 bit and little endian */
+#elif LDBL_MANT_DIG == 64
+
+static const long double toint = 1 / LDBL_EPSILON;
 
 union ldshape
 {
@@ -100,4 +110,13 @@ long double truncl(long double x)
   x += y;
   return s ? -x : x;
 }
+
+#else
+
+long double truncl(long double x)
+{
+  PANIC();  /* FIX ME */
+}
+
+#endif
 #endif