New module 'isnanl-nolibm'.

[gnulib.git] / lib / isnanl.c

diff --git a/lib/isnanl.c b/lib/isnanl.c
new file mode 100644 (file)
index 0000000..0412c55
--- /dev/null
+++ b/lib/isnanl.c
@@ -0,0 +1,62 @@
+/* Test for NaN that does not need libm.
+   Copyright (C) 2007 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License along
+   with this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2007.  */
+
+#include <config.h>
+
+#include <float.h>
+#include <string.h>
+
+#define LDBL_EXP_MASK ((LDBL_MAX_EXP - LDBL_MIN_EXP) | 7)
+
+#define NWORDS \
+  ((sizeof (long double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
+typedef union { long double value; unsigned int word[NWORDS]; }
+        memory_long_double;
+
+int
+rpl_isnanl (long double x)
+{
+#if defined LDBL_EXPBIT0_WORD && defined LDBL_EXPBIT0_BIT
+  /* Be careful to not do any floating-point operation on x, such as x == x,
+     because x may be a signalling NaN.  */
+  static memory_long_double nan = { 0.0L / 0.0L };
+  static long double plus_inf = 1.0L / 0.0L;
+  static long double minus_inf = -1.0L / 0.0L;
+  memory_long_double m;
+
+  /* A NaN can be recognized through its exponent.  But exclude +Infinity and
+     -Infinity, which have the same exponent.  */
+  m.value = x;
+  if ((((m.word[LDBL_EXPBIT0_WORD] >> LDBL_EXPBIT0_BIT)
+       ^ (nan.word[LDBL_EXPBIT0_WORD] >> LDBL_EXPBIT0_BIT))
+       & LDBL_EXP_MASK)
+      == 0)
+    return (memcmp (&m.value, &plus_inf, sizeof (long double)) != 0
+           && memcmp (&m.value, &minus_inf, sizeof (long double)) != 0);
+  else
+    return 0;
+#else
+  /* The configuration did not find sufficient information.  Give up about
+     the signaling NaNs, handle only the quiet NaNs.  */
+  if (x == x)
+    return 0;
+  else
+    return 1;
+#endif
+}