New <math.h> macro named issignaling to check for a signaling NaN (sNaN).

It is based on draft TS 18661 and currently enabled as a GNU extension.

1 files changed, 46 insertions, 0 deletions

diff --git a/sysdeps/ieee754/dbl-64/s_issignaling.c b/sysdeps/ieee754/dbl-64/s_issignaling.c
new file mode 100644
index 0000000000..f475bc7bdf
--- /dev/null
+++ b/sysdeps/ieee754/dbl-64/s_issignaling.c
@@ -0,0 +1,46 @@
+/* Test for signaling NaN.
+   Copyright (C) 2013 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <math.h>
+#include <math_private.h>
+
+int
+__issignaling (double x)
+{
+#ifdef HIGH_ORDER_BIT_IS_SET_FOR_SNAN
+  u_int32_t hxi;
+  GET_HIGH_WORD (hxi, x);
+  /* We only have to care about the high-order bit of x's significand, because
+     having it set (sNaN) already makes the significand different from that
+     used to designate infinity.  */
+  return (hxi & 0x7ff80000) == 0x7ff80000;
+#else
+  u_int32_t hxi, lxi;
+  EXTRACT_WORDS (hxi, lxi, x);
+  /* To keep the following comparison simple, toggle the quiet/signaling bit,
+     so that it is set for sNaNs.  This is inverse to IEEE 754-2008 (as well as
+     common practice for IEEE 754-1985).  */
+  hxi ^= 0x00080000;
+  /* If lxi != 0, then set any suitable bit of the significand in hxi.  */
+  hxi |= (lxi | -lxi) >> 31;
+  /* We have to compare for greater (instead of greater or equal), because x's
+     significand being all-zero designates infinity not NaN.  */
+  return (hxi & 0x7fffffff) > 0x7ff80000;
+#endif
+}
+libm_hidden_def (__issignaling)