rint: Support for MSVC.

[gnulib.git] / lib / rint.c

diff --git a/lib/rint.c b/lib/rint.c
new file mode 100644 (file)
index 0000000..4ba3fe5
--- /dev/null
+++ b/lib/rint.c
@@ -0,0 +1,110 @@
+/* Round according to the current rounding mode.
+   Copyright (C) 2007, 2010-2011 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.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <math.h>
+
+#include <float.h>
+#include <stdlib.h>
+
+#undef MIN
+
+#ifdef USE_LONG_DOUBLE
+# define RINT rintl
+# define DOUBLE long double
+# define MANT_DIG LDBL_MANT_DIG
+# define MIN LDBL_MIN
+# define L_(literal) literal##L
+#elif ! defined USE_FLOAT
+# define RINT rint
+# define DOUBLE double
+# define MANT_DIG DBL_MANT_DIG
+# define MIN DBL_MIN
+# define L_(literal) literal
+#else /* defined USE_FLOAT */
+# define RINT rintf
+# define DOUBLE float
+# define MANT_DIG FLT_MANT_DIG
+# define MIN FLT_MIN
+# define L_(literal) literal##f
+#endif
+
+/* -0.0.  See minus-zero.h.  */
+#if defined __hpux || defined __sgi || defined __ICC
+# define MINUS_ZERO (-MIN * MIN)
+#else
+# define MINUS_ZERO L_(-0.0)
+#endif
+
+DOUBLE
+RINT (DOUBLE x)
+{
+  /* 2^(MANT_DIG-1).  */
+  static const DOUBLE TWO_MANT_DIG =
+    /* Assume MANT_DIG <= 5 * 31.
+       Use the identity
+       n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5).  */
+    (DOUBLE) (1U << ((MANT_DIG - 1) / 5))
+    * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5))
+    * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5))
+    * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5))
+    * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5));
+
+  /* The use of 'volatile' guarantees that excess precision bits are dropped at
+     each addition step and before the following comparison at the caller's
+     site.  It is necessary on x86 systems where double-floats are not IEEE
+     compliant by default, to avoid that the results become platform and
+     compiler option dependent.  'volatile' is a portable alternative to gcc's
+     -ffloat-store option.  */
+  volatile DOUBLE z = x;
+
+  /* Consider the current rounding mode, cf.
+     <http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/float.h.html>.
+     This implementation supports only rounds-to-nearest.  */
+  if (FLT_ROUNDS != 1)
+    abort ();
+
+  if (z > L_(0.0))
+    {
+      /* Avoid rounding error for x = 0.5 - 2^(-MANT_DIG-1).  */
+      if (z < L_(0.5))
+        z = L_(0.0);
+      /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1.  */
+      else if (z < TWO_MANT_DIG)
+        {
+          /* Round to the next integer.  */
+          z += TWO_MANT_DIG;
+          z -= TWO_MANT_DIG;
+        }
+    }
+  else if (z < L_(0.0))
+    {
+      /* Avoid rounding error for x = -(0.5 - 2^(-MANT_DIG-1)).  */
+      if (z > - L_(0.5))
+        z = MINUS_ZERO;
+      /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1.  */
+      else if (z > -TWO_MANT_DIG)
+        {
+          /* Round to the next integer.  */
+          z -= TWO_MANT_DIG;
+          z += TWO_MANT_DIG;
+        }
+    }
+  return z;
+}