Oops, fix last commit so that it also works with modf().

[gnulib.git] / lib / trunc.c

diff --git a/lib/trunc.c b/lib/trunc.c
index b74021e..31e1e77 100644 (file)
--- a/lib/trunc.c
+++ b/lib/trunc.c
@@ -1,19 +1,18 @@
 /* Round towards zero.
-   Copyright (C) 2007 Free Software Foundation, Inc.
+   Copyright (C) 2007, 2009, 2010 Free Software Foundation, Inc.
 
-   This program is free software; you can redistribute it and/or modify
+   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.
+   the Free Software Foundation; either version 3 of the License, 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.  */
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 /* Written by Bruno Haible <bruno@clisp.org>, 2007.  */
 
@@ -24,18 +23,36 @@
 
 #include <float.h>
 
-/* 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.
      Use the identity
-       n = floor(n/4) + floor((n+1)/4) + floor((n+2)/4) + floor((n+3)/4).  */
-  (double) (1U << ((DBL_MANT_DIG - 1) / 4))
-  * (double) (1U << ((DBL_MANT_DIG - 1 + 1) / 4))
-  * (double) (1U << ((DBL_MANT_DIG - 1 + 2) / 4))
-  * (double) (1U << ((DBL_MANT_DIG - 1 + 3) / 4));
+       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));
 
-double
-trunc (double x)
+DOUBLE
+FUNC (DOUBLE x)
 {
   /* The use of 'volatile' guarantees that excess precision bits are dropped
      at each addition step and before the following comparison at the caller's
@@ -43,26 +60,34 @@ trunc (double x)
      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 y = x;
-  volatile double z = y;
+  volatile DOUBLE y = x;
+  volatile DOUBLE z = y;
 
-  if (z > 0)
+  if (z > L_(0.0))
     {
-      /* Round to the next integer (nearest or up or down, doesn't matter).  */
-      z += TWO_MANT_DIG;
-      z -= TWO_MANT_DIG;
-      /* Enforce rounding down.  */
-      if (z > y)
-       z -= 1.0;
+      /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1.  */
+      if (z < TWO_MANT_DIG)
+        {
+          /* Round to the next integer (nearest or up or down, doesn't matter).  */
+          z += TWO_MANT_DIG;
+          z -= TWO_MANT_DIG;
+          /* Enforce rounding down.  */
+          if (z > y)
+            z -= L_(1.0);
+        }
     }
-  else if (z < 0)
+  else if (z < L_(0.0))
     {
-      /* Round to the next integer (nearest or up or down, doesn't matter).  */
-      z -= TWO_MANT_DIG;
-      z += TWO_MANT_DIG;
-      /* Enforce rounding up.  */
-      if (z < y)
-       z += 1.0;
+      /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1.  */
+      if (z > - TWO_MANT_DIG)
+        {
+          /* Round to the next integer (nearest or up or down, doesn't matter).  */
+          z -= TWO_MANT_DIG;
+          z += TWO_MANT_DIG;
+          /* Enforce rounding up.  */
+          if (z < y)
+            z += L_(1.0);
+        }
     }
   return z;
 }