autoupdate

[gnulib.git] / lib / floor.c

diff --git a/lib/floor.c b/lib/floor.c
index 7ee7486..593b526 100644 (file)
--- a/lib/floor.c
+++ b/lib/floor.c
@@ -1,5 +1,5 @@
 /* Round towards negative infinity.
-   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
    it under the terms of the GNU General Public License as published by
@@ -63,20 +63,31 @@ FUNC (DOUBLE x)
   volatile DOUBLE y = x;
   volatile DOUBLE z = y;
 
-  /* Round to the next integer (nearest or up or down, doesn't matter).  */
   if (z > L_(0.0))
     {
-      z += TWO_MANT_DIG;
-      z -= TWO_MANT_DIG;
+      /* 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 < L_(0.0))
     {
-      z -= TWO_MANT_DIG;
-      z += TWO_MANT_DIG;
+      /* 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);
+        }
     }
-  /* Enforce rounding down.  */
-  if (z > y)
-    z -= L_(1.0);
-
   return z;
 }