X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=lib%2Ffloor.c;h=05a6591a4b40a183307ed04d9f4e04f22a4f64d1;hb=56093e4d947bcc87bbc05ac3e8645509274f57b4;hp=7b5c9c9e33dcd1b3ccf6b33c8bb12adbd4c6d9fa;hpb=57fdfd3f8ec62b105c53bcdf6f127c35c7fe7391;p=gnulib.git

diff --git a/lib/floor.c b/lib/floor.c
index 7b5c9c9e3..05a6591a4 100644
--- a/lib/floor.c
+++ b/lib/floor.c
@@ -41,7 +41,7 @@
 #endif
 
 /* 2^(MANT_DIG-1).  */
-static const double TWO_MANT_DIG =
+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).  */
@@ -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;
 }