X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=lib%2Ftrunc.c;h=a10184e352a59c1a3e90825f97887f62c0a96061;hb=a3984e06bca84a7654624dd754a7c4c7a5a39a59;hp=385e2d139cdf03cc4b4cd94c50be9ea534f425e1;hpb=57fdfd3f8ec62b105c53bcdf6f127c35c7fe7391;p=gnulib.git

diff --git a/lib/trunc.c b/lib/trunc.c
index 385e2d139..a10184e35 100644
--- a/lib/trunc.c
+++ b/lib/trunc.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).  */
@@ -65,21 +65,29 @@ FUNC (DOUBLE x)
 
   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 -= L_(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 < 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 += L_(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;
 }