[PATCH] Update sparc ULPs.

[David Miller]

From: "Joseph S. Myers" <joseph@codesourcery.com>
Date: Mon, 24 Sep 2012 19:48:44 +0000

> If x is small enough (absolute value less than LDBL_EPSILON / 2.0L, I 
> think) then the correct rounded-to-nearest result of log1pl (x) is just x, 
> so code can test for that case and avoid the more complicated calculations 
> with potential underflow (while taking care to generate underflow if 
> correct).  Properly, that's x with inexact exception (if not 0), and 
> underflow exception if x is subnormal (or, on tinyness-before-rounding 
> machines, if x is +LDBL_MIN, but that detail isn't something I'd expect 
> glibc to implement).

Indeed, that seems to do the trick.  I used an int conversion to
force the exception as that seems to be the cheapest way to do
this in the soft-fp library.

What I really don't understand is why ldbl-128ibm's variant of this
code doesn't trigger this same problem on powerpc testsuite runs.
Either it is happening (and therefore ldbl-128ibm/s_log1pl.c needs a
similar change to this) or powerpc isn't generating the exceptions.

Anyways, any objections to this patch?

2012-11-15  David S. Miller  <davem@davemloft.net>

	* sysdeps/ieee754/ldbl-128/s_log1pl.c (__log1pl): If xm1 is
	smaller than LDBL_EPSILON/2.0L, just return xm1.

diff --git a/sysdeps/ieee754/ldbl-128/s_log1pl.c b/sysdeps/ieee754/ldbl-128/s_log1pl.c
index 4ecea0f..fad18e9 100644
--- a/sysdeps/ieee754/ldbl-128/s_log1pl.c
+++ b/sysdeps/ieee754/ldbl-128/s_log1pl.c
@@ -138,6 +138,12 @@ __log1pl (long double xm1)
       && (u.parts32.w1 | u.parts32.w2 | u.parts32.w3) == 0)
     return xm1;
 
+  if ((hx & 0x7fffffff) < 0x3f8e0000)
+    {
+      if ((int) xm1 == 0)
+	return xm1;
+    }
+
   x = xm1 + 1.0L;
 
   /* log1p(-1) = -inf */