Fix ldbl-128 expm1l (-min_subnorm) result sign (bug 18619).

In the ldbl-128 implementation of expm1l, when expm1l's result should
underflow to 0 (argument minus the least subnormal, in some rounding
modes), it can be a zero of the wrong sign.  This patch fixes this in
the same way previously used for the x86 / x86_64 versions.

Tested for mips64.

	[BZ #18619]
	* sysdeps/ieee754/ldbl-128/s_expm1l.c (__expm1l): Force underflow
	and return argument in case of subnormal argument.

diff --git a/ChangeLog b/ChangeLog
index a2fd213..7d501d5 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2015-07-01  Joseph Myers  <joseph@codesourcery.com>
+
+       [BZ #18619]
+       * sysdeps/ieee754/ldbl-128/s_expm1l.c (__expm1l): Force underflow
+       and return argument in case of subnormal argument.
+
 2015-07-01  Martin Sebor  <msebor@redhat.com>
 
        [BZ #18435]

diff --git a/NEWS b/NEWS
index 91320dd..eecc9a1 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -25,7 +25,7 @@ Version 2.22
   18496, 18497, 18498, 18502, 18507, 18512, 18513, 18519, 18520, 18522,
   18527, 18528, 18529, 18530, 18532, 18533, 18534, 18536, 18539, 18540,
   18542, 18544, 18545, 18546, 18547, 18549, 18553, 18558, 18569, 18583,
-  18585, 18586, 18593, 18594, 18602, 18612, 18613.
+  18585, 18586, 18593, 18594, 18602, 18612, 18613, 18619.
 
 * Cache information can be queried via sysconf() function on s390 e.g. with
   _SC_LEVEL1_ICACHE_SIZE as argument.

diff --git a/sysdeps/ieee754/ldbl-128/s_expm1l.c b/sysdeps/ieee754/ldbl-128/s_expm1l.c
index f708af5..573d00b 100644 (file)
--- a/sysdeps/ieee754/ldbl-128/s_expm1l.c
+++ b/sysdeps/ieee754/ldbl-128/s_expm1l.c
@@ -137,9 +137,18 @@ __expm1l (long double x)
   if (x < minarg)
     return (4.0/big - 1.0L);
 
-  /* Avoid internal underflow when result does not underflow.  */
-  if (fabsl (x) < 0x1p-113L && fabsl (x) >= LDBL_MIN)
-    return x;
+  /* Avoid internal underflow when result does not underflow, while
+     ensuring underflow (without returning a zero of the wrong sign)
+     when the result does underflow.  */
+  if (fabsl (x) < 0x1p-113L)
+    {
+      if (fabsl (x) < LDBL_MIN)
+       {
+         long double force_underflow = x * x;
+         math_force_eval (force_underflow);
+       }
+      return x;
+    }
 
   /* Express x = ln 2 (k + remainder), remainder not exceeding 1/2. */
   xx = C1 + C2;                        /* ln 2. */