[patches] Patch for expf wrongly returning infinity (FSF glibc bug 3406)

["Joseph S. Myers" <joseph@xxxxxxxxxxxxxxxx>]

expf wrongly returns infinity when it should return a value just below
FLT_MAX, as reported in bug 3406, because w_expf.c has a wrong figure
for the largest expf input with finite float output.  The figure in
e_expf.c for the smallest expf input with infinite float output is
correct; this patch changes w_expf.c to use the correct value (the
next float lower than the one in e_expf.c).

Committed to EGLIBC trunk, 2.7, 2.6, 2.5.

Index: sysdeps/ieee754/flt-32/w_expf.c
===================================================================
--- sysdeps/ieee754/flt-32/w_expf.c	(revision 5131)
+++ sysdeps/ieee754/flt-32/w_expf.c	(working copy)
@@ -29,7 +29,7 @@
 #else
 static float
 #endif
-o_threshold=  8.8721679688e+01,  /* 0x42b17180 */
+o_threshold=  8.8722831726e+01,  /* 0x42b17217 */
 u_threshold= -1.0397208405e+02;  /* 0xc2cff1b5 */
 
 #ifdef __STDC__
Index: math/libm-test.inc
===================================================================
--- math/libm-test.inc	(revision 5131)
+++ math/libm-test.inc	(working copy)
@@ -2510,6 +2510,7 @@
   TEST_f_f (exp, 3, M_E3l);
   TEST_f_f (exp, 0.75L, 2.11700001661267466854536981983709561L);
   TEST_f_f (exp, 50.0L, 5184705528587072464087.45332293348538L);
+  TEST_f_f (exp, 88.72269439697265625L, 3.40233126623160774937554134772290447915e38L);
 #ifdef TEST_LDOUBLE
   /* The result can only be represented in long double.  */
   TEST_f_f (exp, 1000.0L, 0.197007111401704699388887935224332313e435L);
Index: ChangeLog.eglibc
===================================================================
--- ChangeLog.eglibc	(revision 5131)
+++ ChangeLog.eglibc	(working copy)
@@ -1,3 +1,9 @@
+2008-02-11  Joseph Myers  <joseph@xxxxxxxxxxxxxxxx>
+
+	[BZ #3406]
+	* sysdeps/ieee754/flt-32/w_expf.c (o_threshold): Correct value.
+	* math/libm-test.inc (exp_test): Test 88.72269439697265625.
+
 2008-02-07  Joseph Myers  <joseph@xxxxxxxxxxxxxxxx>
 
 	* Makerules (install-extras, install-map): New variables.

-- 
Joseph S. Myers
joseph@xxxxxxxxxxxxxxxx