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authorJoseph Myers <joseph@codesourcery.com>2015-06-23 14:35:18 +0000
committerJoseph Myers <joseph@codesourcery.com>2015-06-23 14:35:18 +0000
commitb59549574efeeecf124de05c9183c120eaaa56f0 (patch)
treeae18151390fc556d7ad3fa74246b032ce9dd6db8 /NEWS
parentb57525f1a376149840f740a31535681c07152ba4 (diff)
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Fix exp2, exp2f spurious underflows (bug 18219).
The dbl-64 and flt-32 implementations of exp2 functions produce
spurious underflow exceptions.  The underlying reason is the same in
both cases: the computation works as (2^a - 1)*2^b + 2^b for suitably
chosen a and b, where a has small magnitude so 2^a - 1 can be computed
with a low-degree polynomial approximation, and (2^a - 1)*2^b can
underflow even when the final result does not.  This patch fixes this
by adjusting the threshold for when scaling is used to avoid
intermediate underflow so it works for any possible value of a where
the final result would not underflow.

Tested for x86_64 and x86.

	[BZ #18219]
	* sysdeps/ieee754/dbl-64/e_exp2.c (__ieee754_exp2): Reduce
	threshold on absolute value of exponent for which scaling is used.
	* sysdeps/ieee754/flt-32/e_exp2f.c (__ieee754_exp2f): Likewise.
	* math/auto-libm-test-in: Add more tests of exp2.
	* math/auto-libm-test-out: Regenerated.
Diffstat (limited to 'NEWS')
-rw-r--r--NEWS12
1 files changed, 6 insertions, 6 deletions
diff --git a/NEWS b/NEWS
index d1032510fb..42ebdd1af6 100644
--- a/NEWS
+++ b/NEWS
@@ -18,12 +18,12 @@ Version 2.22
   17991, 17996, 17998, 17999, 18007, 18019, 18020, 18029, 18030, 18032,
   18034, 18036, 18038, 18039, 18042, 18043, 18046, 18047, 18049, 18068,
   18080, 18093, 18100, 18104, 18110, 18111, 18116, 18125, 18128, 18138,
-  18185, 18196, 18197, 18206, 18210, 18211, 18217, 18220, 18221, 18234,
-  18244, 18247, 18287, 18319, 18324, 18333, 18346, 18397, 18409, 18410,
-  18412, 18418, 18422, 18434, 18444, 18468, 18469, 18470, 18479, 18483,
-  18495, 18496, 18497, 18498, 18507, 18512, 18513, 18519, 18520, 18522,
-  18527, 18528, 18529, 18530, 18532, 18533, 18534, 18536, 18539, 18540,
-  18542, 18544, 18545, 18546, 18547, 18553, 18558, 18569.
+  18185, 18196, 18197, 18206, 18210, 18211, 18217, 18219, 18220, 18221,
+  18234, 18244, 18247, 18287, 18319, 18324, 18333, 18346, 18397, 18409,
+  18410, 18412, 18418, 18422, 18434, 18444, 18468, 18469, 18470, 18479,
+  18483, 18495, 18496, 18497, 18498, 18507, 18512, 18513, 18519, 18520,
+  18522, 18527, 18528, 18529, 18530, 18532, 18533, 18534, 18536, 18539,
+  18540, 18542, 18544, 18545, 18546, 18547, 18553, 18558, 18569.
 
 * Cache information can be queried via sysconf() function on s390 e.g. with
   _SC_LEVEL1_ICACHE_SIZE as argument.