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[Bug target/34702] [4.3 Regression] 1.0 is not the inverse of 1.0 with -mrecip on x86
- From: "dominiq at lps dot ens dot fr" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 8 Jan 2008 10:17:02 -0000
- Subject: [Bug target/34702] [4.3 Regression] 1.0 is not the inverse of 1.0 with -mrecip on x86
- References: <bug-34702-12313@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #3 from dominiq at lps dot ens dot fr 2008-01-08 10:17 -------
I just had a look to the doc patch in
http://gcc.gnu.org/ml/gcc-patches/2008-01/msg00273.html:
...
+Note that while the throughput of the sequence is higher than the throughput
+of the non-reciprocal instruction, the precision of the sequence can be
+decreased up to 2 ulp.
It looks nice, but could you add (after converting my frenglish) something
along the line "in particular the inverse of 1.0 is no longer 1.0, but
0.99999994" (or nearest(1.0,-1.0) or its C* equivalent).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34702