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Hi! On Thu, 04 Apr 2013 16:26:17 +0200, Andreas Jaeger <aj@suse.com> wrote: > On Thursday, April 04, 2013 16:17:45 Thomas Schwinge wrote: > > On Thu, 04 Apr 2013 09:38:58 +0200, Andreas Jaeger <aj@suse.com> > wrote: > > > On Wednesday, April 03, 2013 22:03:31 Thomas Schwinge wrote: > > > > @@ -139,7 +141,7 @@ __ieee754_pow(double x, double y) { > > > > > > > > } > > > > else if (qx == 0x7ff00000) > > > > > > > > return y < 0 ? 0.0 : INF.x; > > > > > > > > - return NaNQ.x; /* y not > > > > integer and x<0 */ + return (x - x) / (x - x); > > > > /* y not integer and x<0 */> > > > I'm not convinced of this change, the rest is fine. > > > > > > The above raises an invalid exception - but the previous code did > > > not. Why is this change still fine? > > > > If my code and specification reading is correct, then this is a bug in > > the original code, for IEEE 754-2008 says: Âpow (x, y) signals the > > invalid operation exception for finite x < 0 and finite non-integer > > yÂ, and/but this didn't matter in practice, as the wrapper code in > > math/w_pow.c:__pow would catch this case and handle it separately via > > sysdeps/ieee754/k_standard.c:__kernel_standard, case 24, raising an > > INVALID exception on its own. Can you confirm my reasoning? > > I wonder whether your change really does, what it should. > > You want to pass the same NAN back that was passed in My primary goal with this patch is to get rid of the hard-coded qNaN bit pattern, which is wrong for MIPS and HPPA (meaning sNaN for these two). > kernel_standard always passes a new NAN out. So, shouldn't you change > k_standard.c accordingly as well? Getting the payloads of returned NaNs to contain something sensible is a logically separate change, and will require a lot of modification all over glibc's math code, and I'm not working on that at the moment. That I changed some of the dbl-64 pow code from returning a new qNaN to returning the NaN that was already present as a function input is just because it was an obvious thing to do for such cases. > > We could be adding the respective tests to libm-tests with > > <http://news.gmane.org/find-root.php?message_id=%3C871uaqzheb.fsf%40sc > > hwinge.name%3E> (or something similar) in place. > > libm-tests already checks for the invalid exception, It does, but only for the default POSIX error handing mode, which is provided (at least for the case we're discussing here) by __kernel_standard, case 24, but libm-tests does not check for the right exceptions being set in IEEE error handling mode, for example. GrÃÃe, Thomas
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