On 1/28/07, Fernando Perez <[EMAIL PROTECTED]> wrote: > On 1/28/07, Charles R Harris <[EMAIL PROTECTED]> wrote: > > > > The problem goes away if I remove atlas (atlas3-sse2 for me). But that > > > just introduces another problem: slowness. > > > > > > So is this something to report to Clint Whaley? Or does it have to do > > > with how numpy uses atlas? > > > > > > Interesting, I wonder if ATLAS is resetting the FPU flags and changing the > > rounding mode? It is just the LSB of the mantissa that looks to be > > changing. Before reporting the problem it might be good to pin it down a bit > > more if possible. > > Well, the fact that I don't see the problem on a PentiumIII (with > atlas-sse) but I see it on my desktop (atlas-sse2) should tell us > something. The test code uses double arrays, and SSE2 has double > precision support but it's purely 64-bit doubles. SSE is > single-precision only, which means that for a double computation, > ATLAS isn't used and the Intel FPU does the computation instead. > Intel FPUs use 80 bits internally for intermediate operations (even > though they only return a normal 64-bit double result), so it's fairly > common to see this kind of thing.
Removing ATLAS SSE2 does fix the problem. But why does test1 pass when ATLAS SSE2 is present? _______________________________________________ Numpy-discussion mailing list [email protected] http://projects.scipy.org/mailman/listinfo/numpy-discussion
