On 22 January 2014 22:36, Philippe Waroquiers <philippe.waroqui...@skynet.be> wrote: > On Wed, 2014-01-22 at 00:19 +0100, Lionel Cons wrote: >> On 22 January 2014 00:03, Tom Hughes <t...@compton.nu> wrote: >> > On 21/01/14 21:49, Tina Harriott wrote: >> > >> >> I am new to this list. Can anyone guide me dissect a problem with >> >> valgrinds long double fp math on x86-64 cpus? We're getting major >> >> malfunctions in our applications because any long double operation >> >> (say y=sinl(x)) contains rubbish in the least significant bits. >> > >> > See the "Limitations" section of the manual: >> > >> > http://www.valgrind.org/docs/manual/manual-core.html#manual-core.limits >> > >> > Specifically the section about floating point limitations. >> >> "...Whether or not this is critical remains to be seen..." >> >> Yeah, that comment is so 'funny' that it hurts again. The difference >> between 64bit math and 80bit math is whether a MBDA Meteor missile >> will hit its target or not (Michael Östergren holds a personal grudge >> against valgrind because of weeks lost due this particular >> embarrassing bug screwing up simulations btw), whether the beams in >> LHC will meet the (intended!) target or not, whether math in SAS >> software works or not (warranting a warning in the written >> documentation that running with valgrind to test 3rd party plugins is >> not supported). So the list of things which do *NOT* work with >> valgrind is *impressive* and hurt high value projects, IMHO warranting >> at least the removal of that mocking comment "...Whether or not this >> is critical remains to be seen...". Please. > Effectively, it looks clear that many applications have problems > with this aspect. Would be better to rephrase the doc :). > > Now, maybe these applications should better be compilable > with 64 bits floats, and would/should then work properly natively > and under valgrind. > > The gcc documentation says for -mfpmath=sse: > > The resulting code should be considerably faster in the majority of > cases and avoid the numerical instability problems of 387 code, but > may break some existing code that expects temporaries to be 80 > bits. > > So, you might try to compile your app with the above flag > (I guess you might need a #ifdef or so to have a typedef that > is 80 bits without the above, and 64 bits with the above). > > But of course, we all agree it would be nice to have 80 bits floats > properly supported by Valgrind. It is just nobody has time/money/effort > to spend on that :(.
Kickstarter project maybe? Tina -- Tina Harriott - Women in Mathematics Contact: tina.harriott.m...@gmail.com ------------------------------------------------------------------------------ WatchGuard Dimension instantly turns raw network data into actionable security intelligence. It gives you real-time visual feedback on key security issues and trends. Skip the complicated setup - simply import a virtual appliance and go from zero to informed in seconds. http://pubads.g.doubleclick.net/gampad/clk?id=123612991&iu=/4140/ostg.clktrk _______________________________________________ Valgrind-users mailing list Valgrind-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/valgrind-users
