Hi John, >>> The likely cause is __float128 operations being performed as "double >>> precision" >>> of two __float80 by the Intel math library for x86_64. Memcheck-3.8.1 >>> implements >>> __float80 operations as __float64 (ordinary IEEE-754 'double'.) > >> Thanks for analyzing this! I assume this means that a fix will be rather >> complex? > > Nearly every user whose programs utilize 80-bit x86 floating point > is disappointed by memcheck's 64-bit implementation of 80-bit operations. > This situation is many years old. The fix requires a major effort > of design and implementation.
If you don't mind me saying so, this is a pretty incomprehensible design decision. This is virtually guaranteed to change the behavior of the code, which I would think is a big no-no for a debugging tool. But I guess we need to deal with what we have now... So I see only two options: - disable the unit tests that fail when running under valgrind. - switch to gcc's libquadmath. A casual inspection suggests that this is based on gmp. It may well be slower than Intel's implementation though... I would also need to test if it is mature enough by now. > If all of your use of 80-bit operations on x86 is indirect as the result > of __float128, then perhaps you could run on s390, where memcheck has > good support for the 128-bit hardware floating point. Unfortunately I do not have access to such a platform. I am very surprised that there even is hardware support for 128-bit FP. I always thought that that would be too much of a fringe market to be profitable. Cheers, Peter. -- Peter van Hoof Royal Observatory of Belgium Ringlaan 3 1180 Brussel Belgium http://homepage.oma.be/pvh ------------------------------------------------------------------------------ October Webinars: Code for Performance Free Intel webinars can help you accelerate application performance. Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from the latest Intel processors and coprocessors. See abstracts and register > http://pubads.g.doubleclick.net/gampad/clk?id=60133471&iu=/4140/ostg.clktrk _______________________________________________ Valgrind-users mailing list Valgrind-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/valgrind-users
