Hello, I just want to point out that this looks very similar to a qemuppc machine bug we've seen before with libm and floor() call: https://bugzilla.yoctoproject.org/show_bug.cgi?id=4854
It was fixed with: http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=2a48e9007cc92fedfdb6919411859fb943eacc94 HTH, Stefan On Wed, 2014-03-12 at 15:30 +0000, Mats Kärrman wrote: > Hi, > > I face a problem with libm. With my Dora build the following assertion > doesn't hold: > > sqrt( pow( sqrt( 2.0 ), 4.0 ) ) == 2.0 > > 1) With my old OE-classic / glibc-2.9 / PowerPC-hf it holds. > 2) With my Debian desktop PC / glibc-2.17 / amd64 it holds. > 3) With my new OE-core Dora / eglibc-2.18 / PowerPC-hf it doesn't hold. > > Close enough one can think but the standardized test case I run requires the > result to be 2.0. > A simple test program: > -------------------------------------------------------------------- > #include <stdio.h> > #include <math.h> > > int main(){ > > double two = 2.0; > double four = 4.0; > > double s1 = sqrt(two); > printf("sqrt(%.20f) = %.20f\n", two, s1); > double p = pow(s1, four); > printf("pow(%.20f, %.20f) = %.20f\n", s1, four, p); > double s2 = sqrt(p); > printf("sqrt(%.20f) = %.20f\n", p, s2); > > } > -------------------------------------------------------------------- > > results from 1 and 2 (identical): > sqrt(2.00000000000000000000) = 1.41421356237309514547 > pow(1.41421356237309514547, 4.00000000000000000000) = 4.00000000000000088818 > sqrt(4.00000000000000088818) = 2.00000000000000000000 > > results from 3: > sqrt(2.00000000000000000000) = 1.41421356237309492343 > pow(1.41421356237309492343, 4.00000000000000000000) = 3.99999999999999866773 > sqrt(3.99999999999999866773) = 1.99999999999999955591 > > Does anyone know if this is a known "feature" of eglibc or know any other > reason > for this difference? > > Best Regards, > Mats -- _______________________________________________ Openembedded-core mailing list Openembedded-core@lists.openembedded.org http://lists.openembedded.org/mailman/listinfo/openembedded-core
