Hi, I do not complain about the sin/cos performance but only on the float variants.
Using -ffast-math gives a nice performance boost but leads to bad results (in our cases which may be different from the simple given example) so it's not really a workaround. In fact, I don't really care about super-accuracy and the glibc standard implementations gives us good results. Maybe sinf/cosf in 32 bits is a bit broken but that worked for us in terms of precision and performance. On 64 bits, I can only rely on precision, as performance is gone :( Jerome On Wednesday 17 March 2010, Vincent Lefevre wrote: > On 2010-03-06 11:42:51 +0100, Jerome Vizcaino wrote: > > After many tests and research I've come to the conclusion that the > > float variants of > > sin/cos (and maybe others) are anormaly slow Debian amd64. > > Note that on amd64, sin and cos may be slow, but at least they are > mostly correct (in rounding to nearest only). In 32-bit mode (-m32), > the hardware fsin/fcos instructions (and implementation) are used, > but they are buggy on large arguments, just like sincos in 64-bit > mode (which uses the hardware instruction fsincos), and not as > accurate as the MathLib version on small arguments (even though > MathLib has a bug in its error analysis for sin). > > If you don't mind about correctness, you can still use the -ffast-math > GCC option (you don't use it in your Makefile). Depending on the > application, this can be OK, but don't complain if you get incorrect, > inaccurate or unexpected results in some cases. > > This was for sin/cos. I don't know how sinf/cosf are implemented > in 32-bit and 64-bit modes, but make sure they don't have the same > problem. If they do, this bug is invalid. > > Regards, > -- To UNSUBSCRIBE, email to debian-glibc-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/201003171931.16812.vizcaino_jer...@yahoo.fr
