Re: GCC's -ffast-math behavior
|[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]|
于 2012/2/9 17:47, Andrew Haley 写道:
On 02/09/2012 09:35 AM, xunxun wrote:于 2012/2/9 17:21, Andrew Haley 写道:On 02/09/2012 08:33 AM, xunxun wrote:When using -ffast-math, gcc don't generate the math function symbol: U _expNo, it doesn't. Instead gcc uses the F2XM1 instruction. Why would you want to call a library when gcc has an instruction to do the job?Because other math lib works faster than gcc itself (even with fastmath), and I want to use fastmath to make other caculation faster, too.Hmm, I think that'll be difficult. We tend to assume that when a processor has built-in instructions to do something, that's the fastest way to do it. It's usually true, and I am wondering what tricks Intel uses. Granted, the floating-point transcendental instructions aren't super-fast, and perhaps Intel doesn't optimize them any more. Andrew.
Thank you for the explanation.I think I can separate all the math functions from other code, put the math functions within one lib, and don't use fastmath to build the lib. :)
-- Best Regards, xunxun