On 11/15/2011 08:51 AM, James Hirschorn wrote:
I guess "fold" means do the computation at compile time?
No, it is being called with a variable. That is interesting that libc has a
gamma function. I will have to track down the implementation ...
-----Original Message-----
From: Ian Lance Taylor [mailto:i...@google.com]
Sent: Tuesday, November 15, 2011 1:58 AM
To: James Hirschorn
Cc: gcc@gcc.gnu.org; james.hirsch...@gmail.com
Subject: Re: builtin gamma function
James Hirschorn<james.hirsch...@hotmail.com> writes:
I have noticed that the builtin gamma function is very accurate and
extremely fast. Can someone tell me where to find the source code for the
implementation?
Are you calling it on a constant? Because gcc will fold gamma applied
to a constant which meets certain characteristics.
If you aren't calling it on a constant, then you are getting the
function from your libc. gcc does not itself include an implementation
of the gamma function.
Ian
The Lancsos algorithm should be pretty fast. OTOH there are a few logs
and some divisions.
I'm betting they have a polynomial fit from 0 to 1 and then do
\Gamma(x+1) = x\Gamma(x) or something.
Also, Maybe we could use constexpr in C++11 mode in some cases.
