We do not disclose algorithmic details of math library functions implemented in our products.
Widely known approximations of gamma functions are Stirling's and Lanczos's ones. Good overview of the function along with its approximations can be found here http://mathworld.wolfram.com/GammaFunction.html. You might also want to look at numerical analysis classic book by Abramowitz and Stegun "Handbook of Mathematical Functions".
Widely known approximations of gamma functions are Stirling's and Lanczos's ones
Thank you Sergey for your answer.
I have already implemented gamma function with the help of stirling approximation.Code and run-time tests can be found here http://software.intel.com/en-us/forums/showthread.php?t=106032 I had a problem with an accuracy in the range [0.001,1.0] and was curious how it was solved by Intel programmers(my problem was solved with the help of minimax approximation in problematic range).
I have a Stegun and Avramovitz classic book which serves me well as source ofvariousformulas for my mathematical library.
I do understand that such a discussion will not be possible here.