Gamma function: implementation?

[Brian Woodroffe]

I am trying to implement a port of a program that calls for a
"gamma" function.  Unfortunately the compiler / math's library
I am using does not have such a function.  Can any one post,
or mail me a copy of a PD - C program to implement a gamma
function?

As second question; what is a gamma function anyway? (I understand
that a factorial is the degenerate integer case.)  And what is a
gamma function used for and where?

Thank you,
Brian Woodroffe.

PS:  I am interrested in an implementation that is accurate enough
for 24-bit significand and a 7 bit exponent; base 2; ie single precision.

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