What kind of logarithm functions / methods are available in objective-c / cocoa-touch?

Question

I've tried searching for logarithm + objective-c, but all I get is math test pages from teachers, or explanations what a logarithm is ;)

I've got some measurements that are like 83912.41234 and others are 32.94232. I need to press down this huge spectrum into something between 0 and 100, and that 32.94232 would habe to be at least something bigger than 2, where the 83912.41234 would be something near 100. So I think a logarithm function will be my friend here.

UPDATE: I've came across the math.h file through "Open Quickly" (very nice command in Xcode: SHIFT + CMD + D), and there, big surprise:

extern double log ( double );
extern float logf ( float );

extern double log10 ( double );
extern float log10f ( float );

extern double log2 ( double );
extern float log2f ( float );

extern double log1p ( double );
extern float log1pf ( float );

extern double logb ( double );
extern float logbf ( float );

But: No text, no comments. I'm not such a math-freak. So some description would be good, i.e. what kind of logarithm for what case, how the curve looks like, etc... so any great links are highly appreciated!

Answer 1

Also, getting a logarithm with an arbitrary base:

float logx(float value, float base) 
{
   return log10f(value) / log10f(base);
}