[Haskell-cafe] How to calculate de number of digits of an integer? (was: Is logBase right?)

[Roberto López]

Ok. I wonder if someone could help me with this problem...

I want to calculate the number of digits of a positive integer. I was 
thinking of ...

	numDigits n = truncate (logBase 10 n) + 1

But (logBase 10 1000) = 2.9999999999999996 so numDigits 1000 = 2. 

Maybe adding a small amount 

	numDigits n = truncate ((logBase 10 n) + 0.0000000000000005) + 1

Prelude> numDigits 100
3
Prelude> numDigits 1000
4
Prelude> numDigits 10000
5
Prelude> numDigits 10000
5
Prelude> numDigits 100000
6
Prelude> numDigits 1000000
7
Prelude> numDigits 10000000
8
Prelude> numDigits 100000000
9
Prelude> numDigits 1000000000
9                                          <---- This is wrong!!!!
Prelude> numDigits 10000000000
11

Is there a reliable way to calculate the number of digits by means of 
logBase?


Regards!