formula for logarithms to base two of a number

[dynamo]

Is there a formula for finding logarithms to base two of a number.If so wtat is it.Thanks for any replying.

[Dormilich]

you mean if you don't have a calculator at hand that computes the logarithms?

there are some series you can use.

[JosAH]

There's a simple integer approximation:

int log2(unsigned int n) {
  int log = 0;
  if (n >= 1<<16) { n >>= 16; log += 16; }
  if (n >= 1<< 8) { n >>=  8; log +=  8; }
  if (n >= 1<< 4) { n >>=  4; log +=  4; }
  if (n >= 1<< 2) { n >>=  2; log +=  2; }
  if (n >= 1<< 1) {           log +=  1; }
  return ((n == 0) ? -1 : log);
}
 

(this assumes C or C++ being used).

kind regards,

Jos

[dynamo]

thanks for replying.really appreciate it