| ILOG2(3) | Library Functions Manual | ILOG2(3) | 
ilog2 —
#include <sys/bitops.h>
int
  
  ilog2(size
    x);
ilog2() macro
  returns the integer part of the base-2 logarithm of x;
  that is,
  floor(log_2(x));.
  If n =
  ilog2(x), then
  n is the largest integer such that
  2**n
  <= x; in other words,
  ilog2() returns the largest integer to which 2 can be
  raised to obtain a value at most x.
The type of the input parameter must be unsigned.
If x is a constant expression, then so is
    ilog2(x).
ilog2() returns -1 when x is zero.
ilog2() macro first appeared in
  NetBSD 5.0.
| November 5, 2021 | NetBSD 10.0 |