ilog2(3) - NetBSD Manual Pages

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ILOG2(3)                NetBSD Library Functions Manual               ILOG2(3)


NAME

     ilog2 -- integer base-2 logarithm


SYNOPSIS

     #include <sys/bitops.h>

     int
     ilog2(size x);


DESCRIPTION

     For positive x, the 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).


ERRORS

     ilog2() returns -1 when x is zero.


SEE ALSO

     bitops(3), ffs(3), ilogb(3), log2(3), imax(9), powerof2(9)


HISTORY

     The ilog2() macro first appeared in NetBSD 5.0.

NetBSD 10.0                    November 5, 2021                    NetBSD 10.0