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ILOG2(3) Library Functions Manual ILOG2(3)NAMEilog2- integer base-2 logarithmSYNOPSIS#include<sys/bitops.h>intilog2(size x);DESCRIPTIONFor positive x, theilog2() 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 isilog2(x).ERRORSilog2() returns -1 when x is zero.SEE ALSObitops(3), ffs(3), ilogb(3), log2(3), imax(9), powerof2(9)HISTORYTheilog2() macro first appeared in NetBSD 5.0. NetBSD 10.99 November 5, 2021 NetBSD 10.99