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Command: ilog2 | Section: 3 | Source: NetBSD | File: ilog2.3
ILOG2(3) FreeBSD 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.
FreeBSD 14.1-RELEASE-p8 November 5, 2021 FreeBSD 14.1-RELEASE-p8