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ilog2(3) [netbsd man page]

ILOG2(3)						   BSD Library Functions Manual 						  ILOG2(3)

NAME
ilog2 -- integer logarithm SYNOPSIS
#include <sys/bitops.h> size ilog2(size x); DESCRIPTION
The ilog2() macro returns an integer (binary) logarithm of x. It is the logarithm for base 2; the binary logarithm of x is the power to which the number 2 must be raised to obtain the value x. The type of the input parameter should be either uint32_t or uint64_t. ERRORS
A value -1 is returned on error. SEE ALSO
bitops(3), ilogb(3), log2(3), imax(9), powerof2(9) HISTORY
The ilog2() macro first appeared in NetBSD 5.0. BSD
May 10, 2011 BSD

Check Out this Related Man Page

ROUNDUP(9)						   BSD Kernel Developer's Manual						ROUNDUP(9)

NAME
roundup -- macros for counting and rounding SYNOPSIS
#include <sys/param.h> size howmany(x, size); size roundup(x, size); size rounddown(x, size); size roundup2(x, size); int powerof2(x); DESCRIPTION
The roundup() and rounddown() macros return an integer from rounding x up and down, respectively, to the next size. The howmany() macro in turn reveals how many times size fits into x, rounding the residual up. The roundup2() macro also rounds up, but with the assumption that size is a power of two. If x is indeed a power of two, powerof2() return 1. RETURN VALUES
The return value is an integer from the respective operation. If x is 0, all macros except powerof2() return 0. The behavior is undefined if size is 0. EXAMPLES
The following example rounds the variable rx to a 32-bit boundary: uint16_t rx; ... rx = roundup2(rx, sizeof(uint32_t)); SEE ALSO
ilog2(3), param(3), imax(9) CAVEATS
All described macros make no assumptions about the type of the parameters. These are implicitly assumed to be unsigned integers. BSD
June 1, 2011 BSD
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