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
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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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