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log2.3m (2010 09)

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log2(3M) log2(3M)
NAME
log2( ), log2f( ), log2l( ), log2w( ), log2q( ) - logarithm base two functions
SYNOPSIS
#include <math.h>
double log2(double x);
float log2f(float x);
HP Integrity Server Only
long double log2l(long double x);
extended log2w(extended x);
quad log2q(quad x);
DESCRIPTION
log2() returns the logarithm base two of x.
log2f() is a float version of log2(); it takes a
float argument and returns a float result.
Integrity Server Only
log2l() is a long double version of log2(); it takes a long double argument and returns a
long double result.
log2w() is an extended version of log2(); it takes an extended argument and returns an
extended result.
log2q() is equivalent to log2l() on HP-UX systems.
USAGE
To use these functions, compile either with the default
-Ae option or with the -Aa
and
-D_HPUX_SOURCE options.
To use (for Integrity servers)
log2w() or log2q(), compile also with the -fpwidetypes option.
Make sure your program includes
<math.h>, and link in the math library by specifying -lm
on the com-
piler or linker command line.
For more information, see the HP-UX floating-point guide for HP Integrity servers at the following site:
http://www.hp.com/go/fp
.
RETURN VALUE
If x is +INFINITY,
log2() returns +INFINITY.
If x is zero,
log2() returns − HUGE_VAL (equal to −INFINITY) and raises the divide-by-zero exception.
If x is less than zero,
log2() returns NaN and raises the invalid exception.
If x is NaN,
log2() returns NaN.
log2() raises the inexact exception whenever a rounded result does not equal the mathematical result.
ERRORS
If x is less than zero,
log2() sets errno to [EDOM].
Integrity Server Only
HP-UX
libm functions on Integrity servers do not set errno by default. For errno setting, compile
with the +Olibmerrno option.
SEE ALSO
exp(3M), exp10(3M), log(3M), log1p(3M), log2(3M), pow(3M), math(5).
STANDARDS CONFORMANCE
log2(), log2f(), log2l() : ISO/IEC C99 (including Annex F, ‘‘IEC 60559 floating-point arithmetic’’)
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

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