HP-UX Reference (11i v2 03/08) - 3 Library Functions A-M (vol 6)

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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);

Itanium(R)-based System 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.

Itanium-based System 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 Itanium-based systems)

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.

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].

Itanium-based System Only

HP-UX

libm functions on Itanium-based systems do not set errno by default. For errno setting, com-

pile with the +Olibmerrno option.