log2(), log2f(), log2l()

Updated: May 06, 2022

Compute the base-2 logarithm of a number

Synopsis:

#include <math.h>

double log2( double x );

float log2f( float x );

long double log2l( long double x );

Arguments:

x
The number that you want to compute the base-2 log of.

Library:

libm
The general-purpose math library.
libm-sve
(QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

Description:

The log2(), log2f(), and log2l() functions compute the base-2 logarithm of x:

log2x

To check for error situations, use feclearexcept() and fetestexcept(). For example:

Returns:

The base-2 logarithm of x.

If x is: These functions return: Errors:
x is ±0.0 -Inf FE_DIVBYZERO
1.0 0.0
Less than 0.0 and finite, or -Inf NaN FE_INVALID
Inf Inf
NaN NaN

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

Classification:

C11, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes