Content-type: text/html Man page of log2

# log2

Section: Mathematical Library Functions (3M)
Updated: 12 Jul 2006
Index Return to Main Contents

## NAME

log2, log2f, log2l - compute base 2 logarithm functions

## SYNOPSIS

```c99 [ flag... ] file... -lm [ library... ]
#include <math.h>
```

double log2(double x);

float log2f(float x);

long double log2l(long double x);

## DESCRIPTION

These functions compute the base 2 logarithm of their argument x, log2(x).

## RETURN VALUES

Upon successful completion, these functions return the base 2 logarithm of x.

If x is ±0, a pole error occurs and log2(), log2f(), and log2l() return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.

For finite values of x that are less than 0, or if x is -Inf a domain error occurs and a NaN is returned.

If x is NaN, a NaN is returned.

If x is 1, +0 is returned.

If x is +Inf, x is returned.

## ERRORS

These functions will fail if:

Domain Error The finite value of x is less than 0, or x is -Inf.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception is raised.

Pole Error The value of x is 0.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception is raised.

## USAGE

An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.

## ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

 ATTRIBUTE TYPE ATTRIBUTE VALUE Interface Stability Standard MT-Level MT-Safe

## SEE ALSO

feclearexcept(3M), fetestexcept(3M), log(3M), math.h(3HEAD), attributes(5), standards(5)

## Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
ERRORS
USAGE
ATTRIBUTES
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 02:39:33 GMT, October 02, 2010