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 TYPEATTRIBUTE VALUE
Interface StabilityStandard
MT-LevelMT-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

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Time: 02:39:33 GMT, October 02, 2010