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man pages section 3: Extended Library Functions, Volume 2

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Updated: Thursday, June 13, 2019
 
 

log2l(3M)

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(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
Availability
system/library/math
MT-Level
MT-Safe
Standard

See Also

math.h(3HEAD), feclearexcept(3M), fetestexcept(3M), log(3M), attributes(7), standards(7)