Tribblix: manual page: log2.3m

LOG2(3M) Mathematical Library Functions LOG2(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