NAME

logb — return exponent as a floating-point number

SYNOPSIS

#include <math.h>

double
logb(double x);

long double
logbl(long double x);

float
logbf(float x);

DESCRIPTION

The logb() functions return the exponent of x, represented as a floating-point number.

SPECIAL VALUES

logb(±0) returns -infinity and raises the "divide-by-zero" floating-point exception.

logb(±infinity) returns +infinity.

VECTOR OPERATIONS

If you need to apply the logb() functions to SIMD vectors or arrays, using the following functions provided by the Accelerate.framework may give significantly better performance:

#include <Accelerate/Accelerate.h>

vFloat vlogbf(vFloat x);
void vvlogbf(float *y, const float *x, const int *n);
void vvlogb(double *y, const double *x, const int *n);

SEE ALSO

ilogb(3) log(3) math(3)

STANDARDS

The logb() functions conform to ISO/IEC 9899:2011.