NAME

frexp, ldexp, logb, scalb − Manipulate floating-point numbers

LIBRARY

Math Library (libm.a)

SYNOPSIS

#include <math.h>

double frexp  (double x, int ∗n);
float  frexpf (float  x, int ∗n);
double ldexp  (double y, int n);
float  ldexpf (float  y, int n);
double logb   (double x);
float  logbf  (float  x);
double scalb  (double x, double n);
float  scalbf (float  x, float  n);

STANDARDS

Interfaces documented on this reference page conform to industry standards as follows:

frexp():  XPG4

ldexp():  XPG4

logb():  XPG4−UNIX

scalb():  XPG4−UNIX

Refer to the standards(5) reference page for more information about industry standards and associated tags. 

DESCRIPTION

Every nonzero number can be written uniquely as the normalized mantissa (fraction) z times 2 raised to the power p, where the absolute value of z is in the range [0.5, 1.0), and the exponent p, is an integer. 

The frexp() and frexpf() functions break a floating-point number into a normalized fraction and an integral power of 2. The functions store the integer in the int object pointed to by the n parameter and return the fraction part. 

The ldexp() and ldexpf() functions multiply a floating-point number, y, by an integral power of 2. 

The logb() and logbf() functions return a signed integer converted to double-precision floating-point and so chosen that 1 <= |x|/2∗∗n < 2 unless x = 0 or |x| = infinity or x lies between 0 and the Underflow Threshold. 

IEEE 754 defines logb(+infinity) = +infinity and logb(0) = −infinity.  The latter is required to signal Division-by-Zero. 

The scalb() and scalbf() functions are defined as x∗(2∗∗n) for integer n. 

The following table describes function behavior in response to exceptional arguments:

The following table lists boundary values used by these functions: