frexp(3) — Subroutines

NAME

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

SYNOPSIS

#include <math.h>
double frexp(
        double x,
        int ∗n ); float frexpf(
        float x,
        int ∗n ); long double frexpl(
        long double x,
        int ∗n ); double ldexp(
        double y,
        int n ); float ldexpf(
        float y,
        int n ); long double ldexpl(
        long double y,
        int n ); double logb(
        double x ); float logbf(
        float x ); long double logbl(
        long double x ); double scalb(
        double x,
        double n ); float scalbf(
        float x,
        float n ); long double scalbl(
        long double x,
        long double n );

LIBRARY

Math Library (libm)

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

The logb(), logbf(), and logbl() 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(), scalbf(), and scalbl() functions are defined as x∗(2∗∗n) for integer n.

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

Function	Exceptional Argument	Routine Behavior
frexp(), frexpf(), frexpl()	\|x\| = infinity	Invalid argument
logb(), logbf(), logbl()	\|x\| = infinity	Invalid argument
scalb(), scalbf(), scalbl()	x∗(2∗∗n) > max_float	Overflow
scalb(), scalbf(), scalbl()	x∗(2∗∗n) < min_float	Underflow
ldexp(), ldexpf(), ldexpl()	x∗(2∗∗n) > max_float	Overflow
ldexp(), ldexpf(), ldexpl()	x∗(2∗∗n) < min_float	Underflow

The following table lists boundary values used by these functions: