frexp

Break floating-point number into normalized fraction and power of 2

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Contents

Interface
Description
Special Values
See Also
Standards
Page Comments

Interface

#include <math.h>double  frexp (double value, int *exp)
long  frexpl (long double value, int *exp)
float  frexpf (float value, int *exp)

Description

The frexp functions break the floating-point number value into a normalized fraction and an integral power of 2. They store the integer in the int object pointed to by exp.

The functions return a number x such that x has a magnitude in the interval $\inline [1/2, 1)$ or 0, and value = $\inline 2^\mathrm{exp} x$ .

Example:

Example - Break floating-point number into normalized fraction and power of 2

Workings

#include <stdio.h>
#include <math.h>
int main(void)
{
  double x = 1024, fraction;
  int e;
  fraction = frexp(x, &e);
  printf("x = %.2lf = %.2lf * 2^%d\n", x, fraction, e);
  return 0;
}

Solution

Output:

x = 1024.00 = 0.50 * 2^11

Special Values

frexp (0, exp) returns 0, and stores 0 in the object pointed to by exp.

frexp (∞, exp) returns ∞ and stores an unspecified value in the object pointed to by exp.

frexp (NaN, exp) returns a NaN, and stores an unspecified value in the object pointed to by exp.

Standards

The frexp functions conform to ISO/IEC 9899:1999(E).

double	`frexp` (double value, int *exp)
long	`frexpl` (long double value, int *exp)
float	`frexpf` (float value, int *exp)