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frexp, frexpf, frexpl

From cppreference.com
< c‎ | numeric‎ | math
 
 
 
Common mathematical functions
Functions
Basic operations
(C99)
(C99)
(C99)
(C99)
(C99)
(C99)(C99)(C99)
Exponential functions
(C99)
(C99)
(C99)
(C99)
Power functions
(C99)
(C99)
Trigonometric and hyperbolic functions
(C99)
(C99)
(C99)
Error and gamma functions
(C99)
(C99)
(C99)
(C99)
Nearest integer floating point operations
(C99)(C99)(C99)
(C99)
(C99)(C99)(C99)
Floating point manipulation functions
(C99)(C99)
(C99)
(C99)
frexp
Classification
(C99)
(C99)
(C99)
Macro constants
 
Defined in header <math.h>
float       frexpf( float arg, int* exp );
(1) (since C99)
double      frexp( double arg, int* exp );
(2)
long double frexpl( long double arg, int* exp );
(3) (since C99)
Defined in header <tgmath.h>
#define frexp( arg, exp )
(4) (since C99)
1-3) Decomposes given floating point value x into a normalized fraction and an integral power of two
4) Type-generic macro: If arg has type long double, frexpl is called. Otherwise, if arg has integer type or the type double, frexp is called. Otherwise, frexpf is called, respectively.

Contents

[edit] Parameters

arg - floating point value
exp - pointer to integer value to store the exponent to

[edit] Return value

If arg is zero, returns zero and stores zero in *exp.

Otherwise, if no errors occur, returns the value x in the range [0.5; 1) and stores an integer value in *exp such that x×2(*exp)
=arg

If the value to be stored in *exp is outside the range of int, the behavior is unspecified.

If arg is not a floating-point number, the behavior is unspecified.

[edit] Error handling

This function is not subject to any errors specified in math_errhandling

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

  • If arg is ±0, it is returned, unmodified, and 0 is stored in *exp.
  • If arg is ±∞, it is returned, and an unspecified value is stored in *exp.
  • If arg is NaN, NaN is returned, and an unspecified value is stored in *exp.
  • No floating-point exceptions are raised.
  • If FLT_RADIX is 2 (or a power of 2), the returned value is exact, the current rounding mode is ignored

[edit] Notes

On a binary system (where FLT_RADIX is 2), frexp may be implemented as

{
    *exp = (value == 0) ? 0 : (int)(1 + logb(value));
    return scalbn(value, -(*exp));
}

The function frexp, together with its dual, ldexp, can be used to manipulate the representation of a floating-point number without direct bit manipulations.

[edit] Example

#include <stdio.h>
#include <math.h>
#include <float.h>
 
int main()
{
    double f = 123.45;
    printf("Given the number %.2f or %a in hex,\n", f, f);
 
    double f3;
    double f2 = modf(f, &f3);
    printf("modf() makes %.0f + %.2f\n", f3, f2);
 
    int i;
    f2 = frexp(f, &i);
    printf("frexp() makes %f * 2^%d\n", f2, i);
 
    i = ilogb(f);
    printf("logb()/ilogb() make %f * %d^%d\n", f/scalbn(1.0, i), FLT_RADIX, i);
}

Possible output:

Given the number 123.45 or 0x1.edccccccccccdp+6 in hex,
modf() makes 123 + 0.45
frexp() makes 0.964453 * 2^7
logb()/ilogb() make 1.92891 * 2^6

[edit] See also

multiplies a number by 2 raised to a power
(function) [edit]
(C99)(C99)(C99)
extracts exponent of the given number
(function) [edit]
(C99)(C99)(C99)
extracts exponent of the given number
(function) [edit]
(C99)(C99)
breaks a number into integer and fractional parts
(function) [edit]