frexp, frexpf, frexpl

 

C

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headers

Type support

Dynamic memory management

Error handling

Program utilities

Variadic function support

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

Technical Specifications

 

Numerics

Common mathematical functions

Floating-point environment

Complex number arithmetics

Random number generation

Type-generic math

 

Common mathematical functions

Functions
Basic operations
abslabsllabsimaxabs (C99) fabs divldivlldivimaxdiv (C99) fmod	remainder (C99) remquo (C99) fma (C99) fmax (C99) fmin (C99) fdim (C99) nannanfnanl (C99)(C99)(C99)
Exponential functions
exp exp2 (C99) expm1 (C99)	log log10 log1p (C99) log2 (C99)
Power functions
sqrt cbrt (C99)	hypot (C99) pow
Trigonometric and hyperbolic functions
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C99) acosh (C99) atanh (C99)
Error and gamma functions
erf (C99) erfc (C99)	lgamma (C99) tgamma (C99)
Nearest integer floating point operations
ceil floor roundlroundllround (C99)(C99)(C99)	trunc (C99) nearbyint (C99) rintlrintllrint (C99)(C99)(C99)
Floating point manipulation functions
ldexp scalbnscalbln (C99)(C99) ilogb (C99) logb (C99)	frexp modf nextafternexttoward (C99)(C99) copysign (C99)
Classification
fpclassify (C99) isfinite (C99) isinf (C99) isnan (C99) isnormal (C99) signbit (C99)	isgreater (C99) isgreaterequal (C99) isless (C99) islessequal (C99) islessgreater (C99) isunordered (C99)
Macro constants
HUGE_VALFHUGE_VALHUGE_VALL (C99)(C99)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C99)(C99)(C99)(C99)(C99)

 

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.

Parameters

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

Return value

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

Otherwise (if arg is not zero), if no errors occur, returns the value x in the range (-1;-0.5], [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.

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

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.

Example

Run this code

#include <stdio.h>
#include <math.h>
#include <float.h>
 
int main(void)
{
    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

References

• C11 standard (ISO/IEC 9899:2011):

• 7.12.6.4 The frexp functions (p: 243)

• 7.25 Type-generic math <tgmath.h> (p: 373-375)

• F.10.3.4 The frexp functions (p: 521)

• C99 standard (ISO/IEC 9899:1999):

• 7.12.6.4 The frexp functions (p: 224)

• 7.22 Type-generic math <tgmath.h> (p: 335-337)

• F.9.3.4 The frexp functions (p: 458)

• C89/C90 standard (ISO/IEC 9899:1990):

• 4.5.4.2 The frexp function

See also

ldexpldexpfldexpl (C99)(C99)	multiplies a number by 2 raised to a power (function)
logblogbflogbl (C99)(C99)(C99)	extracts exponent of the given number (function)
ilogbilogbfilogbl (C99)(C99)(C99)	extracts exponent of the given number (function)
modfmodffmodfl (C99)(C99)	breaks a number into integer and fractional parts (function)
C++ documentation for frexp