frexp, frexpf, frexpl
| 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) |
x into a normalized fraction and an integral power of two.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
argis ±0, it is returned, unmodified, and0is stored in *exp. - If
argis ±∞, it is returned, and an unspecified value is stored in *exp. - If
argis 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
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
#include <float.h> #include <math.h> #include <stdio.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
- C23 standard (ISO/IEC 9899:2024):
- 7.12.6.4 The frexp functions (p: TBD)
- 7.25 Type-generic math <tgmath.h> (p: TBD)
- F.10.3.4 The frexp functions (p: TBD)
- C17 standard (ISO/IEC 9899:2018):
- 7.12.6.4 The frexp functions (p: TBD)
- 7.25 Type-generic math <tgmath.h> (p: TBD)
- F.10.3.4 The frexp functions (p: TBD)
- 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
| (C99)(C99) |
multiplies a number by 2 raised to a power (function) |
| (C99)(C99)(C99) |
extracts exponent of the given number (function) |
| (C99)(C99)(C99) |
extracts exponent of the given number (function) |
| (C99)(C99) |
breaks a number into integer and fractional parts (function) |
| C++ documentation for frexp
| |