This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
frexp, frexpf, frexpl — extract mantissa and exponent from a double precision number
double frexp(double num, int *exp);
float frexpf(float num, int *exp);
long double frexpl(long double num, int *exp);
The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1‐2008 defers to the ISO C standard.
These functions shall break a floating-point number num into a normalized fraction and an integral power of 2. The integer exponent shall be stored in the int object pointed to by exp.
For finite arguments, these functions shall return the value x, such that x has a magnitude in the interval [½,1) or 0, and num equals x times 2 raised to the power * exp.
If num is NaN, a NaN shall be returned, and the value of * exp is unspecified.
If num is ±0, ±0 shall be returned, and the value of * exp shall be 0.
If num is ±Inf, num shall be returned, and the value of * exp is unspecified.
No errors are defined.
The following sections are informative.
isnan(), ldexp(), modf()
The Base Definitions volume of POSIX.1‐2008, <math.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .
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