ilogb(), ilogbf(), ilogbl()
QNX SDP8.0C Library ReferenceAPIDeveloper
Compute the integral part of a logarithm
Synopsis:
#include <math.h>
int ilogb( double x );
int ilogbf( float x );
int ilogbl( long double x );
Arguments:
- x
- The number for which you want to compute the integral part of the logarithm.
Library:
- libm
- The general-purpose math library.
- libm-sve
- A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.
Your system requirements will determine how you should work with these libraries:
- If you want only selected processes to run with the SVE version, you can include both libraries in your OS image and use the -l m or -l m-sve option to qcc to link explicitly against the appropriate one.
- If you want all processes to use the SVE version, include libm-sve.so in your OS image and set up a symbolic link from libm.so to libm-sve.so. Use the -l m option to qcc to link against the library.
Note:
Compile your program with the -fno-builtin option to prevent the compiler from using a
built-in version of the function.
Description:
The ilogb(), ilogbf(), and ilogbl() functions compute the integral part of:
logr |x|
as a signed integral value, for nonzero finite x, where r is the radix of the machine's floating point arithmetic.
To check for error situations, use feclearexcept() and fetestexcept(). For example:
- Call
feclearexcept(FE_ALL_EXCEPT)before calling ilogb(), ilogbf(), or ilogbl(). - On return, if
fetestexcept(FE_ALL_EXCEPT)is nonzero, then an error has occurred.
Returns:
The exponent part of x, in integer format.
| If x is: | These functions return: | Errors: |
|---|---|---|
| 0.0 | FP_ILOGB0 | — |
| NaN | FP_ILOGBNAN | — |
| ±Inf | INT_MAX | — |
These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.
Classification:
| Safety: | |
|---|---|
| Cancellation point | No |
| Signal handler | Yes |
| Thread | Yes |
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