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Compute the integral part of a logarithm
#include <math.h>
int ilogb ( double x );
int ilogbf (float x );
- x
- The number you want to compute the integral part of the logarithm.
libm
Use the -l m option to
qcc
to link against this library.
The ilogb() and ilogbf() 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.
The exponent part of x, in integer format:
If x is: |
ilogb() returns: |
0 |
-INT_MAX |
NAN |
INT_MAX |
negative infinity |
INT_MAX |
positive infinity |
INT_MAX |
|
If an error occurs, these functions return 0, but this is also a valid
mathematical result.
If you want to check for errors, set
errno
to 0, call the function, and then check errno again.
These functions don't change errno if no errors occurred. |
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main( void )
{
printf( "%f\n", ilogb(.5) );
return EXIT_SUCCESS;
}
ANSI,
POSIX 1003.1
Safety: | |
Cancellation point |
No |
Interrupt handler |
No |
Signal handler |
No |
Thread |
Yes |
log(),
logb(),
log10(),
log1p()
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