6.11.86 ilogbl Function

Calculates the signed integer exponent of a long double precision floating-point value.

Include

<math.h>

Prototype

int ilogbl(long double x);

Argument

x

any positive value for which to return the exponent

Return Value

Returns the exponent of x as a signed integer value. If x is 0, it returns the value FP_ILOGB0; if x is infinite, it returns the value INT_MAX; if x is a NaN it returns the value FP_ILOGBNAN; otherwise, this will yield the same value as the corresponding logb function cast to type int.

Example

See the notes at the beginning of this chapter or section for information on using printf() or scanf() (and other functions reading and writing the stdin or stdout streams) in the example code.

#include <math.h>
#include <stdio.h>
#include <errno.h>

int main(void)
{
  double x;
  int y;

  errno = 0;
  x = 13.45;
  y = ilogbl(x);
  if (errno)
    perror("Error");
  printf("The exponent of %f is %d\n", x, y);

  errno = 0;
  x = 0.0;
  y = ilogbl(x);
  if (errno)
    perror("Error");
  printf("The exponent of %f is %d\n", x, y);

  errno = 0;
  x = -2.0;
  y = ilogbl(x);
  if (errno)
    perror("Error");
  printf("The exponent of %f is %d\n", x, y);
}

Example Output

The exponent of 13.450000 is 3
The exponent of 0.000000 is -2147483648
The exponent of -2.000000 is 1