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man pages section 3: Extended Library Functions, Volume 2

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Updated: Thursday, June 13, 2019
 
 

ilogb(3M)

Name

ilogb, ilogbf, ilogbl - return an unbiased exponent

Synopsis

c99 [ flag... ] file... –lm [ library... ]
#include <math.h>

int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);
cc [ flag... ] file... –lm [ library... ]
#include <math.h>

int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);

Description

These functions return the exponent part of their argument x. Formally, the return value is the integral part of logr| x | as a signed integral value, for non-zero x, where r is the radix of the machine's floating point arithmetic, which is the value of FLT_RADIX defined in <float.h>.

Return Values

Upon successful completion, these functions return the exponent part of x as a signed integer value. They are equivalent to calling the corresponding logb(3M) function and casting the returned value to type int.

If x is 0, the value FP_ILOGB0 is returned. For SUSv3–conforming applications compiled with the c99 compiler driver (see standards(7)), a domain error occurs.

If x is ±Inf, the value INT_MAX is returned. For SUSv3–conforming applications compiled with the c99 compiler driver, a domain error occurs.

If x is NaN, the value FP_ILOGBNAN is returned. For SUSv3–conforming applications compiled with the c99 compiler driver, a domain error occurs.

Errors

These functions will fail if:

Domain Error

The x argument is zero, NaN, or ±Inf.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception is raised.

Attributes

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
Availability
system/library/math
MT-Level
MT-Safe
Standard

See Also

limits.h(3HEAD), math.h(3HEAD), feclearexcept(3M), fetestexcept(3M), logb(3M), scalb(3M), attributes(7), standards(7)