ILOGB(3) | Library Functions Manual | ILOGB(3)

# NAME

`ilogb`, `ilogbf`, `ilogbl` — extract exponent

# SYNOPSIS

Math Library (libm, -lm)
`#include <math.h>`

int
`ilogb`(double x);

int
`ilogbf`(float x);

int
`ilogbl`(long double x);

# DESCRIPTION

`ilogb`() returns x's exponent n, in integer format. `ilogb`(±infinity) returns `INT_MAX`, `ilogb`(NaN) returns `FP_ILOGBNAN` and `ilogb`(0) returns `FP_ILOGB0`. The `ilogbf`() function is a single precision version of `ilogb`(). The `ilogbl`() function is an extended precision version of `ilogb`().

# SEE ALSO

ffs(3), frexp(3)

# STANDARDS

IEEE Std 754-1985

# HISTORY

The `ilogb`, `ilogbf` and `ilogbl` functions appeared in 4.3BSD, NetBSD 1.1 and OpenBSD 4.5, respectively.

June 7, 2025 | Debian