The ilogb() function returns the exponent part of x. Formally, the return value is the integral part of log_r|x| as a signed integral value, for non-zero finite x, where r is the radix of the machine's floating point arithmetic.

Upon successful completion, ilogb() returns the exponent part of x.

If x is 0, ilogb() returns -INT_MAX.

If x is NaN or +-Inf, ilogb() returns INT_MAX.

See attributes(5) for descriptions of the following attributes:

logb(3M), attributes(5)