logb

Defined in header <math.h>
float       logbf( float arg );		(since C99)
double      logb( double arg );		(since C99)
long double logbl( long double arg );		(since C99)

Extracts the value of the exponent from the floating-point argument arg, and returns it as a floating-point value. Formally, the result is the integral part of log
r|arg| as a signed floating-point value, for non-zero arg, where r is FLT_RADIX. If arg is subnormal, it is treated as though it was normalized.

Parameters

arg

-

floating point value

Return value

The floating-point exponent.

Domain or range error may occur if arg is zero.

Notes

The value of the exponent returned by logb is always 1 less than the exponent retuned by frexp because of the different normalization requirements: for the exponent e returned by logb, |arg*r-e
| is between 1 and r (typically between 1 and 2), but for the exponent e returned by frexp, |arg*2-e
| is between 0.5 and 1.

See also

frexp	decomposes a number into significand and a power of 2 (function)
ilogb (C99)	extracts exponent of the number (function)
scalbn scalbln (C99) (C99)	multiplies a number by FLT_RADIX raised to a power (function)