libm.info: ilogb

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`ilogb', `ilogbf'--get exponent of floating point number

*Synopsis*
     #include <math.h>
     int ilogb(double VAL);
     int ilogbf(float VAL);
   *Description*
All non zero, normal numbers can be described as M * 2**P.  `ilogb' and
`ilogbf' examine the argument VAL, and return P.  The functions `frexp'
and `frexpf' are similar to `ilogb' and `ilogbf', but also return M.
*Returns*
`ilogb' and `ilogbf' return the power of two used to form the floating
point argument.  If VAL is `0', they return `- INT_MAX' (`INT_MAX' is
defined in limits.h).  If VAL is infinite, or NaN, they return
`INT_MAX'.
*Portability*
Neither `ilogb' nor `ilogbf' is required by ANSI C or by the System V
Interface Definition (Issue 2).