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ilogb

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Defined in header <math.h>
</td>

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<td >
int ilogbf( float arg );
</td>

<td class="t-dcl-nopad"> </td> <td > (since C99) </td> </tr> <tr class="t-dcl ">

<td >
int ilogb( double arg );
</td>

<td class="t-dcl-nopad"> </td> <td > (since C99) </td> </tr> <tr class="t-dcl ">

<td >
int ilogbl( long double arg );
</td>

<td class="t-dcl-nopad"> </td> <td > (since C99) </td> </tr> <tr class="t-dcl ">

<td >
#define FP_ILOGB0 /*implementation-defined*/
</td>

<td class="t-dcl-nopad"> </td> <td > (since C99) </td> </tr> <tr class="t-dcl ">

<td >
#define FP_ILOGBNAN /*implementation-defined*/
</td>

<td class="t-dcl-nopad"> </td> <td > (since C99) </td> </tr> Template:ddcl list end

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

Contents

Parameters

arg - floating point value

Return value

The floating-point exponent, cast to integer.

Domain or range error may occur if arg is zero, FP_ILOGB0 is returned in that case.

Domain or range error may occur if arg is infinite, MAX_INT is returned in that case.

Domain or range error may occur if arg is NaN, FP_ILOGBNAN is returned in that case.

If the result cannot be represented as int, the result is undefined.

Notes

The value of the exponent returned by ilogb is always 1 less than the exponent retuned by frexp because of the different normalization requirements: for the exponent e returned by ilogb, |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.

Example

See also

Template:c/numeric/math/dcl list frexpTemplate:c/numeric/math/dcl list logbTemplate:c/numeric/math/dcl list scalbn