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Template:ddcl list begin <tr class="t-dsc-header">

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

<td></td> <td></td> <tr class="t-dcl ">

<td >
float       logbf( float arg );
</td>

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

<td >
double      logb( double arg );
</td>

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

<td >
long double logbl( long double arg );
</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 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.

Contents

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.

Example

See also

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