logb

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ilogb (C99)
logb (C99)
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Macro constants
 
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.

Contents

[edit] Parameters

arg - floating point value

[edit] Return value

The floating-point exponent.

Domain or range error may occur if arg is zero.

[edit] 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.

[edit] Example

[edit] See also

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