std::logb

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Defined in header <cmath>

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float       logb( float arg );

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double      logb( double arg );

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long double logb( long double arg );

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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 logr|arg| as a signed floating-point value, for non-zero arg, where r is Template:cpp and T is the floating-point type of arg. If arg is subnormal, it is treated as though it was normalized.

Parameters

arg

-

floating point value

Notes

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

Return value

The floating-point exponent.

Domain or range error may occur if arg is zero.

See also

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