Binary Logarithm

Evaluate the binary logarithm.

The binary logarithm (logarithm with base 2) is defined for any positive real number as

$$\quad \log_{2} \left( x \right) = y \quad \text{such that} \quad 2^y = x$$

Usage

var log2 = require( '@stdlib/math/base/special/log2' );

log2( x )

Evaluates the binary logarithm.

var v = log2( 4.0 );
// returns 2.0

v = log2( 0.0 );
// returns -Infinity

v = log2( Infinity );
// returns Infinity

v = log2( NaN );
// returns NaN

For negative numbers, the binary logarithm is not defined.

var v = log2( -4.0 );
// returns NaN

Examples

var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var logEachMap = require( '@stdlib/console/log-each-map' );
var log2 = require( '@stdlib/math/base/special/log2' );

var opts = {
    'dtype': 'float64'
};
var x = discreteUniform( 100, 0, 100, opts );

logEachMap( 'log2(%d) = %0.4f', x, log2 );

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C APIs

Usage

#include "stdlib/math/base/special/log2.h"

stdlib_base_log2( x )

Evaluates the binary logarithm.

double out = stdlib_base_log2( 4.0 );
// returns 2.0

The function accepts the following arguments:

• x: [in] double input value.

double stdlib_base_log2( const double x );

Examples

#include "stdlib/math/base/special/log2.h"
#include <stdlib.h>
#include <stdio.h>

int main( void ) {
    double x;
    double v;
    int i;
    for ( i = 0; i < 100; i++ ) {
        x = ( ( (double)rand() / (double)RAND_MAX ) * 100.0 );
        v = stdlib_base_log( x );
        printf( "log2(%lf) = %lf\n", x, v );
    }
}

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See Also

• @stdlib/math/base/special/exp2: base 2 exponential function.
• @stdlib/math/base/special/ln: evaluate the natural logarithm of a double-precision floating-point number.
• @stdlib/math/base/special/log: compute the base b logarithm of a double-precision floating-point number.