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* @license Apache-2.0
*
* Copyright (c) 2025 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*
* ## Notice
*
* The following copyright and license were part of the original implementation available as part of [FreeBSD]{@link https://svnweb.freebsd.org/base/release/12.2.0/lib/msun/src/e_log2f.c}. The implementation follows the original, but has been modified for JavaScript.
*
* ```text
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ```
*/
'use strict';
// MODULES //
var isnanf = require( '@stdlib/math/base/assert/is-nanf' );
var f32 = require( '@stdlib/number/float64/base/to-float32' );
var toWordf = require( '@stdlib/number/float32/base/to-word' );
var fromWordf = require( '@stdlib/number/float32/base/from-word' );
var ABS_MASK = require( '@stdlib/constants/float32/abs-mask' );
var FLOAT32_EXPONENT_BIAS = require( '@stdlib/constants/float32/exponent-bias' );
var FLOAT32_SIGNIFICAND_MASK = require( '@stdlib/constants/float32/significand-mask' );
var NINF = require( '@stdlib/constants/float32/ninf' );
var kernelLog1pf = require( '@stdlib/math/base/special/kernel-log1pf' );
// VARIABLES //
var TWO25 = f32( 3.3554432000e+07 ); // 0x4c000000
var IVLN2HI = f32( 1.4428710938e+00 ); /* 0x3fb8b000 */
var IVLN2LO = f32( -1.7605285393e-04 ); // 0x3de705fc, 0x2eefa200
var HIGH_MAX_NORMAL_EXP = 0x7f800000|0; // asm type annotation
var HIGH_MIN_NORMAL_EXP = 0x00800000|0; // asm type annotation
var HIGH_BIASED_EXP_0 = 0x3f800000|0; // asm type annotation
// MAIN //
/**
* Evaluates the binary logarithm (base two) for single-precision floating point values.
*
* @param {NonNegativeNumber} x - input value
* @returns {number} function value
*
* @example
* var v = log2f( 4.0 );
* // returns 2.0
*
* @example
* var v = log2f( 8.0 );
* // returns 3.0
*
* @example
* var v = log2f( 0.0 );
* // returns -Infinity
*
* @example
* var v = log2f( Infinity );
* // returns Infinity
*
* @example
* var v = log2f( NaN );
* // returns NaN
*
* @example
* var v = log2f( -4.0 );
* // returns NaN
*/
function log2f( x ) {
var hfsq;
var hi;
var hx;
var lo;
var f;
var R;
var y;
var i;
var k;
if ( isnanf( x ) || x < 0.0 ) {
return NaN;
}
if ( x === 0.0 ) {
return NINF;
}
x = f32( x );
hx = toWordf( x ) | 0;
k = 0|0; // asm type annotation
if ( hx < HIGH_MIN_NORMAL_EXP ) {
// Case: x < 2**-126
if ( hx&ABS_MASK === 0 ) {
return NINF;
}
k -= 25|0; // asm type annotation
// Subnormal number, scale up x:
x = f32( x * TWO25 );
hx = toWordf( x ) | 0;
}
if ( hx >= HIGH_MAX_NORMAL_EXP ) {
return f32( x + x );
}
// Case: log(1) = +0
if ( hx === HIGH_BIASED_EXP_0 ) {
return 0.0;
}
k = f32( k + f32( ( ( hx >> 23 ) - FLOAT32_EXPONENT_BIAS ) | 0 ) );
hx &= FLOAT32_SIGNIFICAND_MASK;
i = f32( ( ( hx+0x4afb0d ) & HIGH_MIN_NORMAL_EXP )|0 ); // asm type annotation
// Normalize x or x/2...
x = fromWordf( hx | ( i ^ HIGH_BIASED_EXP_0) );
k = f32( k + ( ( i >> 23 ) | 0 ) );
y = f32( k );
f = f32( x - 1.0 );
hfsq = f32( 0.5 * f32( f * f ) );
R = kernelLog1pf( f );
hi = f32( f - hfsq );
hx = toWordf( hi ) | 0;
hi = fromWordf( hx & 0xfffff000);
lo = f32( f32( f - hi ) - f32( hfsq ) + f32( R ) );
return f32( f32( f32( lo + hi ) * IVLN2LO ) + f32( lo * IVLN2HI ) + f32( hi * IVLN2HI ) + f32( y ) ); // eslint-disable-line max-len
}
// EXPORTS //
module.exports = log2f;
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