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* @license Apache-2.0
*
* Copyright (c) 2026 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.
*/
'use strict';
// MODULES //
var isnan = require( '@stdlib/math/base/assert/is-nan' );
var f16 = require( '@stdlib/number/float64/base/to-float16' );
var ulpdiff = require( '@stdlib/number/float16/base/ulp-difference' );
// MAIN //
/**
* Tests if two half-precision floating-point numbers are approximately the same value within a specified number of ULPs (units in the last place).
*
* ## Notes
*
* - The function implements the [SameValue Algorithm][ecma-262-same-value-algorithm], as specified in ECMAScript 5.
* - In contrast to the strict equality operator `===`, `-0` and `+0` are distinguishable and `NaNs` are the same.
*
* [ecma-262-same-value-algorithm]: http://ecma-international.org/ecma-262/5.1/#sec-9.12
*
* @param {number} a - first input value
* @param {number} b - second input value
* @param {number} maxULP - maximum allowed ULP difference
* @returns {boolean} boolean indicating whether two half-precision floating-point numbers are approximately the same value within a specified number of ULPs
*
* @example
* var EPS = require( '@stdlib/constants/float16/eps' );
*
* var bool = isAlmostSameValue( 1.0, 1.0+EPS, 1 );
* // returns true
*
* bool = isAlmostSameValue( 1.0+EPS, 1.0, 1 );
* // returns true
*
* bool = isAlmostSameValue( 1.0, 1.0+EPS+EPS, 1 );
* // returns false
*
* bool = isAlmostSameValue( 1.0, 1.0+EPS, 0 );
* // returns false
*
* bool = isAlmostSameValue( 0.0, -0.0, 0 );
* // returns false
*
* bool = isAlmostSameValue( 1.0, NaN, 1 );
* // returns false
*
* bool = isAlmostSameValue( NaN, NaN, 1 );
* // returns true
*/
function isAlmostSameValue( a, b, maxULP ) {
var af;
var bf;
af = f16( a );
bf = f16( b );
// Check for NaN (NaN is considered equal to NaN in SameValue):
if ( isnan( af ) && isnan( bf ) ) {
return true;
}
// Only distinguish signed zeros when maxULP is 0:
if ( maxULP === 0 && af === 0.0 && bf === 0.0 ) {
return ( 1.0 / af === 1.0 / bf );
}
// Check if exactly equal:
if ( af === bf ) {
return true;
}
// Check ULP difference:
return ulpdiff( af, bf ) <= maxULP;
}
// EXPORTS //
module.exports = isAlmostSameValue;
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