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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.
*
*
* ## Notice
*
* The original C code, long comment, copyright, license, and constants are from [Cephes]{@link http://www.netlib.org/cephes}. The implementation follows the original, but has been modified for JavaScript.
*
* ```text
* Copyright 1985, 1995, 2000 by Stephen L. Moshier
*
* Some software in this archive may be from the book _Methods and Programs for Mathematical Functions_ (Prentice-Hall or Simon & Schuster International, 1989) or from the Cephes Mathematical Library, a commercial product. In either event, it is copyrighted by the author. What you see here may be used freely but it comes with no support or guarantee.
*
* Stephen L. Moshier
* moshier@na-net.ornl.gov
* ```
*/
'use strict';
// MODULES //
var isnanf = require( '@stdlib/math/base/assert/is-nanf' );
var isInfinitef = require( '@stdlib/math/base/assert/is-infinitef' );
var exp = require( '@stdlib/math/base/special/exp' );
var f32 = require( '@stdlib/number/float64/base/to-float32' );
var PINF = require( '@stdlib/constants/float32/pinf' );
var MAXLOGF = require( '@stdlib/constants/float32/max-ln' );
// VARIABLES //
var ZERO = f32( 0.0 );
var HALF = f32( 0.5 );
var ONE = f32( 1.0 );
var TWO = f32( 2.0 );
// MAIN //
/**
* Computes the hyperbolic cosine of a single-precision floating-point number.
*
* ## Method
*
* ```tex
* \operatorname{coshf}(x) = \frac{ \exp(x) + \exp(-x) }{2}
* ```
*
* ## Notes
*
* - Relative error:
*
* | arithmetic | domain | # trials | peak | rms |
* |:----------:|:---------:|:--------:|:-------:|:-------:|
* | IEEE | +-MAXLOGF | 100000 | 1.2e-7 | 2.8e-8 |
*
* @param {number} x - input value
* @returns {number} hyperbolic cosine
*
* @example
* var v = coshf( 0.0 );
* // returns 1.0
*
* @example
* var v = coshf( 2.0 );
* // returns ~3.762
*
* @example
* var v = coshf( -2.0 );
* // returns ~3.762
*
* @example
* var v = coshf( NaN );
* // returns NaN
*/
function coshf( x ) {
var z;
if ( isnanf( x ) ) {
return x;
}
if ( x < ZERO ) {
x = -x;
}
// Handle infinities:
if ( isInfinitef( x ) ) {
return PINF;
}
// Avoid premature overflow by evaluating `exp(x/2) * exp(x/2) / 2`:
if ( x >= MAXLOGF ) {
z = f32( exp( f32( HALF * x ) ) );
return f32( f32( HALF * z ) * z );
}
z = f32( exp( f32( x ) ) );
z = f32( z + ( ONE/z ) );
return f32( z / TWO );
}
// EXPORTS //
module.exports = coshf;
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