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* @license Apache-2.0
*
* Copyright (c) 2023 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 float64ToFloat32 = require( '@stdlib/number/float64/base/to-float32' );
var absf = require( '@stdlib/math/base/special/absf' );
var sqrtf = require( '@stdlib/math/base/special/sqrtf' );
var abs2f = require( '@stdlib/math/base/special/abs2f' );
var copysignf = require( '@stdlib/math/base/special/copysignf' );
// MAIN //
/**
* Constructs a Givens plane rotation using alternative indexing semantics.
*
* @param {number} a - rotational elimination parameter
* @param {number} b - rotational elimination parameter
* @param {Float32Array} out - output array
* @param {integer} strideOut - stride length for `Out`
* @param {NonNegativeInteger} offsetOut - starting index for `Out`
* @returns {Float32Array} output array
*
* @example
* var Float32Array = require( '@stdlib/array/float32' );
*
* var out = srotg( 0.0, 2.0, new Float32Array( 4 ), 1, 0 );
* // returns <Float32Array>[ 2.0, 1.0, 0.0, 1.0 ]
*/
function srotg( a, b, out, strideOut, offsetOut ) {
var scale;
var sign;
var aa;
var ab;
var r;
var c;
var s;
var z;
aa = absf( a );
ab = absf( b );
if ( aa > ab ) {
sign = copysignf( 1.0, a );
} else {
sign = copysignf( 1.0, b );
}
scale = float64ToFloat32( aa + ab );
if ( scale === 0.0 ) {
c = 1.0;
s = 0.0;
r = 0.0;
z = 0.0;
} else {
r = float64ToFloat32( scale * sqrtf( float64ToFloat32( abs2f( float64ToFloat32( a/scale ) ) + abs2f( float64ToFloat32( b/scale ) ) ) ) ); // eslint-disable-line max-len
r = float64ToFloat32( r * sign );
c = float64ToFloat32( a / r );
s = float64ToFloat32( b / r );
z = 1.0;
if ( aa > ab ) {
z = s;
} else if ( c !== 0.0 ) {
z = float64ToFloat32( 1.0 / c );
}
}
a = r;
b = z;
out[ offsetOut ] = a;
out[ offsetOut + strideOut ] = b;
out[ offsetOut + ( 2 * strideOut ) ] = c;
out[ offsetOut + ( 3 * strideOut ) ] = s;
return out;
}
// EXPORTS //
module.exports = srotg;
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