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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 sqrt = require( '@stdlib/math/base/special/sqrt' );
var abs = require( '@stdlib/math/base/special/abs' );
var max = require( '@stdlib/math/base/special/max' );
var dlamch = require( '@stdlib/lapack/base/dlamch' );
var trunc = require( '@stdlib/math/base/special/trunc' );
var pow = require( '@stdlib/math/base/special/pow' );
var ln = require( '@stdlib/math/base/special/ln' );
// MAIN //
/**
* Generates a plane rotation so that the diagonal is nonnegative.
* @private
* @param {number} F - the first component of vector to be rotated.
* @param {number} G - the second component of vector to be rotated.
* @param {Float64Array} out - output array containing the cosine and sine of the rotation and the non zero component of the rotated vector.
* @param {integer} strideOut - stride length for `out`
* @param {NonNegativeInteger} offsetOut - starting index of `out`
* @returns {Float64Array} output array
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var out = new Float64Array( 3 );
* dlartgp( 1.0, 2.0, out, 1, 0 );
* // out => <Float64Array>[ ~0.447, ~0.894, ~2.236 ]
*/
function dlartgp( F, G, out, strideOut, offsetOut ) {
var safmin;
var safmn2;
var safmx2;
var count;
var scale;
var base;
var eps;
var cs;
var f1;
var g1;
var sn;
var f;
var g;
var r;
f=F;
g=G;
safmin = dlamch( 'S' );
eps = dlamch( 'E' );
base = dlamch( 'B' );
safmn2 = pow( base, trunc( ln( safmin / eps ) / ln( base ) / 2.0 ));
safmx2 = 1.0 / safmn2;
if ( g === 0.0 ) {
cs = ( f >= 0.0 ) ? 1.0 : -1.0;
sn = 0.0;
r = abs( f );
} else if ( f === 0.0 ) {
cs = 0.0;
sn = ( g >= 0.0 ) ? 1.0 : -1.0;
r = abs( g );
} else {
f1 = f;
g1 = g;
scale = max( abs( f1 ), abs( g1 ) );
if ( scale >= safmx2 ) {
count = 0;
while ( scale >= safmx2 && count < 20 ) {
count += 1;
f1 *= safmn2;
g1 *= safmn2;
scale = max( abs( f1 ), abs( g1 ) );
}
r = sqrt( ( f1*f1 ) + ( g1*g1 ) );
cs = f1 / r;
sn = g1 / r;
while ( count > 0 ) {
r *= safmx2;
count -= 1;
}
} else if ( scale <= safmn2 ) {
count = 0;
while ( scale <= safmn2 ) {
count += 1;
f1 *= safmx2;
g1 *= safmx2;
scale = max( abs( f1 ), abs( g1 ) );
}
r = sqrt( ( f1*f1 ) + ( g1*g1 ) );
cs = f1 / r;
sn = g1 / r;
while ( count > 0 ) {
r *= safmn2;
count -= 1;
}
} else {
r = sqrt( ( f1*f1 ) + ( g1*g1 ) );
cs = f1 / r;
sn = g1 / r;
}
}
if ( r < 0.0 ) {
cs *= -1;
sn *= -1;
r *= -1;
}
out[ offsetOut ] = cs;
out[ offsetOut + strideOut ] = sn;
out[ offsetOut + ( strideOut*2 ) ] = r;
return out;
}
// EXPORTS //
module.exports = dlartgp;
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