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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';
// MAIN //
/**
* Interchanges two rows of a matrix.
*
* @private
* @param {PositiveInteger} M - number of rows in `A`
* @param {PositiveInteger} N - number of columns in `A`
* @param {NonNegativeInteger} i - index of the first row to interchange
* @param {NonNegativeInteger} j - index of the second row to interchange
* @param {Object} A - input matrix object
* @param {Collection} A.data - input matrix data
* @param {Array<Function>} A.accessors - matrix element accessors
* @param {integer} strideA1 - stride length for the first dimension of `A`
* @param {integer} strideA2 - stride length for the second dimension of `A`
* @param {NonNegativeInteger} offsetA - starting index for `A`
* @returns {void}
*
* @example
* var toAccessorArray = require( '@stdlib/array/base/to-accessor-array' );
* var arraylike2object = require( '@stdlib/array/base/arraylike2object' );
*
* var A = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ]; // => [ [ 1.0, 4.0 ], [ 2.0, 5.0 ], [ 3.0, 6.0 ] ]
*
* gswapRows( 3, 2, 0, 2, arraylike2object( toAccessorArray( A ) ), 1, 3, 0 );
* // A => [ 3.0, 2.0, 1.0, 6.0, 5.0, 4.0 ]
*/
function gswapRows( M, N, i, j, A, strideA1, strideA2, offsetA ) {
var abuf;
var aget;
var aset;
var da0;
var da1;
var S0;
var S1;
var vi;
var vj;
var pi;
var pj;
var ia;
var i0;
var i1;
// Cache references to array data:
abuf = A.data;
// Cache references to the element accessors:
aget = A.accessors[ 0 ];
aset = A.accessors[ 1 ];
// Column-major...
S0 = M;
S1 = N;
// Resolve loop offsets:
da0 = strideA1;
da1 = strideA2 - ( S0*strideA1 );
ia = offsetA;
for ( i1 = 0; i1 < S1; i1++ ) {
// Scan down the rows in a column to find elements at rows `i` and `j`...
for ( i0 = 0; i0 < S0; i0++ ) {
if ( i0 === i ) {
vi = aget( abuf, ia );
pi = ia;
}
if ( i0 === j ) {
vj = aget( abuf, ia );
pj = ia;
}
ia += da0;
}
aset( abuf, pi, vj );
aset( abuf, pj, vi );
ia += da1;
}
}
// EXPORTS //
module.exports = gswapRows;
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