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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 isColumnMajor = require( '@stdlib/ndarray/base/assert/is-column-major' );
var arraylike2object = require( '@stdlib/array/base/arraylike2object' );
var normalizeIndex = require( '@stdlib/ndarray/base/normalize-index' );
var gswap = require( '@stdlib/blas/base/gswap' ).ndarray;
var format = require( '@stdlib/string/format' );
var accessors = require( './accessors.js' );
// MAIN //
/**
* Interchanges two columns in a matrix `A` using alternative indexing semantics.
*
* ## Notes
*
* - If provided negative column indices, the function resolves the indices relative to the last column, with the last column corresponding to `-1`.
*
* @param {NonNegativeInteger} M - number of rows in matrix `A`
* @param {NonNegativeInteger} N - number of columns in matrix `A`
* @param {integer} i - index of the first column to interchange
* @param {integer} j - index of the second column to interchange
* @param {Collection} A - input matrix
* @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`
* @throws {RangeError} third argument must resolve to a valid column index
* @throws {RangeError} fourth argument must resolve to a valid column index
* @returns {Collection} `A`
*
* @example
* var A = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ]; // => [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ]
*
* gswapColumns( 3, 2, 0, 1, A, 2, 1, 0 );
* // A => [ 2.0, 1.0, 4.0, 3.0, 6.0, 5.0 ]
*/
function gswapColumns( M, N, i, j, A, strideA1, strideA2, offsetA ) {
var tmp;
var io;
var jo;
var oa;
var ia;
var ja;
var i1;
io = normalizeIndex( i, N-1 );
if ( io < 0 ) {
throw new RangeError( format( 'invalid argument. Third argument must resolve to a valid column index. Value: `%d`.', i ) );
}
jo = normalizeIndex( j, N-1 );
if ( jo < 0 ) {
throw new RangeError( format( 'invalid argument. Fourth argument must resolve to a valid column index. Value: `%d`.', j ) );
}
if ( io === jo ) {
return A;
}
if ( isColumnMajor( [ strideA1, strideA2 ] ) ) {
gswap( M, A, strideA1, offsetA+(io*strideA2), A, strideA1, offsetA+(jo*strideA2) ); // eslint-disable-line max-len
return A;
}
oa = arraylike2object( A );
if ( oa.accessorProtocol ) {
accessors( M, io, jo, oa, strideA1, strideA2, offsetA );
return A;
}
ia = offsetA + ( io*strideA2 );
ja = offsetA + ( jo*strideA2 );
for ( i1 = 0; i1 < M; i1++ ) {
tmp = A[ ia ];
A[ ia ] = A[ ja ];
A[ ja ] = tmp;
ia += strideA1;
ja += strideA1;
}
return A;
}
// EXPORTS //
module.exports = gswapColumns;
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