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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 gfill = require( '@stdlib/blas/ext/base/gfill' ).ndarray;
var min = require( '@stdlib/math/base/special/fast/min' );
// MAIN //
/**
* Fills the anti-diagonal of a matrix with a specified scalar constant using alternative indexing semantics.
*
* @param {PositiveInteger} M - number of rows in `A`
* @param {PositiveInteger} N - number of columns in `A`
* @param {integer} k - starting index for the anti-diagonal
* @param {*} alpha - scalar constant
* @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`
* @returns {Collection} input matrix
*
* @example
* var A = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
*
* gfillAntiDiagonal( 2, 3, 0, 7.0, A, 3, 1, 0 );
* // A => [ 1.0, 2.0, 7.0, 4.0, 7.0, 6.0 ]
*
* @example
* var A = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
*
* gfillAntiDiagonal( 2, 3, 1, 8.0, A, 3, 1, 0 );
* // A => [ 1.0, 8.0, 3.0, 8.0, 5.0, 6.0 ]
*
* @example
* var A = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
*
* gfillAntiDiagonal( 2, 3, -1, 9.0, A, 3, 1, 0 );
* // A => [ 1.0, 2.0, 3.0, 4.0, 5.0, 9.0 ]
*
* @example
* var A = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ];
*
* gfillAntiDiagonal( 2, 3, 0, 10.0, A, 4, 1, 5 );
* // A => [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 10.0, 9.0, 10.0, 10.0, 12.0 ]
*/
function gfillAntiDiagonal( M, N, k, alpha, A, strideA1, strideA2, offsetA ) {
var dStride;
var offset;
var nDiag;
if ( M <= 0 || N <= 0 ) {
return A;
}
// Determine the number of elements on the anti-diagonal...
if ( k >= 0 ) {
nDiag = min( M, N - k );
offset = offsetA + ( ( N - 1 - k ) * strideA2 );
} else {
nDiag = min( M + k, N );
offset = offsetA - ( k * strideA1 ) + ( ( N - 1 ) * strideA2 );
}
if ( nDiag <= 0 ) {
return A;
}
// The anti-diagonal stride moves down one row and left one column:
dStride = strideA1 - strideA2;
// Fill the anti-diagonal:
return gfill( nDiag, alpha, A, dStride, offset );
}
// EXPORTS //
module.exports = gfillAntiDiagonal;
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