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* @license Apache-2.0
*
* Copyright (c) 2025 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 isRowMajor = require( '@stdlib/ndarray/base/assert/is-row-major' );
var max = require( '@stdlib/math/base/special/max' );
// MAIN //
/**
* Finds the index of the last non zero row in a matrix `A`.
*
* @private
* @param {PositiveInteger} M - number of rows in `A`
* @param {PositiveInteger} N - number of columns in `A`
* @param {Float64Array} A - input matrix
* @param {integer} strideA1 - stride of the first dimension of `A`
* @param {integer} strideA2 - stride of the second dimension of `A`
* @param {NonNegativeInteger} offsetA - index offset for `A`
* @returns {integer} index of the last row
*
* @example
* var Float64array = require( '@stdlib/array/float64' );
*
* var A = new Float64array( [ 1.0, 2.0, 3.0, 4.0, 0.0, 0.0 ] ); // => [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 0.0, 0.0 ] ]
*
* var out = iladlr( 3, 2, A, 2, 1, 0 );
* // returns 1
*/
function iladlr( M, N, A, strideA1, strideA2, offsetA ) {
var iladlr;
var ia1;
var ia2;
var i;
var j;
if ( M === 0 || N === 0 ) {
return -1; // Invalid index
}
ia1 = offsetA + ( (M-1) * strideA1 ); // A( M, 1 )
ia2 = ia1 + ( (N-1) * strideA2 ); // A( M, N )
// Quick test for common case where corners are non-zero:
if ( A[ ia1 ] !== 0.0 || A[ ia2 ] !== 0.0 ) {
return M - 1;
}
if ( isRowMajor( [ strideA1, strideA2 ] ) ) {
ia1 = offsetA + ( (M-1) * strideA1 ); // Tracks rows
for ( i = M - 1; i >= 0; i-- ) {
ia2 = 0; // Tracks columns
for ( j = 0; j < N; j++ ) {
if ( A[ ia1 + ia2 ] !== 0.0 ) { // Find the last row with a non-zero entry
return i;
}
ia2 += strideA2;
}
ia1 -= strideA1;
}
// If we reach here, then all entries in the matrix are zero, return -1 (invalid index)
iladlr = -1;
} else {
ia2 = offsetA; // Tracks columns
iladlr = -1; // initialize iladlr, will return -1 (invalid index) if all entries are zero
for ( j = 0; j < N; j++ ) {
i = M - 1;
ia1 = (M-1) * strideA1; // Tracks rows
while ( A[ ia1 + ia2 ] === 0.0 && i >= 0 ) {
i -= 1;
ia1 -= strideA1;
}
iladlr = max( i, iladlr );
ia2 += strideA2;
}
}
return iladlr;
}
// EXPORTS //
module.exports = iladlr;
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