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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 gcusumors = require( '@stdlib/blas/ext/base/gcusumors' ).ndarray;
var arraylike2object = require( '@stdlib/array/base/arraylike2object' );
var isColumnMajor = require( '@stdlib/ndarray/base/assert/is-column-major' );
var accessors = require( './accessors.js' );
// MAIN //
/**
* Computes a summed-area table for a matrix using alternative indexing semantics.
*
* @param {PositiveInteger} M - number of rows in `A`
* @param {PositiveInteger} N - number of columns in `A`
* @param {NumericArray} A - input matrix
* @param {integer} strideA1 - stride length of first dimension of `A`
* @param {integer} strideA2 - stride length of second dimension of `A`
* @param {NonNegativeInteger} offsetA - starting index for `A`
* @param {NumericArray} out - output matrix
* @param {integer} strideOut1 - stride length of first dimension of `out`
* @param {integer} strideOut2 - stride length of second dimension of `out`
* @param {NonNegativeInteger} offsetOut - starting index for `out`
* @returns {NumericArray} output matrix
*
* @example
* var A = [ 1, 2, 3, 4 ];
* var out = [ 0, 0, 0, 0 ];
*
* gsummedAreaTable( 2, 2, A, 2, 1, 0, out, 2, 1, 0 );
* // out => [ 1, 3, 4, 10 ]
*/
function gsummedAreaTable( M, N, A, strideA1, strideA2, offsetA, out, strideOut1, strideOut2, offsetOut ) { // eslint-disable-line max-len
var oa;
var oo;
var ia;
var io;
var i;
var j;
if ( M <= 0 || N <= 0 ) {
return out;
}
oa = arraylike2object( A );
oo = arraylike2object( out );
if ( oa.accessorProtocol || oo.accessorProtocol ) {
return accessors( M, N, oa, strideA1, strideA2, offsetA, oo, strideOut1, strideOut2, offsetOut ); // eslint-disable-line max-len
}
// Compute cumulative sum of first row:
gcusumors( N, 0.0, A, strideA2, offsetA, out, strideOut2, offsetOut );
// Compute cumulative sum of first column:
gcusumors( M - 1, out[ offsetOut ], A, strideA1, offsetA + strideA1, out, strideOut1, offsetOut + strideOut1 ); // eslint-disable-line max-len
// Process remaining elements...
if ( isColumnMajor( [ strideOut1, strideOut2 ] ) ) { // Column-major
for ( j = 1; j < N; j++ ) {
for ( i = 1; i < M; i++ ) {
ia = offsetA + ( i * strideA1 );
io = offsetOut + ( i * strideOut1 );
out[ io + ( j * strideOut2 ) ] = A[ ia + ( j * strideA2 ) ] +
out[ io + ( ( j - 1 ) * strideOut2 ) ] +
out[ ( io - strideOut1 ) + ( j * strideOut2 ) ] -
out[ ( io - strideOut1 ) + ( ( j - 1 ) * strideOut2 ) ];
}
}
} else { // Row-major
for ( i = 1; i < M; i++ ) {
ia = offsetA + ( i * strideA1 );
io = offsetOut + ( i * strideOut1 );
for ( j = 1; j < N; j++ ) {
out[ io + ( j * strideOut2 ) ] = A[ ia + ( j * strideA2 ) ] +
out[ io + ( ( j - 1 ) * strideOut2 ) ] +
out[ ( io - strideOut1 ) + ( j * strideOut2 ) ] -
out[ ( io - strideOut1 ) + ( ( j - 1 ) * strideOut2 ) ];
}
}
}
return out;
}
// EXPORTS //
module.exports = gsummedAreaTable;
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