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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 isColumnMajor = require( '@stdlib/ndarray/base/assert/is-column-major' );
// MAIN //
/**
* Computes a summed-area table for a matrix using accessor arrays.
*
* @private
* @param {PositiveInteger} M - number of rows in `A`
* @param {PositiveInteger} N - number of columns in `A`
* @param {Object} A - input matrix object
* @param {Collection} A.data - input matrix data
* @param {Array<Function>} A.accessors - array element accessors
* @param {integer} strideA1 - stride length for first dimension of `A`
* @param {integer} strideA2 - stride length for second dimension of `A`
* @param {NonNegativeInteger} offsetA - starting index for `A`
* @param {Object} out - output matrix object
* @param {Collection} out.data - output matrix data
* @param {Array<Function>} out.accessors - array element accessors
* @param {integer} strideOut1 - stride length for first dimension of `out`
* @param {integer} strideOut2 - stride length for second dimension of `out`
* @param {NonNegativeInteger} offsetOut - starting index for `out`
* @returns {Object} output matrix object
*
* @example
* var toAccessorArray = require( '@stdlib/array/base/to-accessor-array' );
* var arraylike2object = require( '@stdlib/array/base/arraylike2object' );
*
* var A = [ 1, 2, 3, 4 ];
* var out = [ 0, 0, 0, 0 ];
*
* accessors( 2, 2, arraylike2object( toAccessorArray( A ) ), 2, 1, 0, arraylike2object( toAccessorArray( out ) ), 2, 1, 0 );
* // out => [ 1, 3, 4, 10 ]
*/
function accessors( M, N, A, strideA1, strideA2, offsetA, out, strideOut1, strideOut2, offsetOut ) { // eslint-disable-line max-len
var obuf;
var oset;
var oget;
var abuf;
var aget;
var io;
var ia;
var i;
var j;
var v;
// Cache references to array data:
abuf = A.data;
obuf = out.data;
// Cache references to element accessors:
aget = A.accessors[ 0 ];
oget = out.accessors[ 0 ];
oset = out.accessors[ 1 ];
// Compute cumulative sum of first row:
gcusumors( N, 0.0, abuf, strideA2, offsetA, obuf, strideOut2, offsetOut );
// Compute cumulative sum of first column:
gcusumors( M - 1, oget( obuf, offsetOut ), abuf, strideA1, offsetA + strideA1, obuf, 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 );
v = aget( abuf, ia + ( j * strideA2 ) ) +
oget( obuf, io + ( ( j - 1 ) * strideOut2 ) ) +
oget( obuf, ( io - strideOut1 ) + ( j * strideOut2 ) ) -
oget( obuf, ( io - strideOut1 ) + ( ( j - 1 ) * strideOut2 ) ); // eslint-disable-line max-len
oset( obuf, io + ( j * strideOut2 ), v );
}
}
return out;
}
// Row-major
for ( i = 1; i < M; i++ ) {
ia = offsetA + ( i * strideA1 );
io = offsetOut + ( i * strideOut1 );
for ( j = 1; j < N; j++ ) {
v = aget( abuf, ia + ( j * strideA2 ) ) +
oget( obuf, io + ( ( j - 1 ) * strideOut2 ) ) +
oget( obuf, ( io - strideOut1 ) + ( j * strideOut2 ) ) -
oget( obuf, ( io - strideOut1 ) + ( ( j - 1 ) * strideOut2 ) );
oset( obuf, io + ( j * strideOut2 ), v );
}
}
return out;
}
// EXPORTS //
module.exports = accessors;
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