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/**
* @license Apache-2.0
*
* Copyright (c) 2024 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 zeroTo = require( '@stdlib/array/base/zero-to' );
var reverse = require( '@stdlib/array/base/reverse' );
var take = require( '@stdlib/array/base/take-indexed' );
 
 
// MAIN //
 
/**
* Invokes a callback function once for each ndarray element.
*
* @private
* @param {Object} x - object containing ndarray meta data
* @param {ndarrayLike} x.ref - reference to the original ndarray-like object
* @param {string} x.dtype - data type
* @param {Collection} x.data - data buffer
* @param {NonNegativeIntegerArray} x.shape - dimensions
* @param {IntegerArray} x.strides - stride lengths
* @param {NonNegativeInteger} x.offset - index offset
* @param {string} x.order - specifies whether `x` is row-major (C-style) or column-major (Fortran-style)
* @param {Callback} fcn - callback function
* @param {*} thisArg - callback function execution context
* @returns {void}
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
* var naryFunction = require( '@stdlib/utils/nary-function' );
* var log = require( '@stdlib/console/log' );
*
* // Create a data buffer:
* var xbuf = new Float64Array( 8 );
*
* // Define the shape of the array:
* var shape = [ 2, 2 ];
*
* // Define the array strides:
* var sx = [ 4, 1 ];
*
* // Define the index offset:
* var ox = 1;
*
* // Create an ndarray-like object:
* var x = {
*     'ref': null,
*     'dtype': 'float64',
*     'data': xbuf,
*     'shape': shape,
*     'strides': sx,
*     'offset': ox,
*     'order': 'row-major'
* };
*
* // Apply the callback function:
* forEach2d( x, naryFunction( log, 1 ), {} );
*/
function forEach2d( x, fcn, thisArg ) {
	var xbuf;
	var dx0;
	var dx1;
	var idx;
	var sh;
	var S0;
	var S1;
	var sx;
	var ix;
	var i0;
	var i1;

	// Note on variable naming convention: S#, dx#, dy#, i# where # corresponds to the loop number, with `0` being the innermost loop...

	// Extract loop variables for purposes of loop interchange: dimensions and loop offset (pointer) increments...
	sh = x.shape;
	sx = x.strides;
	idx = zeroTo( sh.length );
	if ( x.order === 'row-major' ) {
		// For row-major ndarrays, the last dimensions have the fastest changing indices...
		S0 = sh[ 1 ];
		S1 = sh[ 0 ];
		dx0 = sx[ 1 ];                // offset increment for innermost loop
		dx1 = sx[ 0 ] - ( S0*sx[1] ); // offset increment for outermost loop
	} else { // order === 'column-major'
		// For column-major ndarrays, the first dimensions have the fastest changing indices...
		S0 = sh[ 0 ];
		S1 = sh[ 1 ];
		dx0 = sx[ 0 ];                // offset increment for innermost loop
		dx1 = sx[ 1 ] - ( S0*sx[0] ); // offset increment for outermost loop
		idx = reverse( idx );
	}
	// Set a pointer to the first indexed element:
	ix = x.offset;

	// Cache a reference to the output ndarray buffer:
	xbuf = x.data;

	// Iterate over the ndarray dimensions...
	for ( i1 = 0; i1 < S1; i1++ ) {
		for ( i0 = 0; i0 < S0; i0++ ) {
			fcn.call( thisArg, xbuf[ ix ], take( [ i1, i0 ], idx ), x.ref );
			ix += dx0;
		}
		ix += dx1;
	}
}
 
 
// EXPORTS //
 
module.exports = forEach2d;