143 lines
4.0 KiB
JavaScript
143 lines
4.0 KiB
JavaScript
/**
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* @license Apache-2.0
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*
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* Copyright (c) 2018 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var getSubscripts = require( './assign.js' );
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// MAIN //
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/**
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* Converts a linear index to an array of subscripts.
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*
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* ## Notes
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*
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* - The function accepts the following "modes":
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*
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* - `throw`: throws an error when a linear index exceeds array dimensions.
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* - `wrap`: wrap around a linear index exceeding array dimensions using modulo arithmetic.
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* - `clamp`: set a linear index exceeding array dimensions to either `0` (minimum linear index) or the maximum linear index.
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*
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* - When provided a stride array containing negative strides, if an `offset` is greater than `0`, the function interprets the linear index as an index into the underlying data buffer for the array, thus returning subscripts from the perspective of that buffer. If an `offset` is equal to `0`, the function treats the linear index as an index into an array view, thus returning subscripts from the perspective of that view.
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*
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* ```text
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* Dims: 2x2
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* Buffer: [ 1, 2, 3, 4 ]
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*
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* View = [ a00, a01,
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* a10, a11 ]
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*
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* Strides: 2,1
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* Offset: 0
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*
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* View = [ 1, 2,
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* 3, 4 ]
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*
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* Strides: 2,-1
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* Offset: 1
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*
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* View = [ 2, 1,
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* 4, 3 ]
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*
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* Strides: -2,1
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* Offset: 2
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*
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* View = [ 3, 4,
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* 1, 2 ]
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*
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* Strides: -2,-1
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* Offset: 3
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*
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* View = [ 4, 3,
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* 2, 1 ]
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* ```
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*
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* ```javascript
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* var shape = [ 2, 2 ];
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* var order = 'row-major';
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* var strides = [ -2, 1 ];
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* var offset = 2;
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* var mode = 'throw';
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*
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* // From the perspective of a view...
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* var s = ind2sub( shape, strides, 0, order, 0, mode );
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* // returns [ 0, 0 ]
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*
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* s = ind2sub( shape, strides, 0, order, 1, mode );
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* // returns [ 0, 1 ]
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*
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* s = ind2sub( shape, strides, 0, order, 2, mode );
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* // returns [ 1, 0 ]
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*
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* s = ind2sub( shape, strides, 0, order, 3, mode );
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* // returns [ 1, 1 ]
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*
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* // From the perspective of an underlying buffer...
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* s = ind2sub( shape, strides, offset, order, 0, mode );
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* // returns [ 1, 0 ]
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*
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* s = ind2sub( shape, strides, offset, order, 1, mode );
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* // returns [ 1, 1 ]
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*
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* s = ind2sub( shape, strides, offset, order, 2, mode );
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* // returns [ 0, 0 ]
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*
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* s = ind2sub( shape, strides, offset, order, 3, mode );
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* // returns [ 0, 1 ]
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* ```
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*
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* In short, from the perspective of a view, view data is always ordered.
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*
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*
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* @param {NonNegativeIntegerArray} shape - array shape
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* @param {IntegerArray} strides - stride array
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* @param {NonNegativeInteger} offset - location of the first indexed value **based** on the stride array
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* @param {string} order - specifies whether an array is row-major (C-style) or column-major (Fortran-style)
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* @param {integer} idx - linear index
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* @param {string} mode - specifies how to handle a linear index which exceeds array dimensions
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* @throws {RangeError} linear index must not exceed array dimensions
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* @returns {Array} subscripts
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*
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* @example
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* var shape = [ 3, 3, 3 ];
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* var strides = [ 9, 6, 1 ];
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* var offset = 0;
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* var order = 'row-major';
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*
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* var s = ind2sub( shape, strides, offset, order, 17, 'throw' );
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* // returns [ 1, 2, 2 ]
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*/
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function ind2sub( shape, strides, offset, order, idx, mode ) {
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var out;
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var i;
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out = [];
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for ( i = 0; i < shape.length; i++ ) {
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out.push( 0 );
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}
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return getSubscripts( shape, strides, offset, order, idx, mode, out );
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}
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// EXPORTS //
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module.exports = ind2sub;
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