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* @license Apache-2.0
*
* Copyright (c) 2018 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 format = require( '@stdlib/string/format' );
// MAIN //
/**
* Converts subscripts to a linear index.
*
* ## Notes
*
* - The function accepts the following "modes":
*
* - **throw**: throw an error when a subscript exceeds array dimensions.
* - **normalize**: normalize negative subscripts and throw an error when a subscript exceeds array dimensions.
* - **wrap**: wrap around subscripts exceeding array dimensions using modulo arithmetic.
* - **clamp**: set subscripts exceeding array dimensions to either `0` (minimum index) or the maximum index along a particular dimension.
*
* - When provided fewer modes than dimensions, the function recycles modes using modulo arithmetic.
*
* - When provided a stride array containing negative strides, if an `offset` is greater than `0`, the function treats subscripts as mapping to a linear index in an underlying data buffer for the array, thus returning a linear index from the perspective of that buffer. If an `offset` is equal to `0`, the function treats subscripts as mapping to a linear index in an array view, thus returning a linear index from the perspective of that view.
*
* ```text
* Dims: 2x2
* Buffer: [ 1, 2, 3, 4 ]
*
* View = [ a00, a01,
* a10, a11 ]
*
* Strides: 2,1
* Offset: 0
*
* View = [ 1, 2,
* 3, 4 ]
*
* Strides: 2,-1
* Offset: 1
*
* View = [ 2, 1,
* 4, 3 ]
*
* Strides: -2,1
* Offset: 2
*
* View = [ 3, 4,
* 1, 2 ]
*
* Strides: -2,-1
* Offset: 3
*
* View = [ 4, 3,
* 2, 1 ]
* ```
*
* ```javascript
* var shape = [ 2, 2 ];
* var strides = [ -2, 1 ];
* var offset = 2;
* var mode = [ 'throw' ];
*
* // From the perspective of a view...
* var idx = sub2ind( shape, strides, 0, 0, 0, mode );
* // returns 0
*
* idx = sub2ind( shape, strides, 0, 0, 1, mode );
* // returns 1
*
* idx = sub2ind( shape, strides, 0, 1, 0, mode );
* // returns 2
*
* idx = sub2ind( shape, strides, 0, 1, 1, mode );
* // returns 3
*
* // From the perspective of an underlying buffer...
* idx = sub2ind( shape, strides, offset, 0, 0, mode );
* // returns 2
*
* idx = sub2ind( shape, strides, offset, 0, 1, mode );
* // returns 3
*
* idx = sub2ind( shape, strides, offset, 1, 0, mode );
* // returns 0
*
* idx = sub2ind( shape, strides, offset, 1, 1, mode );
* // returns 1
* ```
*
* In short, from the perspective of a view, view data is always ordered.
*
* @param {NonNegativeIntegerArray} shape - array shape
* @param {IntegerArray} strides - stride array
* @param {NonNegativeInteger} offset - location of the first indexed value **based** on the stride array
* @param {...integer} i - subscripts
* @param {StringArray} mode - specifies how to handle subscripts which exceed array dimensions
* @throws {RangeError} must provide subscripts which do not exceed array dimensions
* @returns {NonNegativeInteger} linear index
*
* @example
* var shape = [ 3, 3, 3 ];
* var strides = [ 9, 3, 1 ];
* var offset = 0;
* var mode = [ 'throw' ]
*
* var idx = sub2ind( shape, strides, offset, 1, 2, 2, mode );
* // returns [ 'throw' ]
*/
function sub2ind() {
var strides;
var offset;
var nmodes;
var shape;
var ndims;
var modes;
var mode;
var idx;
var m;
var s;
var j;
var i;
shape = arguments[ 0 ];
strides = arguments[ 1 ];
offset = arguments[ 2 ];
ndims = shape.length;
modes = arguments[ 3+ndims ]; // last argument
nmodes = modes.length;
idx = offset;
for ( i = 0; i < ndims; i++ ) {
m = shape[ i ];
j = arguments[ i+3 ];
mode = modes[ i%nmodes ];
if ( mode === 'clamp' ) {
if ( j < 0 ) {
j = 0;
} else if ( j >= m ) {
j = m - 1;
}
} else if ( mode === 'wrap' ) {
if ( j < 0 ) {
j += m; // slight optimization to avoid modulo arithmetic when |j| <= m
if ( j < 0 ) {
j %= m;
if ( j !== 0 ) {
j += m;
}
}
} else if ( j >= m ) {
j -= m; // slight optimization to avoid modulo arithmetic when m < j <= 2m
if ( j >= m ) {
j %= m;
}
}
} else {
if ( mode === 'normalize' && j < 0 ) {
j += m;
}
if ( j < 0 || j >= m ) {
throw new RangeError( format( 'invalid argument. Subscripts must not exceed array dimensions. Subscript: `%u`. Value: `%d`.', i, j ) );
}
}
s = strides[ i ];
// Check if array view...
if ( s < 0 && offset === 0 ) {
idx -= j * s; // increments idx
} else {
idx += j * s; // may increment or decrement idx
}
}
return idx;
}
// EXPORTS //
module.exports = sub2ind;
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