110 lines
3.1 KiB
JavaScript
110 lines
3.1 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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// MAIN //
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/**
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* Converts a linear index in an array view to a linear index in an underlying data buffer.
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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 in an array view
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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 {NonNegativeInteger} linear index in an underlying data buffer
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*
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* @example
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* var shape = [ 3, 3 ];
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* var strides = [ -3, 1 ];
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* var offset = 6;
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* var order = 'row-major';
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* var mode = 'throw';
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*
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* var ind = vind2bind( shape, strides, offset, order, 1, mode );
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* // returns 7
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*/
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function vind2bind( shape, strides, offset, order, idx, mode ) {
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var ndims;
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var len;
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var ind;
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var s;
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var i;
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ndims = shape.length;
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len = 1;
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for ( i = 0; i < ndims; i++ ) {
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len *= shape[ i ];
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}
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if ( mode === 'clamp' ) {
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if ( idx < 0 ) {
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idx = 0;
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} else if ( idx >= len ) {
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idx = len - 1;
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}
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} else if ( mode === 'wrap' ) {
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if ( idx < 0 ) {
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idx += len; // slight optimization to avoid modulo arithmetic when |idx| <= len
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if ( idx < 0 ) {
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idx %= len;
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if ( idx !== 0 ) {
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idx += len;
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}
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}
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} else if ( idx >= len ) {
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idx -= len; // slight optimization to avoid modulo arithmetic when len < idx <= 2*len
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if ( idx >= len ) {
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idx %= len;
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}
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}
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} else if ( idx < 0 || idx >= len ) {
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throw new RangeError( 'invalid argument. Linear index must not exceed array dimensions. Number of array elements: ' + len + '. Value: `' + idx + '`.' );
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}
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// Trivial case where the offset into the underlying data buffer is 0...
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if ( offset === 0 ) {
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return idx;
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}
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// The approach which follows is to resolve a view index to its subscripts and then plug the subscripts into the standard formula for computing the linear index in the underlying data buffer...
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ind = offset;
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if ( order === 'column-major' ) {
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for ( i = 0; i < ndims; i++ ) {
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s = idx % shape[ i ];
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idx -= s;
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idx /= shape[ i ];
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ind += s * strides[ i ];
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}
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return ind;
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}
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// Case: row-major
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for ( i = ndims-1; i >= 0; i-- ) {
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s = idx % shape[ i ];
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idx -= s;
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idx /= shape[ i ];
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ind += s * strides[ i ];
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}
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return ind;
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}
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// EXPORTS //
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module.exports = vind2bind;
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