53 lines
1.6 KiB
C
53 lines
1.6 KiB
C
/**
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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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#include <stdint.h>
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#include "stdlib/ndarray/base/strides2offset.h"
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/**
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* Returns the index offset which specifies the location of the first indexed value in a multidimensional array based on a stride array.
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*
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* @param ndims number of dimensions
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* @param shape array shape (dimensions)
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* @param strides array strides
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* @return offset
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*
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* @example
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* #include "stdlib/ndarray/base/strides2offset.h"
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*
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* int64_t ndims = 3;
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* int64_t shape[] = { 2, 3, 10 };
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* int64_t strides[] = { 30, -10, 1 };
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*
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* int64_t offset = stdlib_ndarray_strides2offset( ndims, shape, strides );
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* // returns 20
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*/
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int64_t stdlib_ndarray_strides2offset( int64_t ndims, int64_t *shape, int64_t *strides ) {
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int64_t offset;
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int64_t i;
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offset = 0;
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for ( i = 0; i < ndims; i++ ) {
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if ( strides[ i ] < 0 ) {
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// Note that, since the stride is negative, this operation increments, not decrements, the offset...
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offset -= strides[ i ] * ( shape[ i ]-1 );
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}
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}
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return offset;
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}
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