main.c (1592B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2018 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 #include <stdint.h> 20 #include "stdlib/ndarray/base/strides2offset.h" 21 22 /** 23 * Returns the index offset which specifies the location of the first indexed value in a multidimensional array based on a stride array. 24 * 25 * @param ndims number of dimensions 26 * @param shape array shape (dimensions) 27 * @param strides array strides 28 * @return offset 29 * 30 * @example 31 * #include "stdlib/ndarray/base/strides2offset.h" 32 * 33 * int64_t ndims = 3; 34 * int64_t shape[] = { 2, 3, 10 }; 35 * int64_t strides[] = { 30, -10, 1 }; 36 * 37 * int64_t offset = stdlib_ndarray_strides2offset( ndims, shape, strides ); 38 * // returns 20 39 */ 40 int64_t stdlib_ndarray_strides2offset( int64_t ndims, int64_t *shape, int64_t *strides ) { 41 int64_t offset; 42 int64_t i; 43 44 offset = 0; 45 for ( i = 0; i < ndims; i++ ) { 46 if ( strides[ i ] < 0 ) { 47 // Note that, since the stride is negative, this operation increments, not decrements, the offset... 48 offset -= strides[ i ] * ( shape[ i ]-1 ); 49 } 50 } 51 return offset; 52 }