107 lines
3.4 KiB
C
107 lines
3.4 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 "stdlib/ndarray/base/vind2bind.h"
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#include "stdlib/ndarray/index_modes.h"
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#include "stdlib/ndarray/orders.h"
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#include <stdint.h>
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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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* ## Notes
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*
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* - In "error" mode, the function returns `-1` if an index is out-of-bounds.
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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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* @param offset location of the first indexed value **based** on the stride array
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* @param order specifies whether an array is row-major (C-style) or column-major (Fortran-style)
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* @param idx linear index in an array view
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* @param mode specifies how to handle a linear index which exceeds array dimensions
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* @return index
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*
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* @example
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* #include "stdlib/ndarray/base/vind2bind.h"
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* #include "stdlib/ndarray/index_modes.h"
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* #include "stdlib/ndarray/orders.h"
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*
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* int64_t ndims = 2;
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* int64_t shape[] = { 3, 3 };
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* int64_t strides[] = { -3, 1 };
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* int64_t offset = 6;
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*
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* int64_t idx = stdlib_ndarray_vind2bind( ndims, shape, strides, offset, STDLIB_NDARRAY_ROW_MAJOR, 1, STDLIB_NDARRAY_INDEX_ERROR );
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* // returns 7
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*/
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int64_t stdlib_ndarray_vind2bind( int64_t ndims, int64_t *shape, int64_t *strides, int64_t offset, enum STDLIB_NDARRAY_ORDER order, int64_t idx, enum STDLIB_NDARRAY_INDEX_MODE mode ) {
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int64_t len;
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int64_t ind;
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int64_t s;
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int64_t i;
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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 == STDLIB_NDARRAY_INDEX_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 == STDLIB_NDARRAY_INDEX_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*( (int64_t)( idx/len ) ); // this is equivalent to `idx mod len`, where the result has same sign as dividend (i.e., `idx`); cannot use `%` as the sign of the result is implementation defined in C
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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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return -1;
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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 == STDLIB_NDARRAY_COLUMN_MAJOR ) {
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for ( i = 0; i < ndims; i++ ) {
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s = idx % shape[ i ]; // assume nonnegative "shape"
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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 ]; // assume nonnegative "shape"
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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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