56 lines
1.7 KiB
C
56 lines
1.7 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/wrap_index.h"
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/**
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* Wraps an index on the interval `[0,max]`.
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*
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* @param idx index
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* @param max maximum index (should be nonnegative)
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* @return index
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*
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* @example
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* #include "stdlib/ndarray/base/wrap_index.h"
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*
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* int64_t idx = stdlib_ndarray_wrap_index( 13, 10 );
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* // returns 2
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*/
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int64_t stdlib_ndarray_wrap_index( int64_t idx, int64_t max ) {
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int64_t mp1 = max + 1; // WARNING: possibility of overflow (although, in practice, `max` should never be that large)
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if ( idx < 0 ) {
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idx += mp1; // slight optimization to avoid modulo arithmetic when |idx| <= max+1
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if ( idx < 0 ) {
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idx -= mp1*( (int64_t)( idx/mp1 ) ); // this is equivalent to `idx mod mp1`, 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 += mp1;
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}
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}
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return idx;
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}
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if ( idx > max ) {
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idx -= mp1; // slight optimization to avoid modulo arithmetic when max+1 < idx <= 2*(max+1)
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if ( idx > max ) {
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idx %= mp1;
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}
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return idx;
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}
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return idx;
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}
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