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* @license Apache-2.0
*
* Copyright (c) 2026 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var getDType = require( '@stdlib/ndarray/base/dtype' );
var getShape = require( '@stdlib/ndarray/base/shape' );
var getStrides = require( '@stdlib/ndarray/base/strides' );
var getOffset = require( '@stdlib/ndarray/base/offset' );
var getOrder = require( '@stdlib/ndarray/base/order' );
var getData = require( '@stdlib/ndarray/base/data-buffer' );
// MAIN //
/**
* Rotates a matrix (or a stack of matrices) 90 degrees clockwise.
*
* @param {ndarray} x - input array
* @param {integer} k - number of times to rotate by 90 degrees
* @param {boolean} writable - boolean indicating whether the returned ndarray should be writable
* @returns {ndarray} ndarray view
*
* @example
* var array = require( '@stdlib/ndarray/array' );
*
* var x = array( [ [ 1, 2 ], [ 3, 4 ] ] );
* // returns <ndarray>[ [ 1, 2 ], [ 3, 4 ] ]
*
* var y = rotr90( x, 1, false );
* // returns <ndarray>[ [ 3, 1 ], [ 4, 2 ] ]
*
*/
function rotr90( x, k, writable ) {
var offset;
var sh;
var st;
var sm;
var sn;
var M;
var N;
var d;
sh = getShape( x, true );
d = sh.length;
if ( d < 2 ) {
return x;
}
st = getStrides( x, true );
offset = getOffset( x );
// Normalize k to the range [0, 3]:
k %= 4;
if ( k < 0 ) {
k += 4;
}
// Cache the original shape and stride values for the last two dimensions:
M = sh[ d-2 ];
N = sh[ d-1 ];
sm = st[ d-2 ];
sn = st[ d-1 ];
if ( k === 1 ) {
sh[ d-2 ] = N;
sh[ d-1 ] = M;
st[ d-2 ] = sn;
st[ d-1 ] = -sm;
offset += ( M - 1 ) * sm;
} else if ( k === 2 ) {
st[ d-2 ] = -sm;
st[ d-1 ] = -sn;
offset += ( ( M - 1 ) * sm ) + ( ( N - 1 ) * sn );
} else if ( k === 3 ) {
sh[ d-2 ] = N;
sh[ d-1 ] = M;
st[ d-2 ] = -sn;
st[ d-1 ] = sm;
offset += ( N - 1 ) * sn;
}
return new x.constructor( getDType( x ), getData( x ), sh, st, offset, getOrder( x ), { // eslint-disable-line max-len
'readonly': !writable
});
}
// EXPORTS //
module.exports = rotr90;
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