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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 toUniqueNormalizedIndices = require( '@stdlib/ndarray/base/to-unique-normalized-indices' );
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' );
var join = require( '@stdlib/array/base/join' );
var format = require( '@stdlib/string/format' );
// MAIN //
/**
* Rotates an ndarray 90 degrees in a specified plane.
*
* ## Notes
*
* - If `k > 0`, the function rotates the plane from the first specified dimension toward the second specified dimension. This means that, for a two-dimensional ndarray and `dims = [0, 1]`, the function rotates the plane counterclockwise.
* - If `k < 0`, the function rotates the plane from the second specified dimension toward the first specified dimension. This means that, for a two-dimensional ndarray and `dims = [1, 0]`, the function rotates the plane clockwise.
* - Each provided dimension index must reside on the interval `[-ndims, ndims-1]`.
*
* @param {ndarray} x - input array
* @param {IntegerArray} dims - dimension indices defining the plane of rotation
* @param {integer} k - number of times to rotate by 90 degrees
* @param {boolean} writable - boolean indicating whether the returned ndarray should be writable
* @throws {RangeError} must provide exactly two dimension indices
* @throws {RangeError} input ndarray must have at least two dimensions
* @throws {RangeError} must provide valid dimension indices
* @throws {Error} must provide unique dimension indices
* @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 = rot90( x, [ 0, 1 ], 1, false );
* // returns <ndarray>[ [ 2, 4 ], [ 1, 3 ] ]
*/
function rot90( x, dims, k, writable ) {
var offset;
var sd0;
var sd1;
var sh;
var st;
var d0;
var d1;
var M;
var N;
var d;
if ( dims.length !== 2 ) {
throw new RangeError( format( 'invalid argument. Must provide exactly two dimension indices. Value: `[%s]`.', join( dims, ', ' ) ) );
}
sh = getShape( x, true );
if ( sh.length < 2 ) {
throw new RangeError( format( 'invalid argument. Input ndarray must have at least two dimensions. Number of dimensions: %d.', sh.length ) );
}
st = getStrides( x, true );
offset = getOffset( x );
// Resolve dimension indices...
d = toUniqueNormalizedIndices( dims, sh.length-1 );
if ( d === null ) {
throw new RangeError( format( 'invalid argument. Specified dimension index is out-of-bounds. Must be on the interval: [-%u, %u]. Value: `[%s]`.', sh.length, sh.length-1, join( dims, ', ' ) ) );
}
if ( d.length !== dims.length ) {
throw new Error( format( 'invalid argument. Must provide unique dimension indices. Value: `[%s]`.', join( dims, ', ' ) ) );
}
d0 = d[ 0 ];
d1 = d[ 1 ];
// Normalize `k` to the interval [0, 3]:
k %= 4;
if ( k < 0 ) {
k += 4;
}
// Cache the original shape and stride values for the rotation plane:
M = sh[ d0 ];
N = sh[ d1 ];
sd0 = st[ d0 ];
sd1 = st[ d1 ];
// Case: rotate 90 deg counterclockwise
if ( k === 1 ) {
sh[ d0 ] = N;
sh[ d1 ] = M;
st[ d0 ] = -sd1;
st[ d1 ] = sd0;
offset += ( N - 1 ) * sd1;
}
// Case: rotate 180 deg (i.e., reverse both dimensions in the rotation plane)
else if ( k === 2 ) {
st[ d0 ] = -sd0;
st[ d1 ] = -sd1;
offset += ( ( M - 1 ) * sd0 ) + ( ( N - 1 ) * sd1 );
}
// Case: rotate 270 deg counterclockwise (i.e., 90 deg clockwise)
else if ( k === 3 ) {
sh[ d0 ] = N;
sh[ d1 ] = M;
st[ d0 ] = sd1;
st[ d1 ] = -sd0;
offset += ( M - 1 ) * sd0;
}
return new x.constructor( getDType( x ), getData( x ), sh, st, offset, getOrder( x ), { // eslint-disable-line max-len
'readonly': !writable
});
}
// EXPORTS //
module.exports = rot90;
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