Press n or j to go to the next uncovered block, b, p or k for the previous block.
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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 floor = require( '@stdlib/math/base/special/floor' );
// MAIN //
/**
* Circularly shifts the elements of a strided array by a specified number of positions.
*
* ## Notes
*
* - This implementation is based on the "trinity rotation" (a.k.a., conjoined triple reversal) algorithm introduced in <https://github.com/scandum/rotate/tree/6d0d2d56d10454def027e35921890200b45fe82c>, by Igor van den Hoven.
*
* @private
* @param {PositiveInteger} N - number of indexed elements
* @param {integer} k - number of positions to shift
* @param {Object} x - input array object
* @param {Collection} x.data - input array data
* @param {Array<Function>} x.accessors - array element accessors
* @param {integer} strideX - stride length
* @param {NonNegativeInteger} offsetX - starting index
* @returns {Object} input array object
*/
function gcircshift( N, k, x, strideX, offsetX ) {
var right;
var left;
var xbuf;
var tmp;
var set;
var get;
var pa;
var pb;
var pc;
var pd;
var n;
var s;
var i;
// Cache reference to array data:
xbuf = x.data;
// Cache a reference to the element accessors:
get = x.accessors[ 0 ];
set = x.accessors[ 1 ];
s = strideX;
// For a right circular shift by `k`, the left partition has `N-k` elements...
left = N - k;
right = k;
if ( left < right ) {
pa = offsetX;
pb = pa + ( left * s );
pc = pb;
pd = pb + ( right * s );
// Four-way swap from both ends and the split point...
n = floor( left / 2 );
for ( i = 0; i < n; i++ ) {
pb -= s;
pd -= s;
tmp = get( xbuf, pb );
set( xbuf, pb, get( xbuf, pa ) );
set( xbuf, pa, get( xbuf, pc ) );
set( xbuf, pc, get( xbuf, pd ) );
set( xbuf, pd, tmp );
pa += s;
pc += s;
}
// Three-way rotation for the remaining bridge...
n = floor( ( ( pd - pc ) / s ) / 2 );
for ( i = 0; i < n; i++ ) {
pd -= s;
tmp = get( xbuf, pc );
set( xbuf, pc, get( xbuf, pd ) );
set( xbuf, pd, get( xbuf, pa ) );
set( xbuf, pa, tmp );
pa += s;
pc += s;
}
// Standard reversal of any remaining elements...
n = floor( ( ( pd - pa ) / s ) / 2 );
for ( i = 0; i < n; i++ ) {
pd -= s;
tmp = get( xbuf, pa );
set( xbuf, pa, get( xbuf, pd ) );
set( xbuf, pd, tmp );
pa += s;
}
} else if ( left > right ) {
pa = offsetX;
pb = pa + ( left * s );
pc = pb;
pd = pb + ( right * s );
// Four-way swap from both ends and the split point...
n = floor( right / 2 );
for ( i = 0; i < n; i++ ) {
pb -= s;
pd -= s;
tmp = get( xbuf, pb );
set( xbuf, pb, get( xbuf, pa ) );
set( xbuf, pa, get( xbuf, pc ) );
set( xbuf, pc, get( xbuf, pd ) );
set( xbuf, pd, tmp );
pa += s;
pc += s;
}
// Three-way rotation for the remaining bridge...
n = floor( ( ( pb - pa ) / s ) / 2 );
for ( i = 0; i < n; i++ ) {
pb -= s;
pd -= s;
tmp = get( xbuf, pb );
set( xbuf, pb, get( xbuf, pa ) );
set( xbuf, pa, get( xbuf, pd ) );
set( xbuf, pd, tmp );
pa += s;
}
// Standard reversal of any remaining elements...
n = floor( ( ( pd - pa ) / s ) / 2 );
for ( i = 0; i < n; i++ ) {
pd -= s;
tmp = get( xbuf, pa );
set( xbuf, pa, get( xbuf, pd ) );
set( xbuf, pd, tmp );
pa += s;
}
} else {
// Simple pairwise swap...
pa = offsetX;
pb = pa + ( left * s );
for ( i = 0; i < left; i++ ) {
tmp = get( xbuf, pa );
set( xbuf, pa, get( xbuf, pb ) );
set( xbuf, pb, tmp );
pa += s;
pb += s;
}
}
return x;
}
// EXPORTS //
module.exports = gcircshift;
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