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) 2020 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 isNegativeZero = require( '@stdlib/math/base/assert/is-negative-zero' );
var isnan = require( '@stdlib/math/base/assert/is-nan' );
var GAPS = require( './gaps.json' );
// VARIABLES //
var NGAPS = GAPS.length;
// MAIN //
/**
* Sorts a double-precision floating-point strided array using Shellsort.
*
* ## Notes
*
* - This implementation uses the gap sequence proposed by Ciura (2001).
*
* ## References
*
* - Shell, Donald L. 1959. "A High-Speed Sorting Procedure." _Communications of the ACM_ 2 (7). Association for Computing Machinery: 30–32. doi:[10.1145/368370.368387](https://doi.org/10.1145/368370.368387).
* - Ciura, Marcin. 2001. "Best Increments for the Average Case of Shellsort." In _Fundamentals of Computation Theory_, 106–17. Springer Berlin Heidelberg. doi:[10.1007/3-540-44669-9\_12](https://doi.org/10.1007/3-540-44669-9_12).
*
* @param {PositiveInteger} N - number of indexed elements
* @param {number} order - sort order
* @param {Float64Array} x - input array
* @param {integer} strideX - stride length
* @param {NonNegativeInteger} offsetX - starting index
* @returns {Float64Array} input array
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var x = new Float64Array( [ 1.0, -2.0, 3.0, -4.0 ] );
*
* dsortsh( x.length, 1.0, x, 1, 0 );
* // x => <Float64Array>[ -4.0, -2.0, 1.0, 3.0 ]
*/
function dsortsh( N, order, x, strideX, offsetX ) {
var flg;
var gap;
var v;
var u;
var i;
var j;
var k;
if ( N <= 0 || order === 0.0 ) {
return x;
}
// For a positive stride, sorting in decreasing order is equivalent to providing a negative stride and sorting in increasing order, and, for a negative stride, sorting in decreasing order is equivalent to providing a positive stride and sorting in increasing order...
if ( order < 0.0 ) {
strideX *= -1;
offsetX -= (N-1) * strideX;
}
for ( i = 0; i < NGAPS; i++ ) {
gap = GAPS[ i ];
for ( j = gap; j < N; j++ ) {
v = x[ offsetX+(j*strideX) ];
// If `NaN`, the current value is already sorted to its place...
if ( isnan( v ) ) {
continue;
}
// Perform insertion sort on the "gapped" subarray...
flg = isNegativeZero( v );
for ( k = j; k >= gap; k -= gap ) {
u = x[ offsetX+((k-gap)*strideX) ];
if ( u <= v && !(flg && u === v) ) {
break;
}
x[ offsetX+(k*strideX) ] = u;
}
x[ offsetX+(k*strideX) ] = v;
}
}
return x;
}
// EXPORTS //
module.exports = dsortsh;
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