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 floor = require( '@stdlib/math/base/special/floor' );
// VARIABLES //
var M = 3;
// MAIN //
/**
* Reverses a double-precision floating-point strided array in-place.
*
* @param {PositiveInteger} N - number of indexed elements
* @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, 5.0, -6.0 ] );
*
* drev( 3, x, 1, x.length-3 );
* // x => <Float64Array>[ 1.0, -2.0, 3.0, -6.0, 5.0, -4.0 ]
*/
function drev( N, x, strideX, offsetX ) {
var tmp;
var ix;
var iy;
var m;
var n;
var i;
if ( N <= 0 ) {
return x;
}
n = floor( N/2 );
ix = offsetX;
// Use loop unrolling if the stride is equal to `1`...
if ( strideX === 1 ) {
m = n % M;
iy = ix + N - 1;
// If we have a remainder, run a clean-up loop...
if ( m > 0 ) {
for ( i = 0; i < m; i++ ) {
tmp = x[ ix ];
x[ ix ] = x[ iy ];
x[ iy ] = tmp;
ix += strideX;
iy -= strideX;
}
}
if ( n < M ) {
return x;
}
for ( i = m; i < n; i += M ) {
tmp = x[ ix ];
x[ ix ] = x[ iy ];
x[ iy ] = tmp;
tmp = x[ ix+1 ];
x[ ix+1 ] = x[ iy-1 ];
x[ iy-1 ] = tmp;
tmp = x[ ix+2 ];
x[ ix+2 ] = x[ iy-2 ];
x[ iy-2 ] = tmp;
ix += M;
iy -= M;
}
return x;
}
iy = ix + ( (N-1) * strideX );
for ( i = 0; i < n; i++ ) {
tmp = x[ ix ];
x[ ix ] = x[ iy ];
x[ iy ] = tmp;
ix += strideX;
iy -= strideX;
}
return x;
}
// EXPORTS //
module.exports = drev;
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