text: /**
  * @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 isnan = require( '@stdlib/math-base-assert-is-nan' );
  var sum = require( './ndarray.js' );
  
  
  // MAIN //
  
  /**
  * Computes the sum of double-precision floating-point strided array elements, ignoring `NaN` values and using pairwise summation.
  *
  * ## Method
  *
  * -   This implementation uses pairwise summation, which accrues rounding error `O(log2 N)` instead of `O(N)`. The recursion depth is also `O(log2 N)`.
  *
  * ## References
  *
  * -   Higham, Nicholas J. 1993. "The Accuracy of Floating Point Summation." _SIAM Journal on Scientific Computing_ 14 (4): 783–99. doi:[10.1137/0914050](https://doi.org/10.1137/0914050).
  *
  * @param {PositiveInteger} N - number of indexed elements
  * @param {Float64Array} x - input array
  * @param {integer} stride - stride length
  * @returns {number} sum
  *
  * @example
  * var Float64Array = require( '@stdlib/array-float64' );
  *
  * var x = new Float64Array( [ 1.0, -2.0, NaN, 2.0 ] );
  * var N = x.length;
  *
  * var v = dnansumpw( N, x, 1 );
  * // returns 1.0
  */
  function dnansumpw( N, x, stride ) {
  	var ix;
  	var s;
  	var i;
  
  	if ( N <= 0 ) {
  		return 0.0;
  	}
  	if ( N === 1 || stride === 0 ) {
  		if ( isnan( x[ 0 ] ) ) {
  			return 0.0;
  		}
  		return x[ 0 ];
  	}
  	if ( stride < 0 ) {
  		ix = (1-N) * stride;
  	} else {
  		ix = 0;
  	}
  	if ( N < 8 ) {
  		// Use simple summation...
  		s = 0.0;
  		for ( i = 0; i < N; i++ ) {
  			if ( isnan( x[ ix ] ) === false ) {
  				s += x[ ix ];
  			}
  			ix += stride;
  		}
  		return s;
  	}
  	return sum( N, x, stride, ix );
  }
  
  
  // EXPORTS //
  
  module.exports = dnansumpw;
  