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 float64ToFloat32 = require( '@stdlib/number/float64/base/to-float32' );
  var floor = require( '@stdlib/math/base/special/floor' );
  
  
  // VARIABLES //
  
  // Blocksize for pairwise summation (NOTE: decreasing the blocksize decreases rounding error as more pairs are summed, but also decreases performance. Because the inner loop is unrolled eight times, the blocksize is effectively `16`.):
  var BLOCKSIZE = 128;
  
  
  // MAIN //
  
  /**
  * Adds a constant to each single-precision floating-point strided array element and computes the sum using pairwise summation with extended accumulation.
  *
  * ## 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 {number} alpha - constant
  * @param {Float32Array} x - input array
  * @param {integer} stride - stride length
  * @param {NonNegativeInteger} offset - starting index
  * @returns {number} sum
  *
  * @example
  * var Float32Array = require( '@stdlib/array/float32' );
  * var floor = require( '@stdlib/math/base/special/floor' );
  *
  * var x = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
  * var N = floor( x.length / 2 );
  *
  * var v = sdsapxsumpw( N, 5.0, x, 2, 1 );
  * // returns 25.0
  */
  function sdsapxsumpw( N, alpha, x, stride, offset ) {
  	var ix;
  	var s0;
  	var s1;
  	var s2;
  	var s3;
  	var s4;
  	var s5;
  	var s6;
  	var s7;
  	var M;
  	var s;
  	var n;
  	var i;
  
  	if ( N <= 0 ) {
  		return 0.0;
  	}
  	if ( N === 1 || stride === 0 ) {
  		return float64ToFloat32( alpha + x[ offset ] );
  	}
  	ix = offset;
  	if ( N < 8 ) {
  		// Use simple summation...
  		s = 0.0;
  		for ( i = 0; i < N; i++ ) {
  			s += alpha + x[ ix ];
  			ix += stride;
  		}
  		return float64ToFloat32( s );
  	}
  	if ( N <= BLOCKSIZE ) {
  		// Sum a block with 8 accumulators (by loop unrolling, we lower the effective blocksize to 16)...
  		s0 = alpha + x[ ix ];
  		s1 = alpha + x[ ix+stride ];
  		s2 = alpha + x[ ix+(2*stride) ];
  		s3 = alpha + x[ ix+(3*stride) ];
  		s4 = alpha + x[ ix+(4*stride) ];
  		s5 = alpha + x[ ix+(5*stride) ];
  		s6 = alpha + x[ ix+(6*stride) ];
  		s7 = alpha + x[ ix+(7*stride) ];
  		ix += 8 * stride;
  
  		M = N % 8;
  		for ( i = 8; i < N-M; i += 8 ) {
  			s0 += alpha + x[ ix ];
  			s1 += alpha + x[ ix+stride ];
  			s2 += alpha + x[ ix+(2*stride) ];
  			s3 += alpha + x[ ix+(3*stride) ];
  			s4 += alpha + x[ ix+(4*stride) ];
  			s5 += alpha + x[ ix+(5*stride) ];
  			s6 += alpha + x[ ix+(6*stride) ];
  			s7 += alpha + x[ ix+(7*stride) ];
  			ix += 8 * stride;
  		}
  		// Pairwise sum the accumulators:
  		s = ((s0+s1) + (s2+s3)) + ((s4+s5) + (s6+s7));
  
  		// Clean-up loop...
  		for ( i; i < N; i++ ) {
  			s += alpha + x[ ix ];
  			ix += stride;
  		}
  		return float64ToFloat32( s );
  	}
  	// Recurse by dividing by two, but avoiding non-multiples of unroll factor...
  	n = floor( N/2 );
  	n -= n % 8;
  	return float64ToFloat32( sdsapxsumpw( n, alpha, x, stride, ix ) + sdsapxsumpw( N-n, alpha, x, stride, ix+(n*stride) ) ); // eslint-disable-line max-len
  }
  
  
  // EXPORTS //
  
  module.exports = sdsapxsumpw;
  