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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 f32 = require( '@stdlib/number/float64/base/to-float32' );
var isnanf = require( '@stdlib/math/base/assert/is-nanf' );
var absf = require( '@stdlib/math/base/special/absf' );
// MAIN //
/**
* Computes the sum of single-precision floating-point strided array elements, ignoring `NaN` values, using an improved Kahan–Babuška algorithm and alternative indexing semantics, and returning the number of non-`NaN` elements.
*
* ## Method
*
* - This implementation uses an "improved Kahan–Babuška algorithm", as described by Neumaier (1974).
*
* ## References
*
* - Neumaier, Arnold. 1974. "Rounding Error Analysis of Some Methods for Summing Finite Sums." _Zeitschrift Für Angewandte Mathematik Und Mechanik_ 54 (1): 39–51. doi:[10.1002/zamm.19740540106](https://doi.org/10.1002/zamm.19740540106).
*
* @param {PositiveInteger} N - number of indexed elements
* @param {Float32Array} x - input array
* @param {integer} strideX - stride length for `x`
* @param {NonNegativeInteger} offsetX - starting index for `x`
* @param {Float32Array} sum - output array for storing the sum
* @param {NonNegativeInteger} offsetSum - starting index for `sum`
* @param {Int64Array} count - output array for storing the number of non-NaN elements
* @param {NonNegativeInteger} offsetCount - starting index for `count`
* @returns {Float32Array} `sum`
*
* @example
* var Float32Array = require( '@stdlib/array/float32' );
* var Int64Array = require( '@stdlib/array/int64' );
*
* var x = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0, NaN, NaN ] );
* var sum = new Float32Array( 1 );
* var count = new Int64Array( 1 );
*
* var v = snannsumkbn( 5, x, 2, 1, sum, 0, count, 0 );
* // returns <Float32Array>[ 5.0 ]
*
* var n = count.get( 0 );
* // returns <Int64>[ 4n ]
*/
function snannsumkbn( N, x, strideX, offsetX, sum, offsetSum, count, offsetCount ) { // eslint-disable-line max-len
var flg;
var ix;
var s;
var v;
var t;
var c;
var n;
var i;
if ( N <= 0 ) {
sum[ offsetSum ] = 0.0;
count.set( 0, offsetCount );
return sum;
}
ix = offsetX;
if ( strideX === 0 ) {
if ( isnanf( x[ ix ] ) ) {
sum[ offsetSum ] = 0.0;
count.set( 0, offsetCount );
return sum;
}
sum[ offsetSum ] = f32( x[ ix ] * N );
count.set( N, offsetCount );
return sum;
}
// Find the first non-NaN element...
for ( i = 0; i < N; i++ ) {
v = x[ ix ];
if ( isnanf( v ) === false ) {
break;
}
ix += strideX;
}
if ( i === N ) {
sum[ offsetSum ] = 0.0;
count.set( 0, offsetCount );
return sum;
}
n = 1;
s = v;
ix += strideX;
i += 1;
// In order to preserve the sign of zero which can be lost during compensated summation below, find the first non-zero element...
if ( s === 0.0 ) {
for ( ; i < N; i++ ) {
v = x[ ix ];
if ( isnanf( v ) === false ) {
if ( v !== 0.0 ) {
flg = true;
break;
}
s = f32( s + v );
n += 1;
}
ix += strideX;
}
} else {
flg = true;
}
c = 0.0;
for ( ; i < N; i++ ) {
v = x[ ix ];
if ( isnanf( v ) === false ) {
t = f32( s + v );
if ( absf( s ) >= absf( v ) ) {
c = f32( c + f32( f32( s-t ) + v ) );
} else {
c = f32( c + f32( f32( v-t ) + s ) );
}
s = t;
n += 1;
}
ix += strideX;
}
sum[ offsetSum ] = ( flg ) ? f32( s+c ) : s;
count.set( n, offsetCount );
return sum;
}
// EXPORTS //
module.exports = snannsumkbn;
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