/**
* @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.
*/

#include "stdlib/stats/base/smeankbn.h"
#include "stdlib/blas/ext/base/ssum.h"
#include <stdint.h>

/**
* Computes the arithmetic mean of a single-precision floating-point strided array using an improved Kahan–Babuška algorithm.
*
* ## 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 N       number of indexed elements
* @param X       input array
* @param stride  stride length
* @return        output value
*/
float stdlib_strided_smeankbn( const int64_t N, const float *X, const int64_t stride ) {
	if ( N <= 0 ) {
		return 0.0 / 0.0; // NaN
	}
	if ( N == 1 || stride == 0 ) {
		return X[ 0 ];
	}
	return (double)stdlib_strided_ssum( N, X, stride ) / (double)N;
}