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* @license Apache-2.0
*
* Copyright (c) 2018 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 isPositiveInteger = require( '@stdlib/assert/is-positive-integer' ).isPrimitive;
var isnan = require( '@stdlib/math/base/assert/is-nan' );
var Float64Array = require( '@stdlib/array/float64' );
var format = require( '@stdlib/string/format' );
// MAIN //
/**
* Returns an accumulator function which incrementally computes a moving sum.
*
* @param {PositiveInteger} W - window size
* @throws {TypeError} must provide a positive integer
* @returns {Function} accumulator function
*
* @example
* var accumulator = incrmsum( 3 );
*
* var sum = accumulator();
* // returns null
*
* sum = accumulator( 2.0 );
* // returns 2.0
*
* sum = accumulator( -5.0 );
* // returns -3.0
*
* sum = accumulator( 3.0 );
* // returns 0.0
*
* sum = accumulator( 5.0 );
* // returns 3.0
*
* sum = accumulator();
* // returns 3.0
*/
function incrmsum( W ) {
var buf;
var sum;
var N;
var i;
if ( !isPositiveInteger( W ) ) {
throw new TypeError( format( 'invalid argument. Must provide a positive integer. Value: `%s`.', W ) );
}
buf = new Float64Array( W );
sum = 0.0;
i = -1;
N = 0;
return accumulator;
/**
* If provided a value, the accumulator function returns an updated sum. If not provided a value, the accumulator function returns the current sum.
*
* @private
* @param {number} [x] - input value
* @returns {(number|null)} sum or null
*/
function accumulator( x ) {
var k;
if ( arguments.length === 0 ) {
if ( N === 0 ) {
return null;
}
return sum;
}
// Update the index for managing the circular buffer:
i = (i+1) % W;
// Case: incoming value is NaN, the accumulated value is automatically NaN...
if ( isnan( x ) ) {
N = W; // explicitly set to avoid `N < W` branch
sum = NaN;
}
// Case: initial window...
else if ( N < W ) {
N += 1;
sum += x;
}
// Case: outgoing value is NaN, and, thus, we need to compute the accumulated value...
else if ( isnan( buf[ i ] ) ) {
N = 1;
sum = x;
for ( k = 0; k < W; k++ ) {
if ( k !== i ) {
if ( isnan( buf[ k ] ) ) {
N = W; // explicitly set to avoid `N < W` branch
sum = NaN;
break; // sum is automatically NaN, so no need to continue
}
N += 1;
sum += buf[ k ];
}
}
}
// Case: neither the current accumulated value nor the incoming value are NaN, so we need to update the accumulated value...
else if ( isnan( sum ) === false ) {
sum += x - buf[ i ];
}
// Case: the current accumulated value is NaN, so nothing to do until the buffer no longer contains NaN values...
buf[ i ] = x;
return sum;
}
}
// EXPORTS //
module.exports = incrmsum;
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