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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 isNegativeZero = require( '@stdlib/math/base/assert/is-negative-zero' );
var PINF = require( '@stdlib/constants/float64/pinf' );
var Float64Array = require( '@stdlib/array/float64' );
var format = require( '@stdlib/string/format' );
// MAIN //
/**
* Returns an accumulator function which incrementally computes a moving minimum value.
*
* @param {PositiveInteger} W - window size
* @throws {TypeError} must provide a positive integer
* @returns {Function} accumulator function
*
* @example
* var accumulator = incrmmin( 3 );
*
* var m = accumulator();
* // returns null
*
* m = accumulator( 2.0 );
* // returns 2.0
*
* m = accumulator( -5.0 );
* // returns -5.0
*
* m = accumulator( 3.0 );
* // returns -5.0
*
* m = accumulator( 5.0 );
* // returns -5.0
*
* m = accumulator();
* // returns -5.0
*/
function incrmmin( W ) {
var buf;
var min;
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 );
min = PINF;
i = -1;
N = 0;
return accumulator;
/**
* If provided a value, the accumulator function returns an updated minimum. If not provided a value, the accumulator function returns the current minimum.
*
* @private
* @param {number} [x] - input value
* @returns {(number|null)} minimum value or null
*/
function accumulator( x ) {
var v;
var k;
if ( arguments.length === 0 ) {
if ( N === 0 ) {
return null;
}
return min;
}
// Update the index for managing the circular buffer:
i = (i+1) % W;
// Case: update initial window...
if ( N < W ) {
N += 1;
if (
isnan( x ) ||
x < min ||
( x === min && isNegativeZero( x ) )
) {
min = x;
}
}
// Case: incoming value is NaN or less than current minimum value...
else if ( isnan( x ) || x < min ) {
min = x;
}
// Case: outgoing value is the current minimum and the new value is greater than the minimum, and, thus, we need to find a new minimum among the current values...
else if ( ( buf[ i ] === min && x > min ) || isnan( buf[ i ] ) ) {
min = x;
for ( k = 0; k < W; k++ ) {
if ( k !== i ) {
v = buf[ k ];
if ( isnan( v ) ) {
min = v;
break; // no need to continue searching
}
if ( v < min || ( v === min && isNegativeZero( v ) ) ) {
min = v;
}
}
}
}
// Case: outgoing value is the current minimum, which is zero, and the new value is also zero, and, thus, we need to correctly handle signed zeros...
else if ( buf[ i ] === min && x === min && x === 0.0 ) {
if ( isNegativeZero( x ) ) {
min = x;
} else if ( isNegativeZero( buf[ i ] ) ) {
// Because the outgoing and incoming are different signs (-,+), we need to search the buffer to see if it contains a negative zero. If so, the minimum value remains negative zero; otherwise, the minimum value is incoming value...
min = x;
for ( k = 0; k < W; k++ ) {
if ( k !== i && isNegativeZero( buf[ k ] ) ) {
min = buf[ k ];
break;
}
}
}
// Case: the outgoing and incoming values are both positive zero, so nothing changes
}
// Case: updating existing window; however, the minimum value does not change so nothing to do but update our buffer...
buf[ i ] = x;
return min;
}
}
// EXPORTS //
module.exports = incrmmin;
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