152 lines
4.0 KiB
JavaScript
152 lines
4.0 KiB
JavaScript
/**
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* @license Apache-2.0
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*
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* Copyright (c) 2018 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var isPositiveInteger = require( '@stdlib/assert/is-positive-integer' ).isPrimitive;
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var isnan = require( '@stdlib/math/base/assert/is-nan' );
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var isPositiveZero = require( '@stdlib/math/base/assert/is-positive-zero' );
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var NINF = require( '@stdlib/constants/float64/ninf' );
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var Float64Array = require( '@stdlib/array/float64' );
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// MAIN //
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/**
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* Returns an accumulator function which incrementally computes a moving maximum value.
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*
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* @param {PositiveInteger} W - window size
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* @throws {TypeError} must provide a positive integer
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* @returns {Function} accumulator function
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*
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* @example
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* var accumulator = incrmmax( 3 );
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*
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* var m = accumulator();
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* // returns null
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*
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* m = accumulator( 2.0 );
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* // returns 2.0
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*
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* m = accumulator( -5.0 );
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* // returns 2.0
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*
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* m = accumulator( 3.0 );
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* // returns 3.0
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*
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* m = accumulator( 5.0 );
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* // returns 5.0
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*
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* m = accumulator();
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* // returns 5.0
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*/
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function incrmmax( W ) {
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var buf;
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var max;
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var N;
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var i;
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if ( !isPositiveInteger( W ) ) {
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throw new TypeError( 'invalid argument. Must provide a positive integer. Value: `' + W + '`.' );
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}
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buf = new Float64Array( W );
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max = NINF;
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i = -1;
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N = 0;
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return accumulator;
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/**
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* If provided a value, the accumulator function returns an updated maximum. If not provided a value, the accumulator function returns the current maximum.
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*
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* @private
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* @param {number} [x] - input value
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* @returns {(number|null)} maximum value or null
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*/
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function accumulator( x ) {
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var v;
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var k;
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if ( arguments.length === 0 ) {
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if ( N === 0 ) {
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return null;
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}
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return max;
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}
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// Update the index for managing the circular buffer:
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i = (i+1) % W;
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// Case: update initial window...
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if ( N < W ) {
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N += 1;
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if (
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isnan( x ) ||
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x > max ||
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( x === max && isPositiveZero( x ) )
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) {
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max = x;
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}
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}
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// Case: incoming value is NaN or greater than current maximum value...
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else if ( isnan( x ) || x > max ) {
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max = x;
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}
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// Case: outgoing value is the current maximum and the new value is less than the maximum, and, thus, we need to find a new maximum among the current values...
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else if ( ( buf[ i ] === max && x < max ) || isnan( buf[ i ] ) ) {
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max = x;
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for ( k = 0; k < W; k++ ) {
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if ( k !== i ) {
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v = buf[ k ];
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if ( isnan( v ) ) {
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max = v;
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break; // no need to continue searching
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}
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if ( v > max || ( v === max && isPositiveZero( v ) ) ) {
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max = v;
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}
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}
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}
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}
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// Case: outgoing value is the current maximum, which is zero, and the new value is also zero, and, thus, we need to correctly handle signed zeros...
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else if ( buf[ i ] === max && x === max && x === 0.0 ) {
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if ( isPositiveZero( x ) ) {
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max = x;
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} else if ( isPositiveZero( buf[ i ] ) ) {
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// Because the outgoing and incoming are different signs (+,-), we need to search the buffer to see if it contains a positive zero. If so, the maximum value remains positive zero; otherwise, the maximum value is incoming value...
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max = x;
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for ( k = 0; k < W; k++ ) {
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if ( k !== i && isPositiveZero( buf[ k ] ) ) {
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max = buf[ k ];
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break;
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}
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}
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}
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// Case: the outgoing and incoming values are both negative zero, so nothing changes
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}
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// Case: updating existing window; however, the maximum value does not change so nothing to do but update our buffer...
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buf[ i ] = x;
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return max;
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}
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}
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// EXPORTS //
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module.exports = incrmmax;
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