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const PINNED_IN_MEMORY = 0x7fffffffconst NOT_IN_LRU = 0x40000000export const EXPIRED_ENTRY = {	description: 'This cache entry value has been expired from the LRFU cache, and is waiting for garbage collection to be removed.'}/* bit pattern:*  < is-in-lru 1 bit > ...< mask/or bits 4 bits > <lru index 4 bits > < position in cache - 16 bits >*/export class LRFUExpirer {	constructor(options) {		this.lruSize = options && options.lruSize || 0x2000		this.reset()		startTimedCleanup(new WeakRef(this), options && options.cleanupInterval || 60000)	}	delete(entry) {		if (entry.position < NOT_IN_LRU) {			this.lru[(entry.position >> 16) & 15][entry.position & 0xffff] = null		}		entry.position |= NOT_IN_LRU	}	used(entry, expirationPriority) {		let originalPosition = entry.position		let orMask		if (expirationPriority < 0) {			// pin this in memory, first remove from LRFU and then mark it as pinned in memory			if (entry.position < NOT_IN_LRU) {				this.lru[(entry.position >> 16) & 15][entry.position & 0xffff] = null			}			entry.position = PINNED_IN_MEMORY			return		} else if (entry.position == PINNED_IN_MEMORY && expirationPriority == undefined) {			return		} else if (expirationPriority >= 0) {			let bits = 0			if (expirationPriority > (this.lruSize >> 2))				expirationPriority = this.lruSize >> 2			while (expirationPriority > 0) {				expirationPriority = expirationPriority >> 1				bits++			}			expirationPriority = bits		} else {			if (originalPosition >= 0)				expirationPriority = (originalPosition >> 20) & 15			else				expirationPriority = 0		}				let lruPosition		let lruIndex		if (originalPosition < NOT_IN_LRU) {			lruIndex = (originalPosition >> 16) & 15			if (lruIndex >= 3)				return // can't get any higher than this, don't do anything			let lru = this.lru[lruIndex]			// check to see if it is in the same generation			lruPosition = lru.position			if ((originalPosition > lruPosition ? lruPosition + this.lruSize : lruPosition) - originalPosition < (this.lruSize >> 3))				return // only recently added, don't promote			lru[originalPosition & 0xffff] = null // remove it, we are going to move/promote it			lruIndex++		} else			lruIndex = 0		this.insertEntry(entry, lruIndex, expirationPriority)	}	insertEntry(entry, lruIndex, expirationPriority) {		let lruPosition, nextLru = this.lru[lruIndex]		let orMask = 0xffff >> (16 - expirationPriority)		do {			// put it in the next lru			lruPosition = nextLru.position | orMask			let previousEntry = nextLru[lruPosition & 0xffff]			nextLru[lruPosition & 0xffff] = entry			if (entry)				entry.position = lruPosition | (expirationPriority << 20)			nextLru.position = ++lruPosition			if ((lruPosition & 0xffff) >= this.lruSize) {				// reset at the beginning of the lru cache				lruPosition &= 0x7fff0000				nextLru.position = lruPosition				nextLru.cycles++			}			entry = previousEntry			if (entry && (nextLru = this.lru[--lruIndex])) {				expirationPriority = ((entry.position || 0) >> 20) & 15				orMask = 0xffff >> (16 - expirationPriority)			} else				break		} while (true)		if (entry) {// this one was removed			entry.position |= NOT_IN_LRU			if (entry.cache)				entry.cache.onRemove(entry)			else if (entry.deref) // if we have already registered the entry in the finalization registry, just clear it				entry.value = EXPIRED_ENTRY		}	}	reset() {	/*	if (this.lru) {			for (let i = 0; i < 4; i++) {				for (let j = 0, l = this.lru.length; j < l; j++) {					let entry =	this.lru[i][j]					if (entry) {// this one was removed						entry.position |= NOT_IN_LRU						if (entry.cache)							entry.cache.onRemove(entry)						else if (entry.deref) // if we have already registered the entry in the finalization registry, just clear it							entry.value = EXPIRED_ENTRY					}				}			}		}*/		this.lru = []		for (let i = 0; i < 4; i++) {			this.lru[i] = new Array(this.lruSize)			this.lru[i].position = i << 16			this.lru[i].cycles = 0		}	}	cleanup() { // clean out a portion of the cache, so we can clean up over time if idle		let toClear = this.lruSize >> 4 // 1/16 of the lru cache at a time		for (let i = 3; i >= 0; i--) {			let lru = this.lru[i]			for (let j = 0, l = toClear; j < l; j++) {				if (lru[lru.position & 0xffff]) {					toClear--					this.insertEntry(null, i, 0)				} else {					if ((++lru.position & 0xffff) >= this.lruSize) {						// reset at the beginning of the lru cache						lru.position &= 0x7fff0000						lru.cycles++					}				}			}		}	}}function startTimedCleanup(reference, cleanupInterval) {	let interval = setInterval(() => {		let expirer = reference.deref()		if (expirer)			expirer.cleanup()		else			clearInterval(interval)	}, cleanupInterval)	if (interval.unref)		interval.unref()}