different performance

setbit_performance

/*
Different performance for https://github.com/ceejbot/xx-bloom/blob/master/lib/bloom.js
Output (2.4 GHz Intel Core i7):
setbit cost: 24304ms
fastSetbit cost: 1ms
*/

var assert = require('assert')

function setbit(bit){
	var pos = 0
	var shift = bit
	while (shift > 7){
		pos++
		shift -= 8
	}
	return [pos, shift]
}

function fastSetbit(bit){
	var pos =  bit >> 3
	var shift = bit % 8
	return [pos, shift]
}

var arr = []
for (var i = 0 ; i < 10000; i ++){
	arr.push(Math.floor( Math.random() * 3000 * 10000))
}
arr.forEach(function(n){
	var s = setbit(n)
	var s1 = fastSetbit(n)
	assert.equal(s[0], s1[0], 's[0]:' + s[0] + '=s1[0]' + s1[0])
	assert.equal(s[1], s1[1], 's[1]:' + s[1] + '=s1[1]' + s1[1])
})
var start = new Date
arr.forEach(function(n){
	setbit(n)
})
console.log('setbit cost: %dms', new Date - start)

var start = new Date
arr.forEach(function(n){
	fastSetbit(n)
})
console.log('fastSetbit cost: %dms', new Date - start)