Swift 为什么Int.random()比arc4random\u uniform()慢?
我使用Int.random()方法和arc4random_uniform()进行数字生成速度测试。Swift 为什么Int.random()比arc4random\u uniform()慢?,swift,random,Swift,Random,我使用Int.random()方法和arc4random_uniform()进行数字生成速度测试。 这两个测试都在macOS控制台中运行,生成配置设置为release。 下面是我用于测试的代码 public func randomGen1() { let n = 1_000_000 let startTime = CFAbsoluteTimeGetCurrent() for i in 0..<n { _ = arc4random_uniform(10
这两个测试都在macOS控制台中运行,生成配置设置为release。 下面是我用于测试的代码
public func randomGen1() {
let n = 1_000_000
let startTime = CFAbsoluteTimeGetCurrent()
for i in 0..<n {
_ = arc4random_uniform(10)
}
let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
print(timeElapsed)
}
public func randomGen2() {
let n = 1_000_000
let startTime = CFAbsoluteTimeGetCurrent()
for i in 0..<n {
_ = Int.random(in: 0..<10)
}
let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
print(timeElapsed)
}
public func randomGen1(){
设n=1_000_000
让startTime=CFAbsoluteTimeGetCurrent()
对于0中的i..更新
间隔内随机数生成器的实现已合并到标准库中,应比以前更好:
// s = upperBound; r1, r2 = random numbers from generator
func bounded(s: UInt64, r1:UInt64, r2: UInt64) -> UInt64 {
// r1 would come from invoking generator's next()
var m = r1.multipliedFullWidth(by: s)
if m.low < s {
// let t = (0 &- s) % s // Lemire's original form
var t = 0 &- s // O'Neill's modulo optimization
if t >= s {
t &-= s
if t >= s {
t %= s
}
}
while m.low < t {
// r2 would come from invoking generator's next()
m = r2.multipliedFullWidth(by: s)
}
}
return m.high
}
它可以这样使用:
public func randomGen4() {
let n = 1_000_000
var sum: UInt64 = 0
let startTime = CFAbsoluteTimeGetCurrent()
let gen = WyhashGenerator(userSeed: 0)
for _ in 0..<n {
sum = sum &+ gen.random() % 10
}
let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
print(sum, timeElapsed)
}
do {
randomGen4()
}
您可以找到更多的随机数生成器。您使用了哪些优化器设置?查看探查器中的代码,似乎Int.random(in:)
正在内部使用arc4random\u buf
,这似乎比arc4random\u uniform
使用的arc4random\u buf
慢得多。公平地说,arc4random\u uniform()
产生一个UInt32
,因此应该与UInt32.random(in:)
@ielyamani:我试过了,结果没有什么区别。Int.random()和UInt32.random()都计算一个64位的随机数,然后“截断”将结果设置为所需范围。切勿使用CFAbsoluteTimeGetCurrent
:它是一个挂钟,受日历中闰秒的影响。相反,请使用单调时钟:mach\u absolute\u time()
,ProcessInfo.ProcessInfo.systemUptime
,DispatchTime.now()
或CACurrentMediaTime()
。从SystemRandomNumberGenerator
切换到Xoshiro时,请仔细考虑。前者尽可能是加密安全的PRNG。Xoshiro不是加密安全的PRNG。这类事情在突然变得非常重要之前并不重要。CSPRNG的安全性有一个性能指标因此任何合适的非CSPRNG都应该快得多。请注意,RandomNumberGenerator必须实现public mutating func next()->UInt64
,然后您可以调用Int.random(在:0..顺便说一句,这里已经观察到RNG编译时没有所需的方法:。@ielyamani我不认为Big Crush是对CSPRNG(加密安全PRNG)的充分测试。Big Crush只是统计随机性的测试。这比CSPRNG承诺的要小得多。例如,要求它是不切实际的(即超过多项式时间)确定CSPRNG以前的输出,即使您知道它的全部当前内部状态。通过基本统计测试是任何PRNG的表赌注,但没有统计测试可以证明是CSPRNG。Wikipedia的CSPRNG文章对主题IMO不是一个很好的介绍,但它确实包含了一个很好的例子,说明一个好的PRNG完全被破解了a.生成一个种子并使用它选择pi的一个数字。对于每次迭代,输出下一个数字。这对于生成将通过统计测试的随机序列非常好,但是如果您知道PRNG当前正在计算的数字(即PRNG的内部状态),确定之前输出的所有数字很简单。
public func randomGen2() {
let n = 1_000_000
var sum: UInt32 = 0
let startTime = CFAbsoluteTimeGetCurrent()
for _ in 0..<n {
sum = sum &+ UInt32.random(in: 0..<10)
}
let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
print(sum, timeElapsed)
}
do {
randomGen2()
}
struct Xoshiro: RandomNumberGenerator {
public typealias StateType = (UInt32, UInt32, UInt32, UInt32)
private var state: StateType
public init(seed: StateType) {
self.state = seed
}
public mutating func next() -> Int {
let x = state.1 &* 5
let result = ((x &<< 7) | (x &>> 25)) &* 9
let t = state.1 &<< 9
state.2 ^= state.0
state.3 ^= state.1
state.1 ^= state.2
state.0 ^= state.3
state.2 ^= t
state.3 = (state.3 &<< 21) | (state.3 &>> 11)
return Int(result)
}
}
var x = Xoshiro(seed: (UInt32.random(in: 0..<10), //Other upper limits could be used to increase randomness
UInt32.random(in: 0..<10),
UInt32.random(in: 0..<10),
UInt32.random(in: 0..<10)))
public func randomGen3() {
let n = 1_000_000
var sum: UInt32 = 0
let startTime = CFAbsoluteTimeGetCurrent()
for _ in 0..<n {
sum = sum &+ UInt32(abs(x.next()) % 10)
}
let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
print(sum, timeElapsed)
}
do {
randomGen3()
}
class WyhashGenerator {
var seed : UInt64
let multiplier1 : UInt64 = 0xa3b195354a39b70d
let multiplier2 : UInt64 = 0x1b03738712fad5c9
let increment : UInt64 = 0x60bee2bee120fc15
init(userSeed : UInt64) {
seed = userSeed;
}
func random() -> UInt64 {
seed &+= increment
let fullmult1 = seed.multipliedFullWidth(by: multiplier1)
let m1 = fullmult1.high ^ fullmult1.low;
let fullmult2 = m1.multipliedFullWidth(by: multiplier2)
let m2 = fullmult2.high ^ fullmult2.low;
return m2
}
}
public func randomGen4() {
let n = 1_000_000
var sum: UInt64 = 0
let startTime = CFAbsoluteTimeGetCurrent()
let gen = WyhashGenerator(userSeed: 0)
for _ in 0..<n {
sum = sum &+ gen.random() % 10
}
let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
print(sum, timeElapsed)
}
do {
randomGen4()
}
arc4random_uniform() : 0.034s
UInt32.random(in:) : 0.243s
WyHash64 : 0.002s
Xoshiro : 0.001s