我使用了Int.random()方法和arc4random_uniform()来进行数字生成速度测试。 两个测试都在macOS控制台中运行,并且构建配置设置为release。以下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)
}
我得到的时间是 0.029475092887878418(适用于arc4random_uniform(10)) 0.20298802852630615(对于Int.random(in:0 .. <10))
为什么Int.random()这么慢? 有没有办法优化它? 在swift中有没有更快的随机数生成方法?
回答你的第二个问题:
“在swift中有没有更快的随机数生成方法?”
我previously used Xoshiro伪随机数发生器非常快。
这里用于基准测试的代码:
import Foundation
public func randomGen1() {
let n = 1_000_000
var sum: UInt32 = 0
let startTime = CFAbsoluteTimeGetCurrent()
for _ in 0..<n {
sum = sum &+ arc4random_uniform(10)
}
let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
print(sum, timeElapsed)
}
do {
randomGen1()
}
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()
}
Xoshiro很快但没有通过所有随机性测试。如果担心安全性,那么你可以使用Wyhash。
Daniel Lemire(this论文的作者)慷慨地送了我一张Wyhash的Swift implementation:
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
}
}
它可以像这样使用:
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()
}
以下是基准测试结果,在终端中使用优化(-O
)编译代码:
arc4random_uniform() : 0.034s
UInt32.random(in:) : 0.243s
WyHash64 : 0.002s
Xoshiro : 0.001s
你可以找到更多随机数发生器here。