[swift-users] arc4random_uniform on Linux is missing from Foundation??

[Saagar Jha]

Saagar Jha

> On May 22, 2017, at 08:44, Edward Connell via swift-users <swift-users at swift.org> wrote:
> 
> Any ideas when Foundation on Linux will support arc4random_uniform? This is kind of an important function.
> There doesn't seem to be any decent substitute without requiring the installation of libbsd-dev, which turns out to be messy. Currently I am doing this, but glibc random with mod does not produce good quality numbers, due to modulo bias.

Modulo bias is easy to deal with, though, if you force random to produce a range that is a multiple of the range that you’re trying to produce:

guard range > 0 else { return 0 }
var random: Int
repeat {
	random = Int(random())
} while(random > LONG_MAX / range * range)
return random % range

> 
> Has anyone come up with a better solution to get a true uniform distribution that isn't super messy?
>  
> import Foundation
> 
> #if os(Linux)
> 	import Glibc
> #endif
> 
> 
> public func random_uniform(range: Int) -> Int {
> 	guard range > 0 else { return 0 }
> 	#if os(Linux)
> 	  return Int(random()) % range
> 	#else
> 	  return Int(arc4random_uniform(UInt32(range)))
> 	#endif
> }
> 
> 
> Thanks, Ed
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