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

Daniel Dunbar daniel_dunbar at apple.com
Mon May 22 11:07:19 CDT 2017

This function isn't something which comes with Foundation, it is supplied by the BSD libraries on Darwin, but those aren't present on Linux.

I recommend looking for a Swift implementation of a high-quality RNG which will meet your needs, rather than trying to rely on a non-portable implementation coming from the base OS.

 - Daniel

> On May 22, 2017, at 8:44 AM, 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.
> 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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