https://github.com/ensan-hcl/swift-for-each-performance

RandomUInt8Sequence.swift

public struct RandomUInt8Sequence: Sequence {
    @usableFromInline var count: Int
    public init(count: Int) {
        self.count = count
    }
    public func makeIterator() -> Iterator {
        Iterator(self)
    }
    
    public struct Iterator: IteratorProtocol {
        private var count: Int
        private var current: Int = 0
        private var buf: (UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8) = (0, 0, 0, 0, 0, 0, 0, 0)

        init(_ wrapped: RandomUInt8Sequence) {
            self.count = wrapped.count
        }

        public mutating func next() -> UInt8? {
            guard current < count else {
                return nil
            }
            defer {
                self.current += 1
            }

            let i = self.current % 8
            if i == 0 {
                withUnsafeMutableBytes(of: &buf) { p in
                    p.bindMemory(to: UInt64.self).baseAddress!.pointee = UInt64.random(in: .min ... .max)
                }
            }

            return withUnsafeBytes(of: &buf) { p in
                p[i]
            }
        }

        public typealias Element = UInt8
    }

    @inlinable public func forEachSpecial(_ body: (Self.Element) throws -> Void) rethrows {
        print("Using special forEach")
        var i = 0
        while i + 8 < count {
            var rand = UInt64.random(in: .min ... .max)
            try withUnsafeBytes(of: &rand) { bytes in
                for byte in bytes {
                    try body(byte)
                }
            }
            i += 8
        }
        for _ in i ..< count {
            try body(UInt8.random(in: .min ... .max))
        }
    }
}