SwiftUI code for comparing virtual scrolling performance

iterhash.swift

// Copyright 2022 Google LLC.
// SPDX-License-Identifier: Apache-2.0

// Scrolling test case by Raph Levien

import SwiftUI
import CryptoKit

struct ContentView: View {
    var body: some View {
        ScrollView {
            LazyVStack {
                ForEach(1...10000, id: \.self) { i in
                    Text("\(i): " + iterhash(i))
                }
            }
        }
    }
}

let hex: [UInt8] = [0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66]

func format_hex(_ hash: SHA256, _ buf: inout [UInt8]) {
    var j = 0
    hash.finalize().forEach { byte in
        buf[j] = hex[Int(byte) >> 4]
        buf[j + 1] = hex[Int(byte) & 0xf]
        j += 2
    }
}

func iterhash(_ i: Int) -> String {
    let s = "\(i)"
    var h = SHA256()
    h.update(data: s.data(using: .utf8)!)
    var buf = [UInt8](repeating: 0, count: 64)
    format_hex(h, &buf)
    for _ in 1..<i {
        h = SHA256()
        h.update(data: buf)
        format_hex(h, &buf)
    }
    return String(decoding: buf, as: UTF8.self)
}