VBCode in Swift

VBCode.swift

import Foundation

// encode single UInt32 number
func vbEncodeNumber(n: UInt32) -> [UInt8] {
    var n = n
    var result = [UInt8]()
    while true {
        let byte = n % 128
        result.insert(UInt8(byte), at: 0)
        if n < 128 {
            break
        }
        n = n / 128
    }
    result[result.count - 1] += 128
    return result
}

// encode UInt32 numbers to VB code numbers
func vbEncode(ns: [UInt32]) -> [UInt8] {
    return ns.flatMap(vbEncodeNumber)
}

// decode VB code numbers to UInt32 numbers
func vbDecode(bytes: [UInt8]) -> [UInt32] {
    var result = [UInt32]()
    var n: UInt32 = 0
    for byte in bytes {
        if byte < 128 {
            n = 128 * n + UInt32(byte)
        } else {
            n = 128 * n + (UInt32(byte) - 128)
            result.append(n)
            n = 0
        }
    }
    return result
}

// single number encode test
func vbEncodeNumberTest() -> Bool {
    let result1 = (vbEncodeNumber(n: 5) == [UInt8(133)])
    let result2 = (vbEncodeNumber(n: 130) == [UInt8(1), UInt8(130)])
    return result1 && result2
}

// VB code encode test
func vbEncodeTest() -> Bool {
    let numbers: [UInt32] = [5, 130, 45, 12, 150]
    let result = vbEncode(ns: numbers)
    return result == [UInt8(133), UInt8(1), UInt8(130), UInt8(173), UInt8(140), UInt8(1), UInt8(150)]
}

// VB code decode test
func vbDecodeTest() -> Bool {
    let bytesteam = [UInt8(133), UInt8(1), UInt8(130), UInt8(173), UInt8(140), UInt8(1), UInt8(150)]
    let result = vbDecode(bytes: bytesteam)
    return result == [5, 130, 45, 12, 150]
}

vbEncodeNumberTest()
vbEncodeTest()
vbDecodeTest()

//let result = (1 ... 1000).map { [$0] }.map(vb_encode).flatMap(vb_decode)
//result == Array(1 ... 1000)


let helloworld = "hello, world".utf8.map{ UInt32($0) }

let encoded = vbEncode(ns: helloworld)
let decoded = vbDecode(bytes: encoded)

helloworld == decoded



// [UInt32] -> String
let uni = helloworld.flatMap(UnicodeScalar.init)
let chars = uni.map(Character.init)
String(chars)