A base converter in Swift 3. For instance, BaseConverter.representNumber(number: 3405691582, inBase: 16) is "cafebabe"

BaseConverter.swift

import Foundation

public struct BaseConverter
{
    static let alphabet = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" // 62 digits
    
    static func representNumber(n: Int, asciiAlphabet: String) -> String
    {
        let base = asciiAlphabet.lengthOfBytes(using: String.Encoding.utf8)
        if (n < base){
            return asciiSubstringOf(string: asciiAlphabet, start: n, end: n + 1)
        } else {
            // Get the number minus the last digit and do a recursive call.
            // Note that division between integer drops the decimals, eg: 769/10 = 76
            let newNumber = Int(trunc(Double(n / base)))
            let digit1 = representNumber(n: newNumber, asciiAlphabet: asciiAlphabet)
            let nModBase = n % base
            let digit2 = asciiSubstringOf(string: asciiAlphabet, start: nModBase, end: nModBase + 1)
            return "\(digit1)\(digit2)"
        }
    }

    static func representNumber(number: Int, inBase base: Int) -> String
    {
        let length = alphabet.lengthOfBytes(using: String.Encoding.ascii)
        assert(length >= Int(base), "Not enough characters. Use base \(length) or lower.")
        let subAlphabet = asciiSubstringOf(string: alphabet, start: 0, end: base)
        let representation = representNumber(n: number, asciiAlphabet: subAlphabet)
        print("number \(number) represented in base \(base) using alphabet \(subAlphabet) is \(representation)")
        return representation
    }
    
    static func asciiSubstringOf(string: String, start: Int, end: Int) -> String
    {
        assert(start <= end)
        let length = string.lengthOfBytes(using: String.Encoding.ascii)
        if end > length {
            return ""
        }
        let lo = string.index(string.startIndex, offsetBy: start)
        let hi = string.index(string.startIndex, offsetBy: end)
        let substring = string.substring(with: lo..<hi)
        return substring
    }
    
}