Add CharSet bytesNeeded

Author: dingosky

EntropyString.podspec

@@ -2,17 +2,17 @@
 
 Pod::Spec.new do |s|
   s.name         = "EntropyString"
-  s.version      = "2.0.1"
+  s.version      = "2.1.0"
   s.summary      = "Efficiently generate cryptographically strong random strings of specified entropy from various character sets."
 
-  s.description  = <<-DESC
+  s.description = <<-DESC
 Efficiently generate cryptographically strong and secure random strings of specified entropy from various character sets for use when probabilisticly unique string identifiers are needed. Entropy is calculated from a total number of strings and acceptable risk of a repeat.
                    DESC
 
-  s.homepage = "https://github.com/#{s.name}/#{s.name}-Swift"
-  s.license  = { :type => "MIT", :file => "LICENSE" }
-  s.authors   = { "knoxen" => "paul@knoxen.com", "dingo sky" => "paul@dingosky.com" }
-  s.social_media_url   = "http://twitter.com/knoxen"
+  s.homepage = "https://github.com/EntropyString/EntropyString-Swift"
+  s.license = { :type => "MIT", :file => "LICENSE" }
+  s.authors = { "knoxen" => "paul@knoxen.com", "dingo sky" => "paul@dingosky.com" }
+  s.social_media_url = "http://twitter.com/knoxen"
 
   s.ios.deployment_target = "9.0"
   s.osx.deployment_target = "10.11"
@@ -21,7 +21,7 @@ Efficiently generate cryptographically strong and secure random strings of speci
 
   s.source = { :git => "https://github.com/EntropyString/EntropyString-Swift.git", :tag => "#{s.version}" }
 
-  s.source_files  = "Sources/**/*.swift"
+  s.source_files = "Sources/*.swift"
 #   s.public_header_files = "#{s.name}/{s.name}.h"
 
 end

Sources/Bytes.swift

@@ -26,12 +26,12 @@
 //
 import Foundation
 
-public struct Bytes {
+internal struct Bytes {
   #if os(Linux)
   // On first use will attempt to load `arc4random_buf`
   private typealias Arc4Random_Buf = @convention(c) (ImplicitlyUnwrappedOptional<UnsafeMutableRawPointer>, Int) -> ()
   private var arc4random_buf: Arc4Random_Buf?
-  public static var instance = Bytes()
+  private static var instance = Bytes()
 
   private init() {
     if let handle = dlopen(nil, RTLD_NOW), let result = dlsym(handle, "arc4random_buf") {
@@ -42,21 +42,18 @@ public struct Bytes {
 
   /// Generates random bytes
   ///
-  /// The number of bytes returned is sufficient to generate _count_ characters from the `charSet`.
+  /// The number of bytes returned is sufficient to generate a string with `bits` of entropy using `CharSet`
   ///
-  /// - parameter count: The number of characters that can be generated.
+  /// - parameter bits: Entropy bits
   /// - paramater charSet: The character set that will be used.
   /// - parameter secRand: On Apple OSes, if _secRand_ is `true`, attempt to use `SecRandomCopyBytes` to
   ///     generate random bytes; if `false` use `arc4random_buf`. This parameter is ignored on Linux OS.
   ///
   /// - return: Random bytes. On Apple OSes, if _secRand_ is passed as `true`, the value on return
   ///     indicates whether `SecRandomCopyBytes` (`true`) or `arc4random_buf` (`false`) was used.
   ///
-  static func random(_ count: UInt, _ entropyBits: UInt8, _ secRand: inout Bool) -> [UInt8] {
-    // Each slice forms a chars and requires entropy per char bits
-    let bytesPerSlice = Double(entropyBits) / Double(Entropy.bitsPerByte)
-    
-    let bytesNeeded = Int(ceil(Double(count) * bytesPerSlice))
+  static func random(_ bits: Float, _ charSet: CharSet, _ secRand: inout Bool) -> [UInt8] {
+    let bytesNeeded = charSet.bytesNeeded(bits: bits)
     var bytes = [UInt8](repeating: 0, count: bytesNeeded)
 
     #if os(Linux)

Sources/CharSet.swift

@@ -59,7 +59,12 @@ public struct CharSet {
       ndxFn = CharSet.ndxFnForNonDivisor(bitsPerChar)
     }
   }
-
+  
+  public func bytesNeeded(bits: Float) -> Int {
+    let count = ceil(bits / Float(bitsPerChar))
+    return Int(ceil(count * Float(bitsPerChar) / Float(Entropy.bitsPerByte)))
+  }
+  
   /// Determines index into `CharSet` characters when base is a multiple of 8.
   ///
   /// Each `slice` of bits is used to create a single character. A `chunk` is the number of

Sources/Random.swift

@@ -96,13 +96,12 @@ public class Random {
   ///     If _secRand_ is passed in as `true`, the value of _secRand_ on return indicates whether
   ///     `SecRandomCopyBytes` (`true`) or `arc4random_buf` (`false`) was used.
   public func string(bits: Float, secRand: inout Bool) -> String {
-    let count: UInt = UInt(ceil(bits / Float(charSet.bitsPerChar)))
-    guard 0 < count else { return "" }
+    guard 0 < bits else { return "" }
 
-    // genBytes sets secRand
-    let bytes = Bytes.random(count, charSet.bitsPerChar, &secRand)
+    // `Bytes.random` sets `secRand`
+    let bytes = Bytes.random(bits, charSet, &secRand)
 
-    // genBytes ensures enough bytes so this call will not fail
+    // `Bytes.random` ensures enough bytes so this call will not fail
     return try! string(bits: bits, using: bytes)
   }
 
@@ -143,6 +142,8 @@ public class Random {
     return string
   }
 
+  // MARK: - Private
+  
   /// Gets a character from the current `CharSet` characters.
   ///
   /// - parameter ndx: The index of the character

Tests/EntropyStringTests/CharSetTests.swift

@@ -87,7 +87,27 @@ class CharSetTests: XCTestCase {
       }
     }
   }
+  
+  func testBytesNeeded() {
+    let doTest: (CharSet, Float) -> () = { (charSet: CharSet, bits: Float) -> () in
+      let bytesNeeded = charSet.bytesNeeded(bits: bits)
+      let atLeast = Int(ceil(bits / Float(Entropy.bitsPerByte)))
+      XCTAssertTrue(atLeast <= bytesNeeded)
+      let atMost = atLeast + 1
+      XCTAssertTrue(bytesNeeded <= atMost)
+    }
 
+    let charSets = [.charSet64, .charSet32, .charSet16, .charSet8,  .charSet4,  .charSet2] as [CharSet]
+    for charSet in charSets {
+      for bits in 0 ... 10 {
+        doTest(charSet, Float(bits))
+      }
+      for bits in stride(from: 12, through: 132, by: 5) {
+        doTest(charSet, Float(bits))
+      }
+    }
+  }
+  
   func testStatics() {
     XCTAssertNotNil(CharSet.charSet64)
     XCTAssertNotNil(CharSet.charSet32)

Tests/EntropyStringTests/RandomTests.swift

@@ -11,7 +11,7 @@ import XCTest
 
 class RandomTests: XCTestCase {
   var random: Random!
-  var charSets = [.charSet64, .charSet32, .charSet16, .charSet8,  .charSet4,  .charSet2] as [CharSet]
+  let charSets = [.charSet64, .charSet32, .charSet16, .charSet8,  .charSet4,  .charSet2] as [CharSet]
 
   func testInit() {
     let random = Random()