Refactor Base32 encoder

Sources/ULID/Data+Base32.swift

@@ -33,32 +33,16 @@ enum Base32 {
 
 }
 
-enum Base32Error: Error {
-    case invalidCharacter
-}
-
 extension Data {
 
     /// Decode Crockford's Base32
     init?(base32Encoded base32String: String, using table: [UInt8] = Base32.crockfordsDecodingTable) {
-        guard base32String.unicodeScalars.allSatisfy({ $0.isASCII }) else {
-            return nil
-        }
-
         var base32String = base32String
         while let last = base32String.last, last == "=" {
             base32String.removeLast()
         }
-        guard [0, 2, 4, 5, 7].contains(base32String.count % 8) else {
-            return nil
-        }
 
-        let dstlen = base32String.count * 5 / 8
+        let result: Data? = base32String.withCString(encodedAs: Unicode.ASCII.self) { (src) in
-
-        var buffer = Data(count: dstlen)
-
-        let success: Bool = buffer.withUnsafeMutableBytes { (dst: UnsafeMutablePointer<UInt8>) in
-            base32String.withCString(encodedAs: Unicode.ASCII.self) { (src) in
             func _strlen(_ str: UnsafePointer<UInt8>) -> Int {
                 var str = str
                 var i = 0
@@ -69,7 +53,16 @@ extension Data {
                 return i
             }
 
-                var srcleft = _strlen(src)
+            let srclen = _strlen(src)
+            guard [0, 2, 4, 5, 7].contains(srclen % 8) else {
+                return nil
+            }
+
+            let dstlen = srclen * 5 / 8
+
+            var buffer = Data(count: dstlen)
+            let success: Bool = buffer.withUnsafeMutableBytes { (dst: UnsafeMutablePointer<UInt8>) in
+                var srcleft = srclen
                 var srcp = src
 
                 var dstp = dst
@@ -112,12 +105,19 @@ extension Data {
 
                 return true
             }
-        }
+
             guard success else {
                 return nil
             }
 
-        self = buffer
+            return buffer
+        }
+
+        guard let data = result else {
+            return nil
+        }
+
+        self = data
     }
 
     /// Encode Crockford's Base32