Add conversion initializers from ByteReader to Lsb/MsbBitReader

Author: tsolomko

Sources/BitReader.swift

@@ -14,6 +14,8 @@ public protocol BitReader: class {
     /// Creates an instance for reading bits (and bytes) from `data`.
     init(data: Data)
 
+    // TODO: Add `init(_ byteReader: ByteReader)`?
+
     /// Reads bit and returns it, advancing by one BIT position.
     func bit() -> UInt8
 

Sources/LsbBitReader.swift

@@ -5,10 +5,7 @@
 
 import Foundation
 
-/**
- A type that contains functions for reading `Data` bit-by-bit and byte-by-byte,
- assuming "LSB 0" bit numbering scheme.
- */
+/// A type that contains functions for reading `Data` bit-by-bit and byte-by-byte, assuming "LSB0" bit numbering scheme.
 public final class LsbBitReader: ByteReader, BitReader {
 
     private var bitMask: UInt8 = 1
@@ -28,6 +25,16 @@ public final class LsbBitReader: ByteReader, BitReader {
         super.init(data: data)
     }
 
+    /**
+     Converts a `ByteReader` instance into `LsbBitReader`, enabling bits reading capabilities.
+     Current `offset` value in `byteReader` is preserved.
+     */
+    public init(_ byteReader: ByteReader) {
+        self.currentByte = byteReader.offset < byteReader.data.endIndex ? byteReader.data[byteReader.offset] : 0
+        super.init(data: byteReader.data)
+        self.offset = byteReader.offset
+    }
+
     /// True, if reader's BIT pointer is aligned with the BYTE border.
     public var isAligned: Bool {
         return self.bitMask == 1

Sources/MsbBitReader.swift

@@ -5,10 +5,7 @@
 
 import Foundation
 
-/**
- A type that contains functions for reading `Data` bit-by-bit and byte-by-byte,
- assuming "MSB 0" bit numbering scheme.
- */
+/// A type that contains functions for reading `Data` bit-by-bit and byte-by-byte, assuming "MSB0" bit numbering scheme.
 public final class MsbBitReader: ByteReader, BitReader {
 
     private var bitMask: UInt8 = 128
@@ -28,6 +25,16 @@ public final class MsbBitReader: ByteReader, BitReader {
         super.init(data: data)
     }
 
+    /**
+     Converts a `ByteReader` instance into `MsbBitReader`, enabling bit reading capabilities.
+     Current `offset` value in `byteReader` is preserved.
+     */
+    public init(_ byteReader: ByteReader) {
+        self.currentByte = byteReader.offset < byteReader.data.endIndex ? byteReader.data[byteReader.offset] : 0
+        super.init(data: byteReader.data)
+        self.offset = byteReader.offset
+    }
+
     /// True, if reader's BIT pointer is aligned with the BYTE border.
     public var isAligned: Bool {
         return self.bitMask == 128