Adding extended precision ByteVector conversion (#245)

Using extended precision conversion to get any possible AIFF sample rate

Author: benrr101

src/TaglibSharp/Aiff/StreamHeader.cs

@@ -66,7 +66,7 @@ public struct StreamHeader : IAudioCodec, ILosslessAudioCodec
 		/// </summary>
 		/// <remarks>
 		///    This value is stored in bytes (17-26).
-		///    the sample rate at which the sound is to be played back, 
+		///    the sample rate at which the sound is to be played back,
 		///    in sample frames per second
 		/// </remarks>
 		readonly ulong sample_rate;
@@ -120,7 +120,7 @@ public struct StreamHeader : IAudioCodec, ILosslessAudioCodec
 		/// </exception>
 		/// <exception cref="CorruptFileException">
 		///    <paramref name="data" /> does not begin with <see
-		///    cref="FileIdentifier" /> 
+		///    cref="FileIdentifier" />
 		/// </exception>
 		public StreamHeader (ByteVector data, long streamLength)
 		{
@@ -138,54 +138,7 @@ public StreamHeader (ByteVector data, long streamLength)
 			channels = data.Mid (8, 2).ToUShort (true);
 			total_frames = data.Mid (10, 4).ToULong (true);
 			bits_per_sample = data.Mid (14, 2).ToUShort (true);
-
-			ByteVector sample_rate_indicator = data.Mid (17, 1);
-			ulong sample_rate_tmp = data.Mid (18, 2).ToULong (true);
-			sample_rate = 44100; // Set 44100 as default sample rate
-
-			// The following are combinations that iTunes 8 encodes to.
-			// There may be other combinations in the field, but i couldn't test them.
-			switch (sample_rate_tmp) {
-			case 44100:
-				if (sample_rate_indicator == 0x0E) {
-					sample_rate = 44100;
-				} else if (sample_rate_indicator == 0x0D) {
-					sample_rate = 22050;
-				} else if (sample_rate_indicator == 0x0C) {
-					sample_rate = 11025;
-				}
-				break;
-
-			case 48000:
-				if (sample_rate_indicator == 0x0E) {
-					sample_rate = 48000;
-				} else if (sample_rate_indicator == 0x0D) {
-					sample_rate = 24000;
-				}
-				break;
-
-			case 64000:
-				if (sample_rate_indicator == 0x0D) {
-					sample_rate = 32000;
-				} else if (sample_rate_indicator == 0x0C) {
-					sample_rate = 16000;
-				} else if (sample_rate_indicator == 0x0B) {
-					sample_rate = 8000;
-				}
-				break;
-
-			case 44510:
-				if (sample_rate_indicator == 0x0D) {
-					sample_rate = 22255;
-				}
-				break;
-
-			case 44508:
-				if (sample_rate_indicator == 0x0C) {
-					sample_rate = 11127;
-				}
-				break;
-			}
+			sample_rate = (ulong)data.Mid (16, 10).ToExtendedPrecision ();
 		}
 
 		#endregion

src/TaglibSharp/ByteVector.cs

@@ -757,7 +757,7 @@ public bool ContainsAt (ByteVector pattern, int offset, int patternOffset, int p
 				patternLength = pattern.Count;
 			}
 
-			// do some sanity checking -- all of these things are 
+			// do some sanity checking -- all of these things are
 			// needed for the search to be valid
 			if (patternLength > data.Count ||
 				offset >= data.Count ||
@@ -1398,6 +1398,43 @@ public double ToDouble ()
 			return ToDouble (true);
 		}
 
+		/// <summary>
+		///    Converts the first 10 bytes of the current instance to an IEEE
+		///    754 80-bit extended precision floating point number, expressed
+		///    as a <see cref="double"/>.
+		/// </summary>
+		/// <returns>
+		///    A <see cref="double"/> value containing the value read from the
+		///    current instance.
+		/// </returns>
+		public double ToExtendedPrecision ()
+		{
+			int exponent = ((this[0] & 0x7F) << 8) | this[1];
+			ulong hiMantissa = ((ulong)this[2] << 24)
+			                   | ((ulong)this[3] << 16)
+			                   | ((ulong)this[4] << 8)
+			                   | this[5];
+			ulong loMantissa = ((ulong)this[6] << 24)
+			                   | ((ulong)this[7] << 16)
+			                   | ((ulong)this[8] << 8)
+			                   | this[9];
+
+			double f;
+			if (exponent == 0 && hiMantissa == 0 && loMantissa == 0) {
+				f = 0;
+			} else {
+				if (exponent == 0x7FFF) {
+					f = double.PositiveInfinity;
+				} else {
+					exponent -= 16383;
+					f = hiMantissa * Math.Pow (2, exponent -= 31);
+					f += loMantissa * Math.Pow (2, exponent -= 32);
+				}
+			}
+
+			return (this[0] & 0x80) != 0 ? -f : f;
+		}
+
 		/// <summary>
 		///    Converts a portion of the current instance to a <see
 		///    cref="string"/> object using a specified encoding.