From d2c59c565faa631cfc4e2218efa79b7e5a1bc7bb Mon Sep 17 00:00:00 2001
From: Matt Nadareski <mnadareski@outlook.com>
Date: Mon, 18 Nov 2024 11:26:54 -0500
Subject: [PATCH] Make bitstream tests more robust; add notes

---
 .../Streams/ReadOnlyBitStreamTests.cs         | 33 +++++++++++--------
 SabreTools.IO/Streams/ReadOnlyBitStream.cs    | 10 +++---
 2 files changed, 26 insertions(+), 17 deletions(-)

diff --git a/SabreTools.IO.Test/Streams/ReadOnlyBitStreamTests.cs b/SabreTools.IO.Test/Streams/ReadOnlyBitStreamTests.cs
index 815c3da..93bfda5 100644
--- a/SabreTools.IO.Test/Streams/ReadOnlyBitStreamTests.cs
+++ b/SabreTools.IO.Test/Streams/ReadOnlyBitStreamTests.cs
@@ -19,36 +19,43 @@ namespace SabreTools.IO.Test.Streams
         }
 
         [Fact]
-        public void ReadSingleBitBETest()
+        public void ReadSingleBitTest()
         {
             byte[] data = [0b01010101];
             var stream = new ReadOnlyBitStream(new MemoryStream(data));
             byte? bit = stream.ReadBit();
+
             Assert.NotNull(bit);
             Assert.Equal((byte)0b00000001, bit);
             Assert.Equal(1, stream.Position);
         }
 
-        [Fact]
-        public void ReadBitsLETest()
+        [Theory]
+        [InlineData(4, 0b00000101, 1)]
+        [InlineData(9, 0b10101010_1, 2)]
+        public void ReadBitsLETest(int bits, uint expected, int position)
         {
             byte[] data = [0b01010101, 0b01010101, 0b01010101, 0b01010101];
             var stream = new ReadOnlyBitStream(new MemoryStream(data));
-            uint? bits = stream.ReadBitsLE(4);
-            Assert.NotNull(bits);
-            Assert.Equal((byte)0b00001010, bits); // Transcribed to big-endian
-            Assert.Equal(1, stream.Position);
+            uint? actual = stream.ReadBitsLE(bits);
+
+            Assert.NotNull(actual);
+            Assert.Equal(expected, actual);
+            Assert.Equal(position, stream.Position);
         }
 
-        [Fact]
-        public void ReadBitsBETest()
+        [Theory]
+        [InlineData(4, 0b00001010, 1)]
+        [InlineData(9, 0b10101010_1, 2)]
+        public void ReadBitsBETest(int bits, uint expected, int position)
         {
             byte[] data = [0b01010101, 0b01010101, 0b01010101, 0b01010101];
             var stream = new ReadOnlyBitStream(new MemoryStream(data));
-            uint? bits = stream.ReadBitsBE(4);
-            Assert.NotNull(bits);
-            Assert.Equal((byte)0b00001010, bits);
-            Assert.Equal(1, stream.Position);
+            uint? actual = stream.ReadBitsBE(bits);
+
+            Assert.NotNull(actual);
+            Assert.Equal(expected, actual);
+            Assert.Equal(position, stream.Position);
         }
     }
 }
\ No newline at end of file
diff --git a/SabreTools.IO/Streams/ReadOnlyBitStream.cs b/SabreTools.IO/Streams/ReadOnlyBitStream.cs
index dd633a0..8304e7b 100644
--- a/SabreTools.IO/Streams/ReadOnlyBitStream.cs
+++ b/SabreTools.IO/Streams/ReadOnlyBitStream.cs
@@ -91,6 +91,7 @@ namespace SabreTools.IO.Streams
         /// Read a multiple bits in little-endian, if possible
         /// </summary>
         /// <returns>The next bits encoded in a UInt32, null on error or end of stream</returns>
+        /// <remarks>[76543210] order within a byte, appended to output [76543210]</remarks>
         public uint? ReadBitsLE(int bits)
         {
             uint value = 0;
@@ -101,8 +102,8 @@ namespace SabreTools.IO.Streams
                 if (bitValue == null)
                     return null;
 
-                // Add the bit shifted by the current index
-                value += (uint)(bitValue.Value << i);
+                // Append the bit shifted by the current index
+                value |= (uint)(bitValue.Value << i);
             }
 
             return value;
@@ -112,6 +113,7 @@ namespace SabreTools.IO.Streams
         /// Read a multiple bits in big-endian, if possible
         /// </summary>
         /// <returns>The next bits encoded in a UInt32, null on error or end of stream</returns>
+        /// <remarks>[76543210] order within a byte, appended to output [01234567]</remarks>
         public uint? ReadBitsBE(int bits)
         {
             uint value = 0;
@@ -122,8 +124,8 @@ namespace SabreTools.IO.Streams
                 if (bitValue == null)
                     return null;
 
-                // Add the bit shifted by the current index
-                value = (value << 1) + bitValue.Value;
+                // Append the bit shifted by the current index
+                value = (value << 1) | bitValue.Value;
             }
 
             return value;