Implement Span LastIndexOf extension method and add tests (#25748)

* Implement Span LastIndexOf and add tests

* Add LastIndexOfSequence tests and fix implementation

* Vectorize LastIndexOf<byte> similar to IndexOf<byte>

* Add LastIndexOf performance tests

* Adding IndexOf and LastIndexOf tests for reference type (string).

* Use abbreviated version of 'default' literal

* Remove unnecessary type specifiers in generic function calls.

* Cleanup and format all files in the solution to follow coding style.

* Cleaning up leftover unused using directives and extra spaces

3 files changed, 21 insertions, 20 deletions

diff --git a/src/System.Memory/tests/Base64/Base64DecoderUnitTests.cs b/src/System.Memory/tests/Base64/Base64DecoderUnitTests.cs
index 4bc0f20063..15a6733060 100644
--- a/src/System.Memory/tests/Base64/Base64DecoderUnitTests.cs
+++ b/src/System.Memory/tests/Base64/Base64DecoderUnitTests.cs
@@ -24,7 +24,7 @@ namespace System.Buffers.Text.Tests
                 Base64TestHelper.InitalizeDecodableBytes(source, numBytes);
 
                 Span<byte> decodedBytes = new byte[Base64.GetMaxDecodedFromUtf8Length(source.Length)];
-                Assert.Equal(OperationStatus.Done, 
+                Assert.Equal(OperationStatus.Done,
                     Base64.DecodeFromUtf8(source, decodedBytes, out int consumed, out int decodedByteCount));
                 Assert.Equal(source.Length, consumed);
                 Assert.Equal(decodedBytes.Length, decodedByteCount);
@@ -38,7 +38,7 @@ namespace System.Buffers.Text.Tests
             Span<byte> source = Span<byte>.Empty;
             Span<byte> decodedBytes = new byte[Base64.GetMaxDecodedFromUtf8Length(source.Length)];
 
-            Assert.Equal(OperationStatus.Done, 
+            Assert.Equal(OperationStatus.Done,
                 Base64.DecodeFromUtf8(source, decodedBytes, out int consumed, out int decodedByteCount));
             Assert.Equal(source.Length, consumed);
             Assert.Equal(decodedBytes.Length, decodedByteCount);
@@ -62,7 +62,7 @@ namespace System.Buffers.Text.Tests
                 Span<byte> decodedBytes = new byte[Base64.GetMaxDecodedFromUtf8Length(source.Length)];
                 int expectedConsumed = source.Length / 4 * 4; // only consume closest multiple of four since isFinalBlock is false
 
-                Assert.Equal(OperationStatus.NeedMoreData, 
+                Assert.Equal(OperationStatus.NeedMoreData,
                     Base64.DecodeFromUtf8(source, decodedBytes, out int consumed, out int decodedByteCount, isFinalBlock: false));
                 Assert.Equal(expectedConsumed, consumed);
                 Assert.Equal(decodedBytes.Length, decodedByteCount);
@@ -151,7 +151,7 @@ namespace System.Buffers.Text.Tests
             // 123-255
             byte[] invalidBytes = Base64TestHelper.InvalidBytes;
             Assert.Equal(byte.MaxValue + 1 - 64, invalidBytes.Length); // 192
-            
+
             for (int j = 0; j < 8; j++)
             {
                 Span<byte> source = new byte[8] { 50, 50, 50, 50, 80, 80, 80, 80 }; // valid input - "2222PPPP"
@@ -160,14 +160,15 @@ namespace System.Buffers.Text.Tests
                 for (int i = 0; i < invalidBytes.Length; i++)
                 {
                     // Don't test padding (byte 61 i.e. '='), which is tested in DecodingInvalidBytesPadding
-                    if (invalidBytes[i] == Base64TestHelper.s_encodingPad) continue;
+                    if (invalidBytes[i] == Base64TestHelper.s_encodingPad)
+                        continue;
 
                     // replace one byte with an invalid input
                     source[j] = invalidBytes[i];
 
                     Assert.Equal(OperationStatus.InvalidData,
                         Base64.DecodeFromUtf8(source, decodedBytes, out int consumed, out int decodedByteCount));
-                    
+
                     if (j < 4)
                     {
                         Assert.Equal(0, consumed);
@@ -302,7 +303,7 @@ namespace System.Buffers.Text.Tests
                 source[11] = Base64TestHelper.s_encodingPad;
 
                 Span<byte> decodedBytes = new byte[6];
-                Assert.Equal(OperationStatus.DestinationTooSmall, 
+                Assert.Equal(OperationStatus.DestinationTooSmall,
                     Base64.DecodeFromUtf8(source, decodedBytes, out int consumed, out int written));
                 int expectedConsumed = 8;
                 Assert.Equal(expectedConsumed, consumed);
@@ -316,7 +317,7 @@ namespace System.Buffers.Text.Tests
                 source[11] = Base64TestHelper.s_encodingPad;
 
                 Span<byte> decodedBytes = new byte[7];
-                Assert.Equal(OperationStatus.DestinationTooSmall, 
+                Assert.Equal(OperationStatus.DestinationTooSmall,
                     Base64.DecodeFromUtf8(source, decodedBytes, out int consumed, out int written));
                 int expectedConsumed = 8;
                 Assert.Equal(expectedConsumed, consumed);
@@ -335,10 +336,10 @@ namespace System.Buffers.Text.Tests
             int requiredSize = Base64.GetMaxDecodedFromUtf8Length(source.Length);
 
             Span<byte> decodedBytes = new byte[outputSize];
-            Assert.Equal(OperationStatus.DestinationTooSmall, 
+            Assert.Equal(OperationStatus.DestinationTooSmall,
                 Base64.DecodeFromUtf8(source, decodedBytes, out int consumed, out int decodedByteCount));
             int expectedConsumed = decodedBytes.Length / 3 * 4;
-            Assert.Equal(expectedConsumed, consumed);             
+            Assert.Equal(expectedConsumed, consumed);
             Assert.Equal(decodedBytes.Length, decodedByteCount);
             Assert.True(Base64TestHelper.VerifyDecodingCorrectness(expectedConsumed, decodedBytes.Length, source, decodedBytes));
 
@@ -380,7 +381,6 @@ namespace System.Buffers.Text.Tests
             Assert.Throws<ArgumentOutOfRangeException>(() => Base64.GetMaxDecodedFromUtf8Length(int.MinValue));
         }
 
-        
         [Fact]
         public void DecodeInPlace()
         {
@@ -429,7 +429,7 @@ namespace System.Buffers.Text.Tests
         public void DecodeInPlaceInvalidBytes()
         {
             byte[] invalidBytes = Base64TestHelper.InvalidBytes;
-            
+
             for (int j = 0; j < 8; j++)
             {
                 for (int i = 0; i < invalidBytes.Length; i++)
@@ -437,14 +437,15 @@ namespace System.Buffers.Text.Tests
                     Span<byte> buffer = new byte[8] { 50, 50, 50, 50, 80, 80, 80, 80 }; // valid input - "2222PPPP"
 
                     // Don't test padding (byte 61 i.e. '='), which is tested in DecodeInPlaceInvalidBytesPadding
-                    if (invalidBytes[i] == Base64TestHelper.s_encodingPad) continue;
+                    if (invalidBytes[i] == Base64TestHelper.s_encodingPad)
+                        continue;
 
                     // replace one byte with an invalid input
                     buffer[j] = invalidBytes[i];
                     string sourceString = Encoding.ASCII.GetString(buffer.Slice(0, 4).ToArray());
 
                     Assert.Equal(OperationStatus.InvalidData, Base64.DecodeFromUtf8InPlace(buffer, out int bytesWritten));
-                    
+
                     if (j < 4)
                     {
                         Assert.Equal(0, bytesWritten);
@@ -523,7 +524,7 @@ namespace System.Buffers.Text.Tests
                 Span<byte> expectedBytes = Convert.FromBase64String(sourceString);
                 Assert.True(expectedBytes.SequenceEqual(buffer.Slice(0, bytesWritten)));
             }
-            
+
             {
                 Span<byte> buffer = new byte[] { 50, 50, 50, 50, 80, 80, 80, 80 };
                 buffer[7] = Base64TestHelper.s_encodingPad; // valid input - "2222PPP="
diff --git a/src/System.Memory/tests/Base64/Base64EncoderUnitTests.cs b/src/System.Memory/tests/Base64/Base64EncoderUnitTests.cs
index d2e25a497a..c3f5335106 100644
--- a/src/System.Memory/tests/Base64/Base64EncoderUnitTests.cs
+++ b/src/System.Memory/tests/Base64/Base64EncoderUnitTests.cs
@@ -64,7 +64,7 @@ namespace System.Buffers.Text.Tests
         {
             Span<byte> source = Span<byte>.Empty;
             Span<byte> encodedBytes = new byte[Base64.GetMaxEncodedToUtf8Length(source.Length)];
-            
+
             Assert.Equal(OperationStatus.Done, Base64.EncodeToUtf8(source, encodedBytes, out int consumed, out int encodedBytesCount));
             Assert.Equal(source.Length, consumed);
             Assert.Equal(encodedBytes.Length, encodedBytesCount);
@@ -79,7 +79,7 @@ namespace System.Buffers.Text.Tests
             // CLR default limit of 2 gigabytes (GB).
             try
             {
-                 // 1610612734, larger than MaximumEncodeLength, requires output buffer of size 2147483648 (which is > int.MaxValue)
+                // 1610612734, larger than MaximumEncodeLength, requires output buffer of size 2147483648 (which is > int.MaxValue)
                 Span<byte> source = new byte[(int.MaxValue >> 2) * 3 + 1];
                 Span<byte> encodedBytes = new byte[2000000000];
                 Assert.Equal(OperationStatus.DestinationTooSmall, Base64.EncodeToUtf8(source, encodedBytes, out int consumed, out int encodedBytesCount));
@@ -249,7 +249,7 @@ namespace System.Buffers.Text.Tests
         [Fact]
         public void EncodeInPlaceOutputTooSmall()
         {
-            byte[] testBytes = {1, 2, 3};
+            byte[] testBytes = { 1, 2, 3 };
 
             for (int numberOfBytesToTest = 1; numberOfBytesToTest <= testBytes.Length; numberOfBytesToTest++)
             {
@@ -261,7 +261,7 @@ namespace System.Buffers.Text.Tests
         [Fact]
         public void EncodeInPlaceDataLengthTooLarge()
         {
-            byte[] testBytes = {1, 2, 3};
+            byte[] testBytes = { 1, 2, 3 };
             Assert.Equal(OperationStatus.DestinationTooSmall, Base64.EncodeToUtf8InPlace(testBytes, testBytes.Length + 1, out int bytesWritten));
             Assert.Equal(0, bytesWritten);
         }
diff --git a/src/System.Memory/tests/Base64/Base64TestHelper.cs b/src/System.Memory/tests/Base64/Base64TestHelper.cs
index 1026a97683..1aa8271674 100644
--- a/src/System.Memory/tests/Base64/Base64TestHelper.cs
+++ b/src/System.Memory/tests/Base64/Base64TestHelper.cs
@@ -57,7 +57,7 @@ namespace System.Buffers.Text.Tests
                 // Workaroudn for indices.Cast<byte>().ToArray() since it throws
                 // InvalidCastException: Unable to cast object of type 'System.Int32' to type 'System.Byte'
                 byte[] bytes = new byte[indices.Length];
-                for(int i = 0; i < indices.Length; i++)
+                for (int i = 0; i < indices.Length; i++)
                 {
                     bytes[i] = (byte)indices[i];
                 }