Fixed decoding of large tokens (over 16 bytes) in streaming text decoder

LLama.Unittest/StreamingTextDecoderTests.cs

@@ -0,0 +1,53 @@
+using System.Text;
+using LLama.Common;
+using Xunit.Abstractions;
+
+namespace LLama.Unittest;
+
+public class StreamingTextDecoderTests
+    : IDisposable
+{
+    private readonly LLamaWeights _model;
+    private readonly ITestOutputHelper _testOutputHelper;
+    private readonly ModelParams _params;
+
+    public StreamingTextDecoderTests(ITestOutputHelper testOutputHelper)
+    {
+        _testOutputHelper = testOutputHelper;
+        _params = new ModelParams(Constants.ModelPath);
+        _model = LLamaWeights.LoadFromFile(_params);
+    }
+
+    public void Dispose()
+    {
+        _model.Dispose();
+    }
+
+    [Fact]
+    public void DecodesSimpleText()
+    {
+        var decoder = new StreamingTokenDecoder(Encoding.UTF8, _model);
+
+        const string text = "The cat sat on the mat";
+        var tokens = _model.NativeHandle.Tokenize(text, false, false, Encoding.UTF8);
+
+        foreach (var lLamaToken in tokens)
+            decoder.Add(lLamaToken);
+
+        Assert.Equal(text, decoder.Read().Trim());
+    }
+
+    [Fact]
+    public void DecodesComplexText()
+    {
+        var decoder = new StreamingTokenDecoder(Encoding.UTF8, _model);
+
+        const string text = "猫坐在垫子上 😀🤨🤐😏";
+        var tokens = _model.NativeHandle.Tokenize(text, false, false, Encoding.UTF8);
+
+        foreach (var lLamaToken in tokens)
+            decoder.Add(lLamaToken);
+
+        Assert.Equal(text, decoder.Read().Trim());
+    }
+}

LLama/Native/SafeLLamaContextHandle.cs

@@ -194,7 +194,7 @@ namespace LLama.Native
         /// <param name="token">Token to decode</param>
         /// <param name="dest">A span to attempt to write into. If this is too small nothing will be written</param>
         /// <returns>The size of this token. **nothing will be written** if this is larger than `dest`</returns>
-        public int TokenToSpan(LLamaToken token, Span<byte> dest)
+        public uint TokenToSpan(LLamaToken token, Span<byte> dest)
         {
             return ThrowIfDisposed().TokenToSpan(token, dest);
         }

LLama/Native/SafeLlamaModelHandle.cs

@@ -126,10 +126,10 @@ namespace LLama.Native
         /// <param name="token">Token to decode</param>
         /// <param name="dest">A span to attempt to write into. If this is too small nothing will be written</param>
         /// <returns>The size of this token. **nothing will be written** if this is larger than `dest`</returns>
-        public int TokenToSpan(LLamaToken token, Span<byte> dest)
+        public uint TokenToSpan(LLamaToken token, Span<byte> dest)
         {
             var length = NativeApi.llama_token_to_piece(this, token, dest);
-            return Math.Abs(length);
+            return (uint)Math.Abs(length);
         }
 
         /// <summary>

LLama/StreamingTokenDecoder.cs

@@ -113,19 +113,19 @@ namespace LLama
                 // Try to get bytes
                 var l = model.TokenToSpan(token, bytes);
 
-                // Negative length indicates that the output was too small. Expand it to twice that size and try again.
-                if (l < 0)
+                // Check if the length was larger than the buffer. If so expand the buffer and try again
+                if (l > bytes.Length)
                 {
                     // Return the old array to the pool and get a new one
                     ArrayPool<byte>.Shared.Return(bytes);
-                    bytes = ArrayPool<byte>.Shared.Rent(-l * 2);
+                    bytes = ArrayPool<byte>.Shared.Rent((int)(l * 2));
 
                     // Get bytes, this time it can't fail
                     l = model.TokenToSpan(token, bytes);
                 }
 
-                Debug.Assert(l >= 0);
-                return new Span<byte>(bytes, 0, l);
+                Debug.Assert(l <= bytes.Length);
+                return new Span<byte>(bytes, 0, (int)l);
             }
         }