- Modified Conversation to support generating logits for all submitte…

…d tokens, instead of just the final token.

 - Modified Conversation.Sample to accept an offset, indicating which logits to sample.

LLama/Batched/Conversation.cs

@@ -1,6 +1,7 @@
-using System;
+using System;
 using System.Buffers;
 using System.Collections.Generic;
+using System.Linq;
 using System.Runtime.InteropServices;
 using System.Text.Json;
 using LLama.Native;
@@ -15,10 +16,19 @@ public sealed class Conversation
 {
     private ulong _requiredEpoch;
     private LLamaPos _end;
-    private int _batchSampleIndex;
     private bool _disposed;
+
+    /// <summary>
+    /// Indicates if this conversation has been "forked" and may share logits with another conversation.
+    /// </summary>
     private bool _forked;
 
+    /// <summary>
+    /// Stores the indices to sample from. Contains <see cref="_batchSampleCount"/> valid items.
+    /// </summary>
+    private int[] _batchSampleIndices = new int[4];
+    private int _batchSampleCount;
+
     /// <summary>
     /// The executor which this conversation belongs to
     /// </summary>
@@ -108,7 +118,8 @@ public Conversation Fork()
             // logits, so sampling one conversation may mess up the fork! Setting the "forked" flag on both sequences ensures
             // they both copy the logits before the next sampling run, to fix this issue.
             _requiredEpoch = _requiredEpoch,
-            _batchSampleIndex = _batchSampleIndex,
+            _batchSampleIndices = _batchSampleIndices.ToArray(),
+            _batchSampleCount = _batchSampleCount,
             _forked = true,
 
             _end = _end,
@@ -128,20 +139,24 @@ public Conversation Fork()
     /// <summary>
     /// Get the logits from this conversation, ready for sampling
     /// </summary>
+    /// <param name="offset">How far from the <b>end</b> of the previous prompt should logits be sampled. Any value other than 0 requires allLogits to have been set during prompting</param>
     /// <returns></returns>
     /// <exception cref="ObjectDisposedException"></exception>
     /// <exception cref="CannotSampleRequiresPromptException">Thrown if this conversation was not prompted before the previous call to infer</exception>
     /// <exception cref="CannotSampleRequiresInferenceException">Thrown if Infer() must be called on the executor</exception>
-    public Span<float> Sample()
+    public Span<float> Sample(int offset = 0)
     {
         AssertNotDisposed();
 
         if (_requiredEpoch < Executor.Epoch)
             throw new CannotSampleRequiresPromptException();
         if (_requiredEpoch > Executor.Epoch)
             throw new CannotSampleRequiresInferenceException();
-
-        var span = Executor.Context.NativeHandle.GetLogitsIth(_batchSampleIndex);
+        if (offset >= _batchSampleCount)
+            throw new ArgumentException("Cannot sample offset more than the previous prompt count", nameof(offset));
+
+        var index = _batchSampleIndices[_batchSampleCount - offset - 1];
+        var span = Executor.Context.NativeHandle.GetLogitsIth(index);
 
         // If necessary copy the span, to protect it from modification. This is only done when
         // this conversation has been forked in this epoch.
@@ -161,33 +176,21 @@ private void AssertCanBePrompted()
             throw new AlreadyPromptedConversationException();
     }
 
-    /// <summary>
-    /// Add tokens to this conversation
-    /// </summary>
-    /// <param name="input"></param>
-    /// <returns></returns>
-    [Obsolete("Tokenize the text and pass the tokens instead")]
-    public void Prompt(string input, bool addBos, bool special)
-    {
-        AssertCanBePrompted();
-
-        Prompt(Executor.Context.Tokenize(input, addBos, special));
-    }
-
     /// <summary>
     /// Add tokens to this conversation
     /// </summary>
     /// <param name="tokens"></param>
+    /// <param name="allLogits">If true, generate logits for all tokens. If false, only generate logits for the last token.</param>
     /// <returns></returns>
     /// <exception cref="ObjectDisposedException"></exception>
     /// <exception cref="AlreadyPromptedConversationException"></exception>
-    public void Prompt(List<LLamaToken> tokens)
+    public void Prompt(List<LLamaToken> tokens, bool allLogits = false)
     {
         AssertCanBePrompted();
 
 #if NET6_0_OR_GREATER
         var span = CollectionsMarshal.AsSpan(tokens);
-        Prompt(span);
+        Prompt(span, allLogits);
 #else
         // Borrow an array and copy tokens into it
         var arr = ArrayPool<LLamaToken>.Shared.Rent(tokens.Count);
@@ -204,15 +207,16 @@ public void Prompt(List<LLamaToken> tokens)
         }
 #endif
     }
-
+    
     /// <summary>
     /// Add tokens to this conversation
     /// </summary>
     /// <param name="tokens"></param>
+    /// <param name="allLogits">If true, generate logits for all tokens. If false, only generate logits for the last token.</param>
     /// <returns></returns>
     /// <exception cref="ObjectDisposedException"></exception>
     /// <exception cref="AlreadyPromptedConversationException"></exception>
-    public void Prompt(ReadOnlySpan<LLamaToken> tokens)
+    public void Prompt(ReadOnlySpan<LLamaToken> tokens, bool allLogits = false)
     {
         AssertCanBePrompted();
 
@@ -221,8 +225,25 @@ public void Prompt(ReadOnlySpan<LLamaToken> tokens)
             return;
 
         // Add the prompt to the batch
-        for (var i = 0; i < tokens.Length; i++)
-            _batchSampleIndex = Executor.Batch.Add(tokens[i], _end++, ConversationId, i == tokens.Length - 1);
+        if (allLogits)
+        {
+            if (_batchSampleIndices.Length < tokens.Length)
+                _batchSampleIndices = new int[tokens.Length];
+
+            _batchSampleCount = tokens.Length;
+
+            for (var i = 0; i < tokens.Length; i++)
+                _batchSampleIndices[i] = Executor.Batch.Add(tokens[i], _end++, ConversationId, true);
+        }
+        else
+        {
+            _batchSampleCount = 1;
+
+            for (var i = 0; i < tokens.Length; i++)
+                _batchSampleIndices[0] = Executor.Batch.Add(tokens[i], _end++, ConversationId, i == tokens.Length - 1);
+        }
+
+
 
         // Mark this conversation as needing inference/sampling
         _requiredEpoch = Executor.Epoch + 1;