Added Reranker example

Cargo.toml

@@ -4,7 +4,7 @@ members = [
     "llama-cpp-sys-2",
     "llama-cpp-2",
     "examples/embeddings",
-    "examples/simple",
+    "examples/simple", "examples/reranker",
 ]
 
 [workspace.dependencies]

examples/reranker/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "reranker"
+version = "0.1.86"
+edition = "2021"
+
+[dependencies]
+llama-cpp-2 = { path = "../../llama-cpp-2", version = "0.1.86" }
+hf-hub = { workspace = true }
+clap = { workspace = true, features = ["derive"] }
+anyhow = { workspace = true }
+encoding_rs = { workspace = true }
+
+[features]
+cuda = ["llama-cpp-2/cuda"]
+metal = ["llama-cpp-2/metal"]
+native = ["llama-cpp-2/native"]
+vulkan = ["llama-cpp-2/vulkan"]
+
+[lints]
+workspace = true

examples/reranker/README.md

@@ -0,0 +1,75 @@
+# Rust Reranker Implementation
+
+A Rust implementation of cross-encoder based reranking using llama-cpp-2. Cross-encoder reranking is a more accurate way to determine similarity between queries and documents compared to traditional embedding-based approaches.
+
+## Overview
+
+This implementation adds a new pooling type `LLAMA_POOLING_TYPE_RANK` which enables cross-encoder based reranking. Unlike traditional embedding approaches that encode query and document separately, this method:
+
+- Processes query and document pairs together in a single pass
+- Directly evaluates semantic relationships between the pairs
+- Outputs raw similarity scores indicating relevance
+
+## Installation
+
+```bash
+# Follow instructions to clone repo.
+# Navigate to examples reranker
+cd examples/reranker
+
+# Build the project
+cargo build --release
+```
+
+## Usage
+
+### Command Line Interface
+
+```bash
+cargo run --release -- \                                                                                                                 ✔ │ 5s │ 12:48:35
+    --model-path "models/bge-reranker-v2-m3.gguf" \ 
+    --query "what is panda?" \
+    --documents "hi" \
+    --documents "it's a bear" \
+    --documents "The giant panda (Ailuropoda melanoleuca), sometimes called a panda bear or simply panda, is a bear species endemic to China." \
+    --pooling rank
+```
+Should output(with bge-reranker-v2-m3-Q5_0): 
+rerank score 0:   -6.551
+rerank score 1:   -3.802
+rerank score 2:    4.522
+
+### CLI Arguments
+
+- `--model-path`: Path to the GGUF model file
+- `--query`: The search query
+- `--documents`: One or more documents to rank against the query
+- `--pooling`: Pooling type (options: none, mean, rank)
+
+### Pooling Types
+
+- `rank`: Performs cross-encoder reranking 
+
+
+Note: The raw scores are not normalized through a sigmoid function. If you need scores between 0-1, you'll need to implement sigmoid normalization in your application code.
+
+# Additional notes
+
+- Query and documents are concatenated using the format <bos>query</eos><sep>answer</eos> 
+
+## Supported Models
+
+Some tested models:
+
+- [BAAI/bge-reranker-v2-m3](https://huggingface.co/BAAI/bge-reranker-v2-m3)
+- [jinaai/jina-reranker-v1-tiny-en](https://huggingface.co/jinaai/jina-reranker-v1-tiny-en)
+
+Not tested others, but anything supported by llama.cpp should work. 
+
+## Implementation Details
+
+This is a close Rust implementation of the reranker implementation discussed in [llama.cpp PR #9510](https://github.com/ggerganov/llama.cpp/pull/9510).
+
+## Potential issues
+
+The bos, eos, sep tokens are being hardcoded. We need to ideally get it from the model and build out the prompts based on each specific model.