Add a repeat penalty to the llama2.c wasm example. (#709)

candle-wasm-examples/llama2-c/src/bin/m.rs

@@ -1,5 +1,6 @@
 use candle::{Device, Tensor};
-use candle_wasm_example_llama2::worker::{LogitsProcessor, Model as M, ModelData};
+use candle_transformers::generation::LogitsProcessor;
+use candle_wasm_example_llama2::worker::{Model as M, ModelData};
 use wasm_bindgen::prelude::*;
 
 #[wasm_bindgen]
@@ -7,14 +8,26 @@ pub struct Model {
     inner: M,
     logits_processor: LogitsProcessor,
     tokens: Vec<u32>,
+    repeat_penalty: f32,
 }
 
 impl Model {
     fn process(&mut self, tokens: &[u32]) -> candle::Result<String> {
+        const REPEAT_LAST_N: usize = 64;
         let dev = Device::Cpu;
         let input = Tensor::new(tokens, &dev)?.unsqueeze(0)?;
         let logits = self.inner.llama.forward(&input, tokens.len())?;
         let logits = logits.squeeze(0)?;
+        let logits = if self.repeat_penalty == 1. {
+            logits
+        } else {
+            let start_at = self.tokens.len().saturating_sub(REPEAT_LAST_N);
+            candle_transformers::utils::apply_repeat_penalty(
+                &logits,
+                self.repeat_penalty,
+                &tokens[start_at..],
+            )?
+        };
 
         let next_token = self.logits_processor.sample(&logits)?;
         self.tokens.push(next_token);
@@ -40,13 +53,19 @@ impl Model {
                 inner,
                 logits_processor,
                 tokens: vec![],
+                repeat_penalty: 1.,
             }),
             Err(e) => Err(JsError::new(&e.to_string())),
         }
     }
 
     #[wasm_bindgen]
-    pub fn init_with_prompt(&mut self, prompt: String, temp: f64) -> Result<String, JsError> {
+    pub fn init_with_prompt(
+        &mut self,
+        prompt: String,
+        temp: f64,
+        repeat_penalty: f32,
+    ) -> Result<String, JsError> {
         // First reset the cache.
         {
             let mut cache = self.inner.cache.kvs.lock().unwrap();
@@ -56,6 +75,7 @@ impl Model {
         }
         let temp = if temp <= 0. { None } else { Some(temp) };
         self.logits_processor = LogitsProcessor::new(299792458, temp);
+        self.repeat_penalty = repeat_penalty;
         self.tokens.clear();
         let tokens = self
             .inner