Implement top_p / nucleus sampling (#819)

* Implement top_p / nucleus sampling

* Update changelog

* rustfmt

* Add tests

* Fix clippy warning

* Fix another clippy error

CHANGELOG.md

@@ -4,6 +4,8 @@ This documents the main changes to the `candle` crate.
 ## v0.2.2 - Unreleased
 
 ### Added
+- Support for `top_p` sampling
+  [819](https://github.com/huggingface/candle/pull/819).
 
 ### Modified
 

candle-examples/examples/bigcode/main.rs

@@ -28,9 +28,10 @@ impl TextGeneration {
         tokenizer: Tokenizer,
         seed: u64,
         temp: Option<f64>,
+        top_p: Option<f64>,
         device: &Device,
     ) -> Self {
-        let logits_processor = LogitsProcessor::new(seed, temp);
+        let logits_processor = LogitsProcessor::new(seed, temp, top_p);
         Self {
             model,
             tokenizer,
@@ -94,6 +95,10 @@ struct Args {
     #[arg(long)]
     temperature: Option<f64>,
 
+    /// Nucleus sampling probability cutoff.
+    #[arg(long)]
+    top_p: Option<f64>,
+
     /// The seed to use when generating random samples.
     #[arg(long, default_value_t = 299792458)]
     seed: u64,
@@ -149,7 +154,14 @@ fn main() -> Result<()> {
     let model = GPTBigCode::load(vb, config)?;
     println!("loaded the model in {:?}", start.elapsed());
 
-    let mut pipeline = TextGeneration::new(model, tokenizer, args.seed, args.temperature, &device);
+    let mut pipeline = TextGeneration::new(
+        model,
+        tokenizer,
+        args.seed,
+        args.temperature,
+        args.top_p,
+        &device,
+    );
     pipeline.run(&args.prompt, args.sample_len)?;
     Ok(())
 }

candle-examples/examples/falcon/main.rs

@@ -25,17 +25,25 @@ struct TextGeneration {
     repeat_last_n: usize,
 }
 
+struct GenerationOptions {
+    temp: Option<f64>,
+    top_p: Option<f64>,
+    repeat_penalty: f32,
+    repeat_last_n: usize,
+}
+
 impl TextGeneration {
     fn new(
         model: Falcon,
         tokenizer: Tokenizer,
+        generation_options: GenerationOptions,
         seed: u64,
-        temp: Option<f64>,
         device: &Device,
-        repeat_penalty: f32,
-        repeat_last_n: usize,
     ) -> Self {
-        let logits_processor = LogitsProcessor::new(seed, temp);
+        let logits_processor =
+            LogitsProcessor::new(seed, generation_options.temp, generation_options.top_p);
+        let repeat_penalty = generation_options.repeat_penalty;
+        let repeat_last_n = generation_options.repeat_last_n;
         Self {
             model,
             tokenizer,
@@ -118,6 +126,10 @@ struct Args {
     #[arg(long)]
     temperature: Option<f64>,
 
+    /// Nucleus sampling probability cutoff.
+    #[arg(long)]
+    top_p: Option<f64>,
+
     /// The seed to use when generating random samples.
     #[arg(long, default_value_t = 299792458)]
     seed: u64,
@@ -185,15 +197,14 @@ fn main() -> Result<()> {
     let model = Falcon::load(vb, config)?;
     println!("loaded the model in {:?}", start.elapsed());
 
-    let mut pipeline = TextGeneration::new(
-        model,
-        tokenizer,
-        args.seed,
-        args.temperature,
-        &device,
-        args.repeat_penalty,
-        args.repeat_last_n,
-    );
+    let generation_options = GenerationOptions {
+        temp: args.temperature,
+        top_p: args.top_p,
+        repeat_penalty: args.repeat_penalty,
+        repeat_last_n: args.repeat_last_n,
+    };
+    let mut pipeline =
+        TextGeneration::new(model, tokenizer, generation_options, args.seed, &device);
     pipeline.run(&args.prompt, args.sample_len)?;
     Ok(())
 }

candle-examples/examples/llama/main.rs

@@ -42,6 +42,10 @@ struct Args {
     #[arg(long)]
     temperature: Option<f64>,
 
+    /// Nucleus sampling probability cutoff.
+    #[arg(long)]
+    top_p: Option<f64>,
+
     /// The seed to use when generating random samples.
     #[arg(long, default_value_t = 299792458)]
     seed: u64,
@@ -193,7 +197,7 @@ fn main() -> Result<()> {
 
     println!("starting the inference loop");
     print!("{prompt}");
-    let mut logits_processor = LogitsProcessor::new(args.seed, args.temperature);
+    let mut logits_processor = LogitsProcessor::new(args.seed, args.temperature, args.top_p);
     let start_gen = std::time::Instant::now();
     let mut index_pos = 0;
     let mut token_generated = 0;

candle-examples/examples/llama2-c/main.rs

@@ -27,6 +27,10 @@ struct InferenceCmd {
     #[arg(long)]
     temperature: Option<f64>,
 
+    /// Nucleus sampling probability cutoff.
+    #[arg(long)]
+    top_p: Option<f64>,
+
     #[arg(long, default_value = "")]
     prompt: String,
 
@@ -133,6 +137,7 @@ fn main() -> anyhow::Result<()> {
         None => {
             let cmd = InferenceCmd {
                 temperature: None,
+                top_p: None,
                 prompt: "".to_string(),
                 config: None,
                 model_id: "karpathy/tinyllamas".to_string(),
@@ -256,7 +261,7 @@ fn run_inference(args: &InferenceCmd, common_args: &Args) -> Result<()> {
     let model = Llama::load(vb, &cache, config)?;
 
     println!("starting the inference loop");
-    let mut logits_processor = LogitsProcessor::new(299792458, args.temperature);
+    let mut logits_processor = LogitsProcessor::new(299792458, args.temperature, args.top_p);
     let mut index_pos = 0;
 
     print!("{}", args.prompt);

candle-examples/examples/quantized/main.rs

@@ -71,6 +71,10 @@ struct Args {
     #[arg(long, default_value_t = 0.8)]
     temperature: f64,
 
+    /// Nucleus sampling probability cutoff.
+    #[arg(long)]
+    top_p: Option<f64>,
+
     /// The seed to use when generating random samples.
     #[arg(long, default_value_t = 299792458)]
     seed: u64,
@@ -310,7 +314,7 @@ fn main() -> anyhow::Result<()> {
             prompt_tokens
         };
         let mut all_tokens = vec![];
-        let mut logits_processor = LogitsProcessor::new(args.seed, temperature);
+        let mut logits_processor = LogitsProcessor::new(args.seed, temperature, args.top_p);
 
         let start_prompt_processing = std::time::Instant::now();
         let mut next_token = {

candle-transformers/src/generation/mod.rs

@@ -4,32 +4,76 @@ use rand::{distributions::Distribution, SeedableRng};
 pub struct LogitsProcessor {
     rng: rand::rngs::StdRng,
     temperature: Option<f64>,
+    top_p: Option<f64>,
 }
 
 impl LogitsProcessor {
-    pub fn new(seed: u64, temperature: Option<f64>) -> Self {
+    pub fn new(seed: u64, temperature: Option<f64>, top_p: Option<f64>) -> Self {
         Self {
             rng: rand::rngs::StdRng::seed_from_u64(seed),
             temperature,
+            top_p,
         }
     }
 
+    fn sample_argmax(&mut self, logits: Tensor) -> Result<u32> {
+        let logits_v: Vec<f32> = logits.to_vec1()?;
+        let next_token = logits_v
+            .iter()
+            .enumerate()
+            .max_by(|(_, u), (_, v)| u.total_cmp(v))
+            .map(|(i, _)| i as u32)
+            .unwrap();
+        Ok(next_token)
+    }
+
+    fn sample_multi(&mut self, prs: &Vec<f32>) -> Result<u32> {
+        let distr = rand::distributions::WeightedIndex::new(prs).map_err(Error::wrap)?;
+        let next_token = distr.sample(&mut self.rng) as u32;
+        Ok(next_token)
+    }
+
+    fn sample_topp(&mut self, prs: &mut Vec<f32>, top_p: f32) -> Result<u32> {
+        // top-p sampling (or "nucleus sampling") samples from the smallest set of
+        // tokens that exceed probability top_p. This way we never sample tokens that
+        // have very low probabilities and are less likely to go "off the rails".
+        let mut argsort_indices = (0..prs.len()).collect::<Vec<_>>();
+
+        // Sort by descending probability.
+        argsort_indices.sort_by(|&i, &j| prs[j].partial_cmp(&prs[i]).unwrap());
+
+        // Clamp smaller probabilities to zero.
+        let mut cumsum = 0.;
+        for index in &argsort_indices {
+            if cumsum >= top_p {
+                prs[*index] = 0.0;
+            } else {
+                cumsum += prs[*index];
+            }
+        }
+
+        // Sample with clamped probabilities.
+        let next_token = self.sample_multi(prs)?;
+        Ok(next_token)
+    }
+
     pub fn sample(&mut self, logits: &Tensor) -> Result<u32> {
         let logits = logits.to_dtype(DType::F32)?;
         let temperature = self.temperature.unwrap_or(0.);
-        let next_token = if temperature > 0. {
-            let prs = candle_nn::ops::softmax(&(&logits / temperature)?, D::Minus1)?;
-            let prs: Vec<f32> = prs.to_vec1()?;
-            let distr = rand::distributions::WeightedIndex::new(prs).map_err(Error::wrap)?;
-            distr.sample(&mut self.rng) as u32
+        let top_p = self.top_p.unwrap_or(1.);
+        let next_token = if temperature == 0. {
+            self.sample_argmax(logits)?
         } else {
-            let logits_v: Vec<f32> = logits.to_vec1()?;
-            logits_v
-                .iter()
-                .enumerate()
-                .max_by(|(_, u), (_, v)| u.total_cmp(v))
-                .map(|(i, _)| i as u32)
-                .unwrap()
+            let logits = &(&logits / temperature)?;
+            let prs = candle_nn::ops::softmax(logits, D::Minus1)?;
+            let mut prs: Vec<f32> = prs.to_vec1()?;
+            if top_p <= 0.0 || top_p >= 1.0 {
+                // simply sample from the predicted probability distribution
+                self.sample_multi(&prs)?
+            } else {
+                // top-p (nucleus) sampling, clamping the least likely tokens to zero
+                self.sample_topp(&mut prs, top_p as f32)?
+            }
         };
         Ok(next_token)
     }

candle-transformers/tests/generation_tests.rs

@@ -0,0 +1,29 @@
+use candle::{Device, Result, Tensor};
+use candle_transformers::generation::LogitsProcessor;
+
+#[test]
+fn sample_with_zero_temperature() -> Result<()> {
+    let mut logits_process = LogitsProcessor::new(1337, None, None);
+    let logits = Tensor::new(&[0.1, 0.2, 0.3, 0.4], &Device::Cpu)?;
+    let token = logits_process.sample(&logits)?;
+    assert_eq!(token, 3);
+    Ok(())
+}
+
+#[test]
+fn sample_with_temperature() -> Result<()> {
+    let mut logits_process = LogitsProcessor::new(42, Some(0.9), None);
+    let logits = Tensor::new(&[0.1, 0.2, 0.3, 0.4], &Device::Cpu)?;
+    let token = logits_process.sample(&logits)?;
+    assert_eq!(token, 0);
+    Ok(())
+}
+
+#[test]
+fn sample_with_top_p() -> Result<()> {
+    let mut logits_process = LogitsProcessor::new(42, Some(1.0), Some(0.5));
+    let logits = Tensor::new(&[0.1, 0.2, 0.3, 0.4], &Device::Cpu)?;
+    let token = logits_process.sample(&logits)?;
+    assert_eq!(token, 2);
+    Ok(())
+}

candle-wasm-examples/llama2-c/lib-example.html

@@ -56,6 +56,7 @@
         const weightsURL = `${MODELS_BASE_URL}/${model.url}`;
         const prompt = getValue("prompt");
         const temperature = getValue("temperature");
+        const topP = getValue("top-p");
         const repeatPenalty = getValue("repeat_penalty");
         const seed = getValue("seed");
         const maxSeqLen = getValue("max-seq");
@@ -99,6 +100,7 @@
             tokenizerURL: "tokenizer.json",
             prompt,
             temp: temperature,
+            top_p: topP,
             repeatPenalty,
             seed: BigInt(seed),
             maxSeqLen,
@@ -251,7 +253,7 @@
         <input
           type="range"
           id="max-seq"
-          name="temperature"
+          name="max-seq"
           min="1"
           max="256"
           step="1"
@@ -279,6 +281,22 @@
         >
           0.50</output
         >
+        <label class="text-sm font-medium" for="top-p">Top-p</label>
+        <input
+          type="range"
+          id="top-p"
+          name="top-p"
+          min="0"
+          max="1"
+          step="0.01"
+          value="1.00"
+          oninput="this.nextElementSibling.value = Number(this.value).toFixed(2)"
+        />
+        <output
+          class="text-xs w-[50px] text-center font-light px-1 py-1 border border-gray-700 rounded-md"
+        >
+          1.00</output
+        >
 
         <label class="text-sm font-medium" for="repeat_penalty"
           >Repeat Penalty</label

candle-wasm-examples/llama2-c/src/app.rs

@@ -46,6 +46,7 @@ pub struct App {
     status: String,
     loaded: bool,
     temperature: std::rc::Rc<std::cell::RefCell<f64>>,
+    top_p: std::rc::Rc<std::cell::RefCell<f64>>,
     prompt: std::rc::Rc<std::cell::RefCell<String>>,
     generated: String,
     n_tokens: usize,
@@ -81,6 +82,7 @@ impl Component for App {
             status,
             n_tokens: 0,
             temperature: std::rc::Rc::new(std::cell::RefCell::new(0.)),
+            top_p: std::rc::Rc::new(std::cell::RefCell::new(1.0)),
             prompt: std::rc::Rc::new(std::cell::RefCell::new("".to_string())),
             generated: String::new(),
             current_decode: None,
@@ -122,10 +124,11 @@ impl Component for App {
                     self.n_tokens = 0;
                     self.generated.clear();
                     let temp = *self.temperature.borrow();
+                    let top_p = *self.top_p.borrow();
                     let prompt = self.prompt.borrow().clone();
-                    console_log!("temp: {}, prompt: {}", temp, prompt);
+                    console_log!("temp: {}, top_p: {}, prompt: {}", temp, top_p, prompt);
                     ctx.link()
-                        .send_message(Msg::WorkerInMsg(WorkerInput::Run(temp, prompt)))
+                        .send_message(Msg::WorkerInMsg(WorkerInput::Run(temp, top_p, prompt)))
                 }
                 true
             }
@@ -177,13 +180,21 @@ impl Component for App {
     fn view(&self, ctx: &Context<Self>) -> Html {
         use yew::TargetCast;
         let temperature = self.temperature.clone();
-        let oninput = ctx.link().callback(move |e: yew::InputEvent| {
+        let oninput_temperature = ctx.link().callback(move |e: yew::InputEvent| {
             let input: web_sys::HtmlInputElement = e.target_unchecked_into();
             if let Ok(temp) = f64::from_str(&input.value()) {
                 *temperature.borrow_mut() = temp
             }
             Msg::Refresh
         });
+        let top_p = self.top_p.clone();
+        let oninput_top_p = ctx.link().callback(move |e: yew::InputEvent| {
+            let input: web_sys::HtmlInputElement = e.target_unchecked_into();
+            if let Ok(top_p_input) = f64::from_str(&input.value()) {
+                *top_p.borrow_mut() = top_p_input
+            }
+            Msg::Refresh
+        });
         let prompt = self.prompt.clone();
         let oninput_prompt = ctx.link().callback(move |e: yew::InputEvent| {
             let input: web_sys::HtmlInputElement = e.target_unchecked_into();
@@ -201,9 +212,13 @@ impl Component for App {
                 </p>
                 </div>
                 {"temperature  \u{00a0} "}
-                <input type="range" min="0." max="1.2" step="0.1" value={self.temperature.borrow().to_string()} {oninput} id="temp"/>
+                <input type="range" min="0." max="1.2" step="0.1" value={self.temperature.borrow().to_string()} oninput={oninput_temperature} id="temp"/>
                 {format!(" \u{00a0} {}", self.temperature.borrow())}
                 <br/ >
+                {"top_p  \u{00a0} "}
+                <input type="range" min="0." max="1.0" step="0.05" value={self.top_p.borrow().to_string()} oninput={oninput_top_p} id="top_p"/>
+                {format!(" \u{00a0} {}", self.top_p.borrow())}
+                <br/ >
                 {"prompt: "}<input type="text" value={self.prompt.borrow().to_string()} oninput={oninput_prompt} id="prompt"/>
                 <br/ >
                 {

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

@@ -47,7 +47,7 @@ impl Model {
             tokenizer,
             model: weights,
         });
-        let logits_processor = LogitsProcessor::new(299792458, None);
+        let logits_processor = LogitsProcessor::new(299792458, None, None);
         match model {
             Ok(inner) => Ok(Self {
                 inner,
@@ -69,6 +69,7 @@ impl Model {
         &mut self,
         prompt: String,
         temp: f64,
+        top_p: f64,
         repeat_penalty: f32,
         seed: u64,
     ) -> Result<String, JsError> {
@@ -80,7 +81,12 @@ impl Model {
             }
         }
         let temp = if temp <= 0. { None } else { Some(temp) };
-        self.logits_processor = LogitsProcessor::new(seed, temp);
+        let top_p = if top_p <= 0. || top_p >= 1. {
+            None
+        } else {
+            Some(top_p)
+        };
+        self.logits_processor = LogitsProcessor::new(seed, temp, top_p);
         self.repeat_penalty = repeat_penalty;
         self.tokens.clear();
         let tokens = self

candle-wasm-examples/llama2-c/src/worker.rs

@@ -62,12 +62,18 @@ impl Model {
         link: &WorkerLink<Worker>,
         id: HandlerId,
         temp: f64,
+        top_p: f64,
         prompt: String,
     ) -> Result<()> {
         let dev = Device::Cpu;
         let temp = if temp <= 0. { None } else { Some(temp) };
-        console_log!("{temp:?} {prompt}");
-        let mut logits_processor = LogitsProcessor::new(299792458, temp);
+        let top_p = if top_p <= 0. || top_p >= 1.0 {
+            None
+        } else {
+            Some(top_p)
+        };
+        console_log!("temp: {temp:?} top_p: {top_p:?} prompt: {prompt}");
+        let mut logits_processor = LogitsProcessor::new(299792458, temp, top_p);
         let mut index_pos = 0;
         let mut tokens = self
             .tokenizer
@@ -268,7 +274,7 @@ pub struct Worker {
 #[derive(Serialize, Deserialize)]
 pub enum WorkerInput {
     ModelData(ModelData),
-    Run(f64, String),
+    Run(f64, f64, String),
 }
 
 #[derive(Serialize, Deserialize)]
@@ -301,7 +307,7 @@ impl yew_agent::Worker for Worker {
                 }
                 Err(err) => Err(format!("model creation error {err:?}")),
             },
-            WorkerInput::Run(temp, prompt) => match &mut self.model {
+            WorkerInput::Run(temp, top_p, prompt) => match &mut self.model {
                 None => Err("model has not been set yet".to_string()),
                 Some(model) => {
                     {
@@ -311,7 +317,7 @@ impl yew_agent::Worker for Worker {
                         }
                     }
                     let result = model
-                        .run(&self.link, id, temp, prompt)
+                        .run(&self.link, id, temp, top_p, prompt)
                         .map_err(|e| e.to_string());
                     Ok(WorkerOutput::GenerationDone(result))
                 }