Sketch the candle-transformers crate. (#147)

* Sketch the candle-transformers crate.

* Format the empty files.

candle-transformers/src/generation/mod.rs

@@ -0,0 +1,35 @@
+use candle::{DType, Error, Result, Tensor, D};
+use rand::{distributions::Distribution, SeedableRng};
+
+pub struct LogitsProcessor {
+    rng: rand::rngs::StdRng,
+    temperature: Option<f64>,
+}
+
+impl LogitsProcessor {
+    pub fn new(seed: u64, temperature: Option<f64>) -> Self {
+        Self {
+            rng: rand::rngs::StdRng::seed_from_u64(seed),
+            temperature,
+        }
+    }
+
+    pub fn sample(&mut self, logits: &Tensor) -> Result<u32> {
+        let logits = logits.to_dtype(DType::F32)?;
+        let next_token = if let Some(temperature) = self.temperature {
+            let prs = (&logits / temperature)?.softmax(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
+        } 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()
+        };
+        Ok(next_token)
+    }
+}