Start adding the Wuerstchen diffusion pipeline (#843)

* Wuerstchen common bits.

* Add the prior layer.

* Start adding diffnext.

candle-transformers/src/models/wuerstchen/common.rs

@@ -0,0 +1,126 @@
+use candle::{Module, Result, Tensor, D};
+use candle_nn::VarBuilder;
+
+// https://github.com/huggingface/diffusers/blob/19edca82f1ff194c07317369a92b470dbae97f34/src/diffusers/pipelines/wuerstchen/modeling_wuerstchen_common.py#L22
+#[derive(Debug)]
+pub struct WLayerNorm {
+    inner: candle_nn::LayerNorm,
+}
+
+impl WLayerNorm {
+    pub fn new(size: usize, vb: VarBuilder) -> Result<Self> {
+        let cfg = candle_nn::layer_norm::LayerNormConfig {
+            eps: 1e-6,
+            remove_mean: true,
+            affine: false,
+        };
+        let inner = candle_nn::layer_norm(size, cfg, vb)?;
+        Ok(Self { inner })
+    }
+}
+
+impl Module for WLayerNorm {
+    fn forward(&self, xs: &Tensor) -> Result<Tensor> {
+        xs.permute((0, 2, 3, 1))?
+            .apply(&self.inner)?
+            .permute((0, 3, 1, 2))
+    }
+}
+
+#[derive(Debug)]
+pub struct TimestepBlock {
+    mapper: candle_nn::Linear,
+}
+
+impl TimestepBlock {
+    pub fn new(c: usize, c_timestep: usize, vb: VarBuilder) -> Result<Self> {
+        let mapper = candle_nn::linear(c_timestep, c * 2, vb.pp("mapper"))?;
+        Ok(Self { mapper })
+    }
+
+    pub fn forward(&self, xs: &Tensor, t: &Tensor) -> Result<Tensor> {
+        let ab = self
+            .mapper
+            .forward(t)?
+            .unsqueeze(2)?
+            .unsqueeze(3)?
+            .chunk(2, 1)?;
+        xs.broadcast_mul(&(&ab[0] + 1.)?)?.broadcast_add(&ab[1])
+    }
+}
+
+#[derive(Debug)]
+pub struct GlobalResponseNorm {
+    gamma: Tensor,
+    beta: Tensor,
+}
+
+impl GlobalResponseNorm {
+    pub fn new(dim: usize, vb: VarBuilder) -> Result<Self> {
+        let gamma = vb.get((1, 1, 1, 1, dim), "gamma")?;
+        let beta = vb.get((1, 1, 1, 1, dim), "beta")?;
+        Ok(Self { gamma, beta })
+    }
+}
+
+impl Module for GlobalResponseNorm {
+    fn forward(&self, xs: &Tensor) -> Result<Tensor> {
+        let agg_norm = xs.sqr()?.sum_keepdim((1, 2))?;
+        let stand_div_norm =
+            agg_norm.broadcast_div(&(agg_norm.mean_keepdim(D::Minus1)? + 1e-6)?)?;
+        (xs.broadcast_mul(&stand_div_norm)?
+            .broadcast_mul(&self.gamma)
+            + &self.beta)?
+            + xs
+    }
+}
+
+#[derive(Debug)]
+pub struct ResBlock {
+    depthwise: candle_nn::Conv2d,
+    norm: WLayerNorm,
+    channelwise_lin1: candle_nn::Linear,
+    channelwise_grn: GlobalResponseNorm,
+    channelwise_lin2: candle_nn::Linear,
+}
+
+impl ResBlock {
+    pub fn new(c: usize, c_skip: usize, ksize: usize, vb: VarBuilder) -> Result<Self> {
+        let cfg = candle_nn::Conv2dConfig {
+            padding: ksize / 2,
+            groups: c,
+            ..Default::default()
+        };
+        let depthwise = candle_nn::conv2d(c + c_skip, c, ksize, cfg, vb.pp("depthwise"))?;
+        let norm = WLayerNorm::new(c, vb.pp("norm"))?;
+        let channelwise_lin1 = candle_nn::linear(c, c * 4, vb.pp("channelwise.0"))?;
+        let channelwise_grn = GlobalResponseNorm::new(c * 4, vb.pp("channelwise.2"))?;
+        let channelwise_lin2 = candle_nn::linear(c * 4, c, vb.pp("channelwise.4"))?;
+        Ok(Self {
+            depthwise,
+            norm,
+            channelwise_lin1,
+            channelwise_grn,
+            channelwise_lin2,
+        })
+    }
+
+    pub fn forward(&self, xs: &Tensor, x_skip: Option<&Tensor>) -> Result<Tensor> {
+        let x_res = xs;
+        let xs = match x_skip {
+            None => xs.clone(),
+            Some(x_skip) => Tensor::cat(&[xs, x_skip], 1)?,
+        };
+        let xs = xs
+            .apply(&self.depthwise)?
+            .apply(&self.norm)?
+            .permute((0, 2, 3, 1))?;
+        let xs = xs
+            .apply(&self.channelwise_lin1)?
+            .gelu()?
+            .apply(&self.channelwise_grn)?
+            .apply(&self.channelwise_lin2)?
+            .permute((0, 3, 1, 2))?;
+        xs + x_res
+    }
+}