Add a stable diffusion example (#328)

* Start adding a stable-diffusion example.

* Proper computation of the causal mask.

* Add the chunk operation.

* Work in progress: port the attention module.

* Add some dummy modules for conv2d and group-norm, get the attention module to compile.

* Re-enable the 2d convolution.

* Add the embeddings module.

* Add the resnet module.

* Add the unet blocks.

* Add the unet.

* And add the variational auto-encoder.

* Use the pad function from utils.

candle-nn/src/conv.rs

@@ -48,3 +48,84 @@ impl Conv1d {
         }
     }
 }
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Conv2dConfig {
+    pub padding: usize,
+    pub stride: usize,
+}
+
+impl Default for Conv2dConfig {
+    fn default() -> Self {
+        Self {
+            padding: 0,
+            stride: 1,
+        }
+    }
+}
+
+#[allow(dead_code)]
+#[derive(Debug)]
+pub struct Conv2d {
+    weight: Tensor,
+    bias: Option<Tensor>,
+    config: Conv2dConfig,
+}
+
+impl Conv2d {
+    pub fn new(weight: Tensor, bias: Option<Tensor>, config: Conv2dConfig) -> Self {
+        Self {
+            weight,
+            bias,
+            config,
+        }
+    }
+
+    pub fn config(&self) -> &Conv2dConfig {
+        &self.config
+    }
+
+    pub fn forward(&self, _x: &Tensor) -> Result<Tensor> {
+        todo!()
+    }
+}
+
+pub fn conv1d(
+    in_channels: usize,
+    out_channels: usize,
+    kernel_size: usize,
+    cfg: Conv1dConfig,
+    vs: crate::VarBuilder,
+) -> Result<Conv1d> {
+    let init_ws = crate::init::DEFAULT_KAIMING_NORMAL;
+    let ws = vs.get_or_init((out_channels, in_channels, kernel_size), "weight", init_ws)?;
+    let bound = 1. / (in_channels as f64).sqrt();
+    let init_bs = crate::Init::Uniform {
+        lo: -bound,
+        up: bound,
+    };
+    let bs = vs.get_or_init(out_channels, "bias", init_bs)?;
+    Ok(Conv1d::new(ws, Some(bs), cfg))
+}
+
+pub fn conv2d(
+    in_channels: usize,
+    out_channels: usize,
+    kernel_size: usize,
+    cfg: Conv2dConfig,
+    vs: crate::VarBuilder,
+) -> Result<Conv2d> {
+    let init_ws = crate::init::DEFAULT_KAIMING_NORMAL;
+    let ws = vs.get_or_init(
+        (out_channels, in_channels, kernel_size, kernel_size),
+        "weight",
+        init_ws,
+    )?;
+    let bound = 1. / (in_channels as f64).sqrt();
+    let init_bs = crate::Init::Uniform {
+        lo: -bound,
+        up: bound,
+    };
+    let bs = vs.get_or_init(out_channels, "bias", init_bs)?;
+    Ok(Conv2d::new(ws, Some(bs), cfg))
+}