1 files changed, 221 insertions, 0 deletions
diff --git a/vendor/jpeg-decoder/src/worker/rayon.rs b/vendor/jpeg-decoder/src/worker/rayon.rs
new file mode 100644
index 0000000..ec7df25
--- /dev/null
+++ b/vendor/jpeg-decoder/src/worker/rayon.rs
@@ -0,0 +1,221 @@
+use core::convert::TryInto;
+
+use rayon::iter::{IndexedParallelIterator, ParallelIterator};
+use rayon::slice::ParallelSliceMut;
+
+use crate::decoder::{choose_color_convert_func, ColorTransform};
+use crate::error::Result;
+use crate::idct::dequantize_and_idct_block;
+use crate::parser::Component;
+use crate::upsampler::Upsampler;
+use crate::{decoder::MAX_COMPONENTS, parser::Dimensions};
+
+use std::sync::Arc;
+
+use super::{RowData, Worker};
+
+/// Technically similar to `immediate::ImmediateWorker` but we copy it since we may prefer
+/// different style of managing the memory allocation, something that multiple actors can access in
+/// parallel.
+#[derive(Default)]
+struct ImmediateWorker {
+    offsets: [usize; MAX_COMPONENTS],
+    results: [Vec<u8>; MAX_COMPONENTS],
+    components: [Option<Component>; MAX_COMPONENTS],
+    quantization_tables: [Option<Arc<[u16; 64]>>; MAX_COMPONENTS],
+}
+
+#[derive(Clone, Copy)]
+struct ComponentMetadata {
+    block_width: usize,
+    block_count: usize,
+    line_stride: usize,
+    dct_scale: usize,
+}
+
+#[derive(Default)]
+pub struct Scoped {
+    inner: ImmediateWorker,
+}
+
+impl ImmediateWorker {
+    pub fn start_immediate(&mut self, data: RowData) {
+        let elements = data.component.block_size.width as usize
+            * data.component.block_size.height as usize
+            * data.component.dct_scale
+            * data.component.dct_scale;
+        self.offsets[data.index] = 0;
+        self.results[data.index].resize(elements, 0u8);
+        self.components[data.index] = Some(data.component);
+        self.quantization_tables[data.index] = Some(data.quantization_table);
+    }
+
+    pub fn get_result_immediate(&mut self, index: usize) -> Vec<u8> {
+        core::mem::take(&mut self.results[index])
+    }
+
+    pub fn component_metadata(&self, index: usize) -> Option<ComponentMetadata> {
+        let component = self.components[index].as_ref()?;
+        let block_size = component.block_size;
+        let block_width = block_size.width as usize;
+        let block_count = block_size.width as usize * component.vertical_sampling_factor as usize;
+        let line_stride = block_size.width as usize * component.dct_scale;
+        let dct_scale = component.dct_scale;
+
+        Some(ComponentMetadata {
+            block_width,
+            block_count,
+            line_stride,
+            dct_scale,
+        })
+    }
+
+    pub fn append_row_locked(
+        quantization_table: Arc<[u16; 64]>,
+        metadata: ComponentMetadata,
+        data: Vec<i16>,
+        result_block: &mut [u8],
+    ) {
+        // Convert coefficients from a MCU row to samples.
+        let ComponentMetadata {
+            block_count,
+            line_stride,
+            block_width,
+            dct_scale,
+        } = metadata;
+
+        assert_eq!(data.len(), block_count * 64);
+
+        let mut output_buffer = [0; 64];
+        for i in 0..block_count {
+            let x = (i % block_width) * dct_scale;
+            let y = (i / block_width) * dct_scale;
+
+            let coefficients: &[i16; 64] = &data[i * 64..(i + 1) * 64].try_into().unwrap();
+
+            // Write to a temporary intermediate buffer, a 8x8 'image'.
+            dequantize_and_idct_block(
+                dct_scale,
+                coefficients,
+                &*quantization_table,
+                8,
+                &mut output_buffer,
+            );
+
+            let write_back = &mut result_block[y * line_stride + x..];
+
+            let buffered_lines = output_buffer.chunks_mut(8);
+            let back_lines = write_back.chunks_mut(line_stride);
+
+            for (buf, back) in buffered_lines.zip(back_lines).take(dct_scale) {
+                back[..dct_scale].copy_from_slice(&buf[..dct_scale]);
+            }
+        }
+    }
+}
+
+impl Worker for Scoped {
+    fn start(&mut self, row_data: RowData) -> Result<()> {
+        self.inner.start_immediate(row_data);
+        Ok(())
+    }
+
+    fn append_row(&mut self, row: (usize, Vec<i16>)) -> Result<()> {
+        let inner = &mut self.inner;
+        let (index, data) = row;
+
+        let quantization_table = inner.quantization_tables[index].as_ref().unwrap().clone();
+        let metadata = inner.component_metadata(index).unwrap();
+        let result_block = &mut inner.results[index][inner.offsets[index]..];
+        inner.offsets[index] += metadata.bytes_used();
+
+        ImmediateWorker::append_row_locked(quantization_table, metadata, data, result_block);
+        Ok(())
+    }
+
+    fn get_result(&mut self, index: usize) -> Result<Vec<u8>> {
+        let result = self.inner.get_result_immediate(index);
+        Ok(result)
+    }
+
+    // Magic sauce, these _may_ run in parallel.
+    fn append_rows(&mut self, iter: &mut dyn Iterator<Item = (usize, Vec<i16>)>) -> Result<()> {
+        let inner = &mut self.inner;
+        rayon::in_place_scope(|scope| {
+            let metadatas = [
+                inner.component_metadata(0),
+                inner.component_metadata(1),
+                inner.component_metadata(2),
+                inner.component_metadata(3),
+            ];
+
+            let [res0, res1, res2, res3] = &mut inner.results;
+
+            // Lazily get the blocks. Note: if we've already collected results from a component
+            // then the result vector has already been deallocated/taken. But no more tasks should
+            // be created for it.
+            let mut result_blocks = [
+                res0.get_mut(inner.offsets[0]..).unwrap_or(&mut []),
+                res1.get_mut(inner.offsets[1]..).unwrap_or(&mut []),
+                res2.get_mut(inner.offsets[2]..).unwrap_or(&mut []),
+                res3.get_mut(inner.offsets[3]..).unwrap_or(&mut []),
+            ];
+
+            // First we schedule everything, making sure their index is right etc.
+            for (index, data) in iter {
+                let metadata = metadatas[index].unwrap();
+                let quantization_table = inner.quantization_tables[index].as_ref().unwrap().clone();
+
+                inner.offsets[index] += metadata.bytes_used();
+                let (result_block, tail) =
+                    core::mem::take(&mut result_blocks[index]).split_at_mut(metadata.bytes_used());
+                result_blocks[index] = tail;
+
+                scope.spawn(move |_| {
+                    ImmediateWorker::append_row_locked(
+                        quantization_table,
+                        metadata,
+                        data,
+                        result_block,
+                    )
+                });
+            }
+        });
+
+        Ok(())
+    }
+}
+
+impl ComponentMetadata {
+    fn bytes_used(&self) -> usize {
+        self.block_count * self.dct_scale * self.dct_scale
+    }
+}
+
+pub fn compute_image_parallel(
+    components: &[Component],
+    data: Vec<Vec<u8>>,
+    output_size: Dimensions,
+    color_transform: ColorTransform,
+) -> Result<Vec<u8>> {
+    let color_convert_func = choose_color_convert_func(components.len(), color_transform)?;
+    let upsampler = Upsampler::new(components, output_size.width, output_size.height)?;
+    let line_size = output_size.width as usize * components.len();
+    let mut image = vec![0u8; line_size * output_size.height as usize];
+
+    image
+        .par_chunks_mut(line_size)
+        .with_max_len(1)
+        .enumerate()
+        .for_each(|(row, line)| {
+            upsampler.upsample_and_interleave_row(
+                &data,
+                row,
+                output_size.width as usize,
+                line,
+                color_convert_func,
+            );
+        });
+
+    Ok(image)
+}