Benchmark Rust against pinned C# reference (#105)

crates/libremetaverse/src/targa.rs

@@ -11,6 +11,16 @@ type TgaPalette = (usize, Vec<[u8; 4]>);
 pub struct Targa;
 
 impl Targa {
+    /// Decodes an in-memory TGA or DDS payload without copying it through the
+    /// compatibility stream boundary.
+    ///
+    /// # Errors
+    ///
+    /// Returns a typed error for oversized, malformed, or unsupported input.
+    pub fn decode_to_managed_image_with_bytes(data: &[u8]) -> Result<ManagedImage, Error> {
+        decode(data)
+    }
+
     /// Decodes a TGA or DDS file into planar managed-image storage.
     ///
     /// # Errors
@@ -185,6 +195,15 @@ fn decode_tga(bytes: &[u8]) -> Result<ManagedImage, Error> {
         return Err(parse(18, "truncated TGA image ID"));
     }
     let palette = read_tga_palette(bytes, header, has_color_map, color_mapped, &mut position)?;
+    if !rle
+        && !grayscale
+        && palette.is_none()
+        && matches!(depth, 24 | 32)
+        && header[17] & 0x30 == 0x20
+    {
+        decode_plain_truecolor(bytes, position, pixels, pixel_bytes, depth, &mut image)?;
+        return Ok(image);
+    }
     let mut decoded = 0;
     while decoded < pixels {
         let (count, repeated) = if rle {
@@ -238,6 +257,30 @@ fn decode_tga(bytes: &[u8]) -> Result<ManagedImage, Error> {
     Ok(image)
 }
 
+fn decode_plain_truecolor(
+    bytes: &[u8],
+    position: usize,
+    pixels: usize,
+    pixel_bytes: usize,
+    depth: u8,
+    image: &mut ManagedImage,
+) -> Result<(), Error> {
+    let byte_length = pixels.checked_mul(pixel_bytes).ok_or(Error::Argument)?;
+    let end = position.checked_add(byte_length).ok_or(Error::Argument)?;
+    let data = bytes
+        .get(position..end)
+        .ok_or_else(|| parse(position, "truncated TGA pixel data"))?;
+    for (target, pixel) in data.chunks_exact(pixel_bytes).enumerate() {
+        image.blue[target] = pixel[0];
+        image.green[target] = pixel[1];
+        image.red[target] = pixel[2];
+        if depth == 32 {
+            image.alpha[target] = pixel[3];
+        }
+    }
+    Ok(())
+}
+
 fn tga_channels(
     grayscale: bool,
     color_mapped: bool,