Add canonical mod with reference i16-diff encode

Cargo.toml

@@ -19,10 +19,6 @@ exclude = [
 [dev-dependencies]
 png = "^0.17.2"
 
-[features]
-reference-encoder = []
-default = []
-
 [target.'cfg(bench)'.dev-dependencies]
 # to activate, pass RUSTFLAGS="--cfg bench" until cargo does this automatically
 criterion = "^0.3.5"

src/canonical.rs

@@ -0,0 +1,10 @@
+use crate::colorspace::ColorSpace;
+use crate::encode::qoi_encode_to_vec_impl;
+use crate::error::Result;
+
+pub fn qoi_encode_to_vec(
+    data: impl AsRef<[u8]>, width: u32, height: u32, channels: u8,
+    colorspace: impl Into<ColorSpace>,
+) -> Result<Vec<u8>> {
+    qoi_encode_to_vec_impl::<true>(data.as_ref(), width, height, channels, colorspace.into())
+}

src/encode.rs

@@ -46,7 +46,7 @@ impl WriteBuf {
 }
 
 #[inline]
-fn encode_diff_reference<const N: usize>(
+fn encode_diff_canonical<const N: usize>(
     px: Pixel<N>, px_prev: Pixel<N>, buf: &mut WriteBuf,
 ) -> Option<(bool, bool, bool, bool)> {
     let vr = (px.r() as i16) - (px_prev.r() as i16);
@@ -122,7 +122,7 @@ fn encode_diff_wrapping<const N: usize>(
     }
 }
 
-pub(crate) fn qoi_encode_impl<const N: usize>(
+pub(crate) fn qoi_encode_impl<const N: usize, const CANONICAL: bool>(
     data: &[u8], width: u32, height: u32, colorspace: ColorSpace,
 ) -> Result<Vec<u8>>
 where
@@ -190,8 +190,8 @@ where
             } else {
                 *index_px = px;
 
-                let nonzero = if cfg!(feature = "reference-encoder") {
-                    encode_diff_reference::<N>(px, px_prev, &mut buf)
+                let nonzero = if CANONICAL {
+                    encode_diff_canonical::<N>(px, px_prev, &mut buf)
                 } else {
                     encode_diff_wrapping::<N>(px, px_prev, &mut buf)
                 };
@@ -227,15 +227,19 @@ where
     Ok(bytes)
 }
 
+pub(crate) fn qoi_encode_to_vec_impl<const CANONICAL: bool>(
+    data: &[u8], width: u32, height: u32, channels: u8, colorspace: ColorSpace,
+) -> Result<Vec<u8>> {
+    match channels {
+        3 => qoi_encode_impl::<3, CANONICAL>(data, width, height, colorspace),
+        4 => qoi_encode_impl::<4, CANONICAL>(data, width, height, colorspace),
+        _ => Err(Error::InvalidChannels { channels }),
+    }
+}
+
 pub fn qoi_encode_to_vec(
     data: impl AsRef<[u8]>, width: u32, height: u32, channels: u8,
     colorspace: impl Into<ColorSpace>,
 ) -> Result<Vec<u8>> {
-    let data = data.as_ref();
-    let colorspace = colorspace.into();
-    match channels {
-        3 => qoi_encode_impl::<3>(data, width, height, colorspace.into()),
-        4 => qoi_encode_impl::<4>(data, width, height, colorspace.into()),
-        _ => Err(Error::InvalidChannels { channels }),
-    }
+    qoi_encode_to_vec_impl::<false>(data.as_ref(), width, height, channels, colorspace.into())
 }

src/lib.rs

@@ -6,6 +6,8 @@ mod error;
 mod header;
 mod pixel;
 
+pub mod canonical;
+
 pub use crate::colorspace::ColorSpace;
 pub use crate::decode::qoi_decode_to_vec;
 pub use crate::encode::qoi_encode_to_vec;