png: Make bytemuck optional

zune-png/Cargo.toml

@@ -22,7 +22,6 @@ default = ["sse", "std"]
 zune-core = { path = "../zune-core", version = "0.2" }
 log = "0.4.17"
 zune-inflate = { path = "../zune-inflate", version = "0.2", default-features = false, features = ["zlib"] }
-bytemuck = { version = "1.13.1", default-features = false }
 
 [dev-dependencies]
 nanorand = { version = "0.7.0", default-features = false, features = ["wyrand"] } # testing purposes.

zune-png/src/decoder.rs

@@ -27,7 +27,7 @@ use crate::filters::de_filter::{
 use crate::options::default_chunk_handler;
 use crate::utils::{
     add_alpha, convert_be_to_target_endian_u16, expand_bits_to_byte, expand_palette, expand_trns,
-    is_le
+    is_le, convert_u16_to_u8_slice
 };
 
 /// A palette entry.
@@ -777,11 +777,8 @@ impl<T: ZReaderTrait> PngDecoder<T> {
         {
             &mut out_u8
         } else {
-            let (a, b, c) = bytemuck::pod_align_to_mut::<u16, u8>(&mut out_u16);
+            let b = convert_u16_to_u8_slice(&mut out_u16);
 
-            // a and c should be empty since we do not expect slop bytes on either edge
-            assert!(a.is_empty());
-            assert!(c.is_empty());
             assert_eq!(b.len(), new_len * 2); // length should be twice that of u8
             b
         };

zune-png/src/utils.rs

@@ -350,3 +350,14 @@ pub(crate) fn add_alpha(input: &[u8], output: &mut [u8], colorspace: PngColor, d
         (a, b) => panic!("Unknown combination of depth {a:?} and color type for expand alpha {b:?}")
     }
 }
+
+pub fn convert_u16_to_u8_slice(slice: &mut [u16]) -> &mut [u8] {
+    // Converting a u16 slice to a u8 slice is always correct because
+    // the alignment of the target is smaller.
+    unsafe {
+        std::slice::from_raw_parts_mut(
+            slice.as_ptr() as *mut u8,
+            slice.len().checked_mul(2).unwrap(),
+        )
+    }
+}