Convert pointers without bytemuck

Author: fjarri

Cargo.lock

@@ -18,7 +18,6 @@ rust-version = "1.85"
 
 [dependencies]
 subtle = { version = "2.6", default-features = false }
-bytemuck = { version = "1.24", default-features = false, features = ["must_cast", "must_cast_extra"] }
 
 # optional dependencies
 der = { version = "0.8.0-rc.9", optional = true, default-features = false }

Cargo.toml

@@ -231,14 +231,6 @@ impl Serialize for Limb {
 #[cfg(feature = "zeroize")]
 impl zeroize::DefaultIsZeroes for Limb {}
 
-// SAFETY: `Limb` is a newtype of an integer POD type
-#[allow(unsafe_code)]
-unsafe impl bytemuck::Zeroable for Limb {}
-
-// SAFETY: `Limb` is a newtype of an integer POD type
-#[allow(unsafe_code)]
-unsafe impl bytemuck::Pod for Limb {}
-
 #[cfg(test)]
 mod tests {
     #[cfg(feature = "alloc")]

src/limb.rs

@@ -223,6 +223,18 @@ impl<const LIMBS: usize> Uint<LIMBS> {
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub struct EncodedUint<const LIMBS: usize>([Word; LIMBS]);
 
+#[allow(unsafe_code)]
+const fn cast_slice(limbs: &[Word]) -> &[u8] {
+    let new_len = size_of_val(limbs);
+    unsafe { core::slice::from_raw_parts(limbs.as_ptr() as *mut u8, new_len) }
+}
+
+#[allow(unsafe_code)]
+const fn cast_slice_mut(limbs: &mut [Word]) -> &mut [u8] {
+    let new_len = size_of_val(limbs);
+    unsafe { core::slice::from_raw_parts_mut(limbs.as_mut_ptr() as *mut u8, new_len) }
+}
+
 impl<const LIMBS: usize> EncodedUint<LIMBS> {
     const fn new_le(value: &Uint<LIMBS>) -> Self {
         let mut buffer = [0; LIMBS];
@@ -233,8 +245,7 @@ impl<const LIMBS: usize> EncodedUint<LIMBS> {
 
             // We could cast the whole `buffer` to bytes at once,
             // but IndexMut does not work in const context.
-            let dst_bytes: &mut [u8] =
-                bytemuck::must_cast_slice_mut(core::slice::from_mut(&mut buffer[i]));
+            let dst_bytes: &mut [u8] = cast_slice_mut(core::slice::from_mut(&mut buffer[i]));
 
             // `copy_from_slice` can be used here when MSRV moves past 1.87
             let mut j = 0;
@@ -257,7 +268,7 @@ impl<const LIMBS: usize> EncodedUint<LIMBS> {
             // We could cast the whole `buffer` to bytes at once,
             // but IndexMut does not work in const context.
             let dst_bytes: &mut [u8] =
-                bytemuck::must_cast_slice_mut(core::slice::from_mut(&mut buffer[LIMBS - 1 - i]));
+                cast_slice_mut(core::slice::from_mut(&mut buffer[LIMBS - 1 - i]));
 
             // `copy_from_slice` can be used here when MSRV moves past 1.87
             let mut j = 0;
@@ -280,13 +291,13 @@ impl<const LIMBS: usize> Default for EncodedUint<LIMBS> {
 
 impl<const LIMBS: usize> AsRef<[u8]> for EncodedUint<LIMBS> {
     fn as_ref(&self) -> &[u8] {
-        bytemuck::must_cast_slice(&self.0)
+        cast_slice(&self.0)
     }
 }
 
 impl<const LIMBS: usize> AsMut<[u8]> for EncodedUint<LIMBS> {
     fn as_mut(&mut self) -> &mut [u8] {
-        bytemuck::must_cast_slice_mut(&mut self.0)
+        cast_slice_mut(&mut self.0)
     }
 }