chore: checkpoint before Python removal

vendor/block-buffer/src/sealed.rs

@@ -0,0 +1,67 @@
+use super::{ArrayLength, Block};
+use core::slice;
+
+/// Sealed trait for buffer kinds.
+pub trait Sealed {
+    /// Invariant guaranteed by a buffer kind, i.e. with correct
+    /// buffer code this function always returns true.
+    fn invariant(pos: usize, block_size: usize) -> bool;
+
+    /// Split input data into slice of blocks and tail.
+    fn split_blocks<N: ArrayLength<u8>>(data: &[u8]) -> (&[Block<N>], &[u8]);
+}
+
+impl Sealed for super::Eager {
+    #[inline(always)]
+    fn invariant(pos: usize, block_size: usize) -> bool {
+        pos < block_size
+    }
+
+    #[inline(always)]
+    fn split_blocks<N: ArrayLength<u8>>(data: &[u8]) -> (&[Block<N>], &[u8]) {
+        let nb = data.len() / N::USIZE;
+        let blocks_len = nb * N::USIZE;
+        let tail_len = data.len() - blocks_len;
+        // SAFETY: we guarantee that created slices do not point
+        // outside of `data`
+        unsafe {
+            let blocks_ptr = data.as_ptr() as *const Block<N>;
+            let tail_ptr = data.as_ptr().add(blocks_len);
+            (
+                slice::from_raw_parts(blocks_ptr, nb),
+                slice::from_raw_parts(tail_ptr, tail_len),
+            )
+        }
+    }
+}
+
+impl Sealed for super::Lazy {
+    #[inline(always)]
+    fn invariant(pos: usize, block_size: usize) -> bool {
+        pos <= block_size
+    }
+
+    #[inline(always)]
+    fn split_blocks<N: ArrayLength<u8>>(data: &[u8]) -> (&[Block<N>], &[u8]) {
+        if data.is_empty() {
+            return (&[], &[]);
+        }
+        let (nb, tail_len) = if data.len() % N::USIZE == 0 {
+            (data.len() / N::USIZE - 1, N::USIZE)
+        } else {
+            let nb = data.len() / N::USIZE;
+            (nb, data.len() - nb * N::USIZE)
+        };
+        let blocks_len = nb * N::USIZE;
+        // SAFETY: we guarantee that created slices do not point
+        // outside of `data`
+        unsafe {
+            let blocks_ptr = data.as_ptr() as *const Block<N>;
+            let tail_ptr = data.as_ptr().add(blocks_len);
+            (
+                slice::from_raw_parts(blocks_ptr, nb),
+                slice::from_raw_parts(tail_ptr, tail_len),
+            )
+        }
+    }
+}