rewrite algorithm to work in-place

1 files changed, 82 insertions, 0 deletions

diff --git a/src/accessor.rs b/src/accessor.rs
new file mode 100644
index 0000000..89f5251
--- /dev/null
+++ b/src/accessor.rs
@@ -0,0 +1,82 @@
+use super::block::Block;
+
+pub struct BlockAccessor<'a> {
+    data: &'a mut [u8],
+    m_uv_len: usize,
+    m_u_len: usize,
+    m_v_len: usize,
+    num_block_pairs: usize,
+}
+
+impl<'a> BlockAccessor<'a> {
+    pub fn new(message: &'a mut [u8]) -> Self {
+        let num_block_pairs = (message.len() - 16 - 16) / 32;
+        let m_uv_len = (message.len() % 32) * 8;
+        Self {
+            data: message,
+            m_uv_len,
+            m_u_len: 128.min(m_uv_len),
+            m_v_len: m_uv_len.saturating_sub(128),
+            num_block_pairs,
+        }
+    }
+
+    pub fn m_uv_len(&self) -> usize {
+        self.m_uv_len
+    }
+
+    fn suffix_start(&self) -> usize {
+        self.num_block_pairs * 32
+    }
+
+    pub fn m_u(&self) -> Block {
+        let start = self.suffix_start();
+        Block::from_slice(&self.data[start..start + self.m_u_len / 8])
+    }
+
+    pub fn set_m_u(&mut self, m_u: Block) {
+        let start = self.suffix_start();
+        self.data[start..start + self.m_u_len / 8].copy_from_slice(&m_u.0[..self.m_u_len / 8]);
+    }
+
+    pub fn m_v(&self) -> Block {
+        let start = self.suffix_start();
+        Block::from_slice(&self.data[start + self.m_u_len / 8..start + self.m_uv_len / 8])
+    }
+
+    pub fn set_m_v(&mut self, m_v: Block) {
+        let start = self.suffix_start();
+        self.data[start + self.m_u_len / 8..start + self.m_uv_len / 8]
+            .copy_from_slice(&m_v.0[..self.m_v_len / 8]);
+    }
+
+    pub fn m_x(&self) -> Block {
+        let start = self.suffix_start() + self.m_uv_len / 8;
+        Block::from_slice(&self.data[start..start + 16])
+    }
+
+    pub fn set_m_x(&mut self, m_x: Block) {
+        let start = self.suffix_start() + self.m_uv_len / 8;
+        self.data[start..start + 16].copy_from_slice(&m_x.0);
+    }
+
+    pub fn m_y(&self) -> Block {
+        let start = self.suffix_start() + self.m_uv_len / 8;
+        Block::from_slice(&self.data[start + 16..start + 32])
+    }
+
+    pub fn set_m_y(&mut self, m_y: Block) {
+        let start = self.suffix_start() + self.m_uv_len / 8;
+        self.data[start + 16..start + 32].copy_from_slice(&m_y.0);
+    }
+
+    pub fn pairs_mut<'b>(
+        &'b mut self,
+    ) -> impl Iterator<Item = (&'b mut [u8; 16], &'b mut [u8; 16])> {
+        let stop = self.suffix_start();
+        self.data[..stop]
+            .chunks_exact_mut(32)
+            .map(move |x| x.split_at_mut(16))
+            .map(move |(x, y)| (x.try_into().unwrap(), y.try_into().unwrap()))
+    }
+}