Merge pull request #1536 from rphmeier/nibblevec

add owning NibbleVec

util/src/lib.rs

@@ -145,6 +145,7 @@ pub mod crypto;
 pub mod triehash;
 pub mod trie;
 pub mod nibbleslice;
+pub mod nibblevec;
 mod heapsizeof;
 pub mod squeeze;
 pub mod semantic_version;

util/src/nibblevec.rs

@@ -0,0 +1,130 @@
+//! An owning, nibble-oriented byte vector.
+
+use ::NibbleSlice;
+
+#[derive(PartialEq, Eq, PartialOrd, Ord, Debug)]
+/// Owning, nibble-oriented byte vector. Counterpart to NibbleSlice.
+pub struct NibbleVec {
+	inner: Vec<u8>,
+	len: usize,
+}
+
+impl NibbleVec {
+	/// Make a new NibbleVec
+	pub fn new() -> Self {
+		NibbleVec {
+			inner: Vec::new(),
+			len: 0
+		}
+	}
+
+	/// Make a NibbleVec with capacity for `n` nibbles.
+	pub fn with_capacity(n: usize) -> Self {
+		NibbleVec {
+			inner: Vec::with_capacity((n / 2) + (n % 2)),
+			len: 0
+		}
+	}
+
+	/// Length of the NibbleVec
+	pub fn len(&self) -> usize { self.len }
+
+	/// Capacity of the NibbleVec.
+	pub fn capacity(&self) -> usize { self.inner.capacity() * 2 }
+
+	/// Try to get the nibble at the given offset.
+	pub fn at(&self, idx: usize) -> u8 {
+		if idx % 2 == 0 {
+			self.inner[idx / 2] >> 4
+		} else {
+			self.inner[idx / 2] & 0x0F
+		}
+	}
+
+	/// Push a nibble onto the NibbleVec. Ignores the high 4 bits.
+	pub fn push(&mut self, nibble: u8) {
+		let nibble = nibble & 0x0F;
+
+		if self.len % 2 == 0 {
+			self.inner.push(nibble << 4);
+		} else {
+			*self.inner.last_mut().expect("len != 0 since len % 2 != 0; inner has a last element; qed") |= nibble;
+		}
+
+		self.len += 1;
+	}
+
+	/// Try to pop a nibble off the NibbleVec. Fails if len == 0.
+	pub fn pop(&mut self) -> Option<u8> {
+		if self.len == 0 {
+			return None;
+		}
+
+		let byte = self.inner.pop().expect("len != 0; inner has last elem; qed");
+		let nibble = if self.len % 2 == 0 {
+			self.inner.push(byte & 0xF0);
+			byte & 0x0F
+		} else {
+			byte >> 4
+		};
+
+		self.len -= 1;
+		Some(nibble)
+	}
+
+	/// Try to treat this NibbleVec as a NibbleSlice. Works only if len is even.
+	pub fn as_nibbleslice(&self) -> Option<NibbleSlice> {
+		if self.len % 2 == 0 {
+			Some(NibbleSlice::new(self.inner()))
+		} else {
+			None
+		}
+	}
+
+	/// Get the underlying byte slice.
+	pub fn inner(&self) -> &[u8] {
+		&self.inner[..]
+	}
+}
+
+impl<'a> From<NibbleSlice<'a>> for NibbleVec {
+	fn from(s: NibbleSlice<'a>) -> Self {
+		let mut v = NibbleVec::with_capacity(s.len());
+		for i in 0..s.len() {
+			v.push(s.at(i));
+		}
+		v
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::NibbleVec;
+
+	#[test]
+	fn push_pop() {
+		let mut v = NibbleVec::new();
+
+		for i in 0..16 {
+			v.push(i);
+			assert_eq!(v.len() - 1, i as usize);
+			assert_eq!(v.at(i as usize), i);
+		}
+
+		for i in (0..16).rev() {
+			assert_eq!(v.pop(), Some(i));
+			assert_eq!(v.len(), i as usize);
+		}
+	}
+
+	#[test]
+	fn nibbleslice_conv() {
+		let mut v = NibbleVec::new();
+		for i in 0..10 {
+			v.push(i);
+		}
+
+		let v2: NibbleVec = v.as_nibbleslice().unwrap().into();
+		assert_eq!(v, v2);
+	}
+}