Simplifies the boolean-bitfield implementation to use bit-vec crate

beacon_chain/types/src/attestation_record.rs

@@ -31,7 +31,7 @@ impl Encodable for AttestationRecord {
         s.append(&self.shard_id);
         s.append_vec(&self.oblique_parent_hashes);
         s.append(&self.shard_block_hash);
-        s.append_vec(&self.attester_bitfield.to_be_vec());
+        s.append_vec(&self.attester_bitfield.to_bytes());
         s.append(&self.justified_slot);
         s.append(&self.justified_block_hash);
         s.append_vec(&self.aggregate_sig.as_bytes());

beacon_chain/utils/boolean-bitfield/Cargo.toml

@@ -5,3 +5,7 @@ authors = ["Paul Hauner <paul@paulhauner.com>"]
 
 [dependencies]
 ssz = { path = "../ssz" }
+bit-vec = "0.5.0"
+
+[dev-dependencies]
+rand = "0.5.5"

beacon_chain/utils/boolean-bitfield/README.md

@@ -1,7 +1,3 @@
 # Boolean Bitfield
 
-A work-in-progress implementation of an unbounded boolean bitfield.
+Implements a set of boolean as a tightly-packed vector of bits.
-
-Based upon a `Vec<u8>`
-
-Documentation TBC...

beacon_chain/utils/boolean-bitfield/src/lib.rs

@@ -1,161 +1,74 @@
-/*
+extern crate bit_vec;
- * Implemenation of a bitfield as a vec. Only
- * supports bytes (Vec<u8>) as the underlying
- * storage.
- *
- * A future implementation should be more efficient,
- * this is just to get the job done for now.
- */
 extern crate ssz;
 
-use std::cmp::max;
+#[cfg(test)]
+extern crate rand;
 
-#[derive(Eq, Clone, Default, Debug)]
+use bit_vec::BitVec;
-pub struct BooleanBitfield {
+
-    len: usize,
+/// A BooleanBitfield represents a set of booleans compactly stored as a vector of bits.
-    vec: Vec<u8>,
+#[derive(Debug, Clone, PartialEq)]
+pub struct BooleanBitfield(BitVec);
+
+/// Error represents some reason a request against a bitfield was not satisfied
+#[derive(Debug)]
+pub enum Error {
+    /// OutOfBounds refers to indexing into a bitfield where no bits exist; returns the illegal index and the current size of the bitfield, respectively
+    OutOfBounds(usize, usize),
 }
 
 impl BooleanBitfield {
     /// Create a new bitfield with a length of zero.
     pub fn new() -> Self {
-        Self {
+        Self { 0: BitVec::new() }
-            len: 0,
-            vec: vec![0],
-        }
     }
 
-    /// Create a new bitfield of a certain capacity
+    /// Create a new bitfield using the supplied `bytes` as input
-    pub fn with_capacity(capacity: usize) -> Self {
+    pub fn from_bytes(bytes: &[u8]) -> Self {
-        let mut vec = Vec::with_capacity(capacity / 8 + 1);
+        Self {
-        vec.push(0);
+            0: BitVec::from_bytes(bytes),
-        Self { len: 0, vec }
+        }
     }
 
     /// Read the value of a bit.
     ///
-    /// Will return `true` if the bit has been set to `true`
+    /// If the index is in bounds, then result is Ok(value) where value is `true` if the bit is 1 and `false` if the bit is 0.
-    /// without then being set to `False`.
+    /// If the index is out of bounds, we return an error to that extent.
-    pub fn get_bit(&self, i: usize) -> bool {
+    pub fn get(&self, i: usize) -> Result<bool, Error> {
-        let bit = |i: usize| i % 8;
+        match self.0.get(i) {
-        let byte = |i: usize| i / 8;
+            Some(value) => Ok(value),
-
+            None => Err(Error::OutOfBounds(i, self.0.len())),
-        if byte(i) >= self.vec.len() {
-            false
-        } else {
-            self.vec[byte(i)] & (1 << (bit(i) as u8)) != 0
         }
     }
 
     /// Set the value of a bit.
     ///
-    /// If this bit is larger than the length of the underlying byte
+    /// Returns the previous value if successful.
-    /// array it will be extended.
+    /// If the index is out of bounds, we return an error to that extent.
-    pub fn set_bit(&mut self, i: usize, to: bool) {
+    pub fn set(&mut self, i: usize, value: bool) -> Result<bool, Error> {
-        let bit = |i: usize| i % 8;
+        let previous = self.get(i)?;
-        let byte = |i: usize| i / 8;
+        self.0.set(i, value);
-
+        Ok(previous)
-        self.len = max(self.len, i + 1);
-
-        if byte(i) >= self.vec.len() {
-            self.vec.resize(byte(i) + 1, 0);
-        }
-        if to {
-            self.vec[byte(i)] = self.vec[byte(i)] | (1 << (bit(i) as u8))
-        } else {
-            self.vec[byte(i)] = self.vec[byte(i)] & !(1 << (bit(i) as u8))
-        }
     }
 
-    /// Return the "length" of this bitfield. Length is defined as
+    /// Returns the index of the highest set bit. Some(n) if some bit is set, None otherwise.
-    /// the highest bit that has been set.
+    pub fn highest_set_bit(&self) -> Option<usize> {
-    ///
+        self.0.iter().rposition(|bit| bit)
-    /// Note: this is distinct from the length of the underlying
+    }
-    /// vector.
+
+    /// Returns the number of bits in this bitfield.
     pub fn len(&self) -> usize {
-        self.len
+        self.0.len()
     }
 
-    /// True if no bits have ever been set. A bit that is set and then
+    /// Returns the number of `1` bits in the bitfield
-    /// unset will still count to the length of the bitfield.
+    pub fn num_set_bits(&self) -> usize {
-    ///
+        self.0.iter().filter(|&bit| bit).count()
-    /// Note: this is distinct from the length of the underlying
-    /// vector.
-    pub fn is_empty(&self) -> bool {
-        self.len == 0
     }
 
-    /// The number of bytes required to represent the bitfield.
+    /// Returns a vector of bytes representing the bitfield
-    pub fn num_bytes(&self) -> usize {
+    pub fn to_bytes(&self) -> Vec<u8> {
-        self.vec.len()
+        self.0.to_bytes()
-    }
-
-    /// Iterate through the underlying vector and count the number of
-    /// true bits.
-    pub fn num_true_bits(&self) -> u64 {
-        let mut count: u64 = 0;
-        for byte in &self.vec {
-            for bit in 0..8 {
-                if byte & (1 << (bit as u8)) != 0 {
-                    count += 1;
-                }
-            }
-        }
-        count
-    }
-
-    /// Iterate through the underlying vector and find the highest
-    /// set bit. Useful for instantiating a new instance from
-    /// some set of bytes.
-    pub fn compute_length(bytes: &[u8]) -> usize {
-        for byte in (0..bytes.len()).rev() {
-            for bit in (0..8).rev() {
-                if bytes[byte] & (1 << (bit as u8)) != 0 {
-                    return (byte * 8) + bit + 1;
-                }
-            }
-        }
-        0
-    }
-
-    /// Get the byte at a position, assuming big-endian encoding.
-    pub fn get_byte(&self, n: usize) -> Option<&u8> {
-        self.vec.get(n)
-    }
-
-    /// Clone and return the underlying byte array (`Vec<u8>`).
-    pub fn to_vec(&self) -> Vec<u8> {
-        self.vec.clone()
-    }
-
-    /// Clone and return the underlying byte array (`Vec<u8>`) in big-endinan format.
-    pub fn to_be_vec(&self) -> Vec<u8> {
-        let mut o = self.vec.clone();
-        o.reverse();
-        o
-    }
-}
-
-impl<'a> From<&'a [u8]> for BooleanBitfield {
-    fn from(input: &[u8]) -> Self {
-        let mut vec = input.to_vec();
-        vec.reverse();
-        BooleanBitfield {
-            vec,
-            len: BooleanBitfield::compute_length(input),
-        }
-    }
-}
-
-impl PartialEq for BooleanBitfield {
-    fn eq(&self, other: &BooleanBitfield) -> bool {
-        (self.vec == other.vec) & (self.len == other.len)
-    }
-}
-
-impl ssz::Encodable for BooleanBitfield {
-    fn ssz_append(&self, s: &mut ssz::SszStream) {
-        s.append_vec(&self.to_vec());
     }
 }
 
@@ -165,12 +78,13 @@ impl ssz::Decodable for BooleanBitfield {
         if (ssz::LENGTH_BYTES + len) > bytes.len() {
             return Err(ssz::DecodeError::TooShort);
         }
+
         if len == 0 {
             Ok((BooleanBitfield::new(), index + ssz::LENGTH_BYTES))
         } else {
-            let b = BooleanBitfield::from(&bytes[(index + 4)..(index + len + 4)]);
+            let field = BooleanBitfield::from_bytes(&bytes[(index + 4)..(index + len + 4)]);
             let index = index + ssz::LENGTH_BYTES + len;
-            Ok((b, index))
+            Ok((field, index))
         }
     }
 }
@@ -178,149 +92,77 @@ impl ssz::Decodable for BooleanBitfield {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use ssz::Decodable;
 
     #[test]
-    fn test_new_from_slice() {
+    fn test_empty_bitfield() {
-        let s = [0];
+        let mut field = BooleanBitfield::new();
-        let b = BooleanBitfield::from(&s[..]);
-        assert_eq!(b.len, 0);
 
-        let s = [255];
+        for _ in 0..100 {
-        let b = BooleanBitfield::from(&s[..]);
+            let index: usize = rand::random();
-        assert_eq!(b.len, 8);
+            assert!(field.get(index).is_err());
-
+            assert!(field.set(index, rand::random()).is_err())
-        let s = [0, 1];
-        let b = BooleanBitfield::from(&s[..]);
-        assert_eq!(b.len, 9);
-
-        let s = [31];
-        let b = BooleanBitfield::from(&s[..]);
-        assert_eq!(b.len, 5);
-    }
-
-    #[test]
-    fn test_ssz_encoding() {
-        let mut b = BooleanBitfield::new();
-        b.set_bit(8, true);
-
-        let mut stream = ssz::SszStream::new();
-        stream.append(&b);
-
-        assert_eq!(stream.drain(), vec![0, 0, 0, 2, 0, 1]);
-    }
-
-    /*
-    #[test]
-    fn test_ssz_decoding() {
-        /*
-         * Correct input
-         */
-        let input = vec![0, 0, 0, 2, 0, 1];
-        let (b, i) = BooleanBitfield::ssz_decode(&input, 0).unwrap();
-        assert_eq!(i, 6);
-        assert_eq!(b.num_true_bits(), 1);
-        assert_eq!(b.get_bit(8), true);
-
-        /*
-         * Input too long
-         */
-        let mut input = vec![0, 0, 0, 2, 0, 1];
-        input.push(42);
-        let (b, i) = BooleanBitfield::ssz_decode(&input, 0).unwrap();
-        assert_eq!(i, 6);
-        assert_eq!(b.num_true_bits(), 1);
-        assert_eq!(b.get_bit(8), true);
-
-        /*
-         * Input too short
-         */
-        let input = vec![0, 0, 0, 2, 1];
-        let res = BooleanBitfield::ssz_decode(&input, 0);
-        assert_eq!(res, Err(ssz::DecodeError::TooShort));
-    }
-    */
-
-    #[test]
-    fn test_new_bitfield_len() {
-        let b = BooleanBitfield::new();
-        assert_eq!(b.len(), 0);
-        assert_eq!(b.to_be_vec(), vec![0]);
-
-        let b = BooleanBitfield::with_capacity(100);
-        assert_eq!(b.len(), 0);
-        assert_eq!(b.to_be_vec(), vec![0]);
-    }
-
-    #[test]
-    fn test_bitfield_set() {
-        let mut b = BooleanBitfield::new();
-        b.set_bit(0, false);
-        assert_eq!(b.to_be_vec(), [0]);
-
-        b = BooleanBitfield::new();
-        b.set_bit(7, true);
-        assert_eq!(b.to_be_vec(), [128]);
-        b.set_bit(7, false);
-        assert_eq!(b.to_be_vec(), [0]);
-        assert_eq!(b.len(), 8);
-
-        b = BooleanBitfield::new();
-        b.set_bit(7, true);
-        b.set_bit(0, true);
-        assert_eq!(b.to_be_vec(), [129]);
-        b.set_bit(7, false);
-        assert_eq!(b.to_be_vec(), [1]);
-        assert_eq!(b.len(), 8);
-
-        b = BooleanBitfield::new();
-        b.set_bit(8, true);
-        assert_eq!(b.to_be_vec(), [1, 0]);
-        assert_eq!(b.len(), 9);
-        b.set_bit(8, false);
-        assert_eq!(b.to_be_vec(), [0, 0]);
-        assert_eq!(b.len(), 9);
-
-        b = BooleanBitfield::new();
-        b.set_bit(15, true);
-        assert_eq!(b.to_be_vec(), [128, 0]);
-        b.set_bit(15, false);
-        assert_eq!(b.to_be_vec(), [0, 0]);
-        assert_eq!(b.len(), 16);
-
-        b = BooleanBitfield::new();
-        b.set_bit(8, true);
-        b.set_bit(15, true);
-        assert_eq!(b.to_be_vec(), [129, 0]);
-        b.set_bit(15, false);
-        assert_eq!(b.to_be_vec(), [1, 0]);
-        assert_eq!(b.len(), 16);
-    }
-
-    #[test]
-    fn test_bitfield_get() {
-        let test_nums = vec![0, 8, 15, 42, 1337];
-        for i in test_nums {
-            let mut b = BooleanBitfield::new();
-            assert_eq!(b.get_bit(i), false);
-            b.set_bit(i, true);
-            assert_eq!(b.get_bit(i), true);
-            b.set_bit(i, true);
         }
     }
 
+    const INPUT: &[u8] = &[0b0000_0010, 0b0000_0010];
+
     #[test]
-    fn test_bitfield_num_true_bits() {
+    fn test_get_from_bitfield() {
-        let mut b = BooleanBitfield::new();
+        let field = BooleanBitfield::from_bytes(INPUT);
-        assert_eq!(b.num_true_bits(), 0);
+        let unset = field.get(0).unwrap();
-        b.set_bit(15, true);
+        assert!(!unset);
-        assert_eq!(b.num_true_bits(), 1);
+        let set = field.get(6).unwrap();
-        b.set_bit(15, false);
+        assert!(set);
-        assert_eq!(b.num_true_bits(), 0);
+        let set = field.get(14).unwrap();
-        b.set_bit(0, true);
+        assert!(set);
-        b.set_bit(7, true);
+    }
-        b.set_bit(8, true);
+
-        b.set_bit(1337, true);
+    #[test]
-        assert_eq!(b.num_true_bits(), 4);
+    fn test_set_for_bitfield() {
+        let mut field = BooleanBitfield::from_bytes(INPUT);
+        let previous = field.set(10, true).unwrap();
+        assert!(!previous);
+        let previous = field.get(10).unwrap();
+        assert!(previous);
+        let previous = field.set(6, false).unwrap();
+        assert!(previous);
+        let previous = field.get(6).unwrap();
+        assert!(!previous);
+    }
+
+    #[test]
+    fn test_highest_set_bit() {
+        let field = BooleanBitfield::from_bytes(INPUT);
+        assert_eq!(field.highest_set_bit().unwrap(), 14);
+
+        let field = BooleanBitfield::new();
+        assert_eq!(field.highest_set_bit(), None);
+    }
+
+    #[test]
+    fn test_len() {
+        let field = BooleanBitfield::from_bytes(INPUT);
+        assert_eq!(field.len(), 16);
+
+        let field = BooleanBitfield::new();
+        assert_eq!(field.len(), 0);
+    }
+
+    #[test]
+    fn test_num_set_bits() {
+        let field = BooleanBitfield::from_bytes(INPUT);
+        assert_eq!(field.num_set_bits(), 2);
+
+        let field = BooleanBitfield::new();
+        assert_eq!(field.num_set_bits(), 0);
+    }
+
+    #[test]
+    fn test_to_bytes() {
+        let field = BooleanBitfield::from_bytes(INPUT);
+        assert_eq!(field.to_bytes(), INPUT);
+
+        let field = BooleanBitfield::new();
+        assert_eq!(field.to_bytes(), vec![]);
     }
 }