initial huffman; DRY main

src/compression_scheme.rs

@@ -9,7 +9,7 @@ pub trait CompressionScheme {
 
     /// Encode some bytes into `buf`, returning a [`Header`][Self::Header].
     ///
-    /// This does not necessarily have to be deterministic,
+    /// This does not have to be deterministic,
     /// but it **must** be decodable by [`decode`](Self::decode).
     /// That is, [`decode`](Self::decode) ∘ [`encode`](Self::encode) = `id`.
     fn encode(src: &[u8], buf: &mut BitVec) -> Self::Header;

src/huffman.rs

@@ -0,0 +1,158 @@
+use std::{
+    collections::{BinaryHeap, HashMap},
+    fmt,
+};
+
+use bitvec::prelude::{BitSlice, BitVec};
+
+use crate::CompressionScheme;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct Huffman;
+
+impl CompressionScheme for Huffman {
+    type Header = Option<Node>;
+
+    fn encode(src: &[u8], buf: &mut BitVec) -> Self::Header {
+        let mut counts = HashMap::new();
+        for byte in src {
+            *counts.entry(*byte).or_default() += 1;
+        }
+
+        let tree = Node::build(&counts)?;
+
+        Some(tree)
+    }
+
+    fn decode(src: &BitSlice, header: &Self::Header, buf: &mut Vec<u8>) {
+        if let Some(node) = header {
+            todo!()
+        }
+    }
+
+    fn header_size(header: &Self::Header) -> usize {
+        header.as_ref().map_or(0, Node::byte_size)
+    }
+}
+
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum Node {
+    Leaf { byte: u8 },
+    Branch { left: Box<Self>, right: Box<Self> },
+}
+
+impl Node {
+    fn build(counts: &HashMap<u8, u32>) -> Option<Self> {
+        WeightedNode::build(counts).map(WeightedNode::unburden)
+    }
+
+    /// Write to `buf` the sequence of bits that this tree has assigned `byte`.
+    ///
+    /// # Panics
+    /// Panics if called with a byte that was not passed to [`build`].
+    fn encode_byte(&self, byte: u8, buf: &mut BitVec) {
+        let mut current = self;
+        todo!()
+    }
+
+    /// Return the next encoded byte in the stream of bits.
+    fn decode_byte(src: &BitSlice) -> Option<u8> {
+        todo!()
+    }
+
+    fn byte_size(&self) -> usize {
+        match self {
+            Node::Leaf { .. } => 1,
+            Node::Branch { left, right, .. } => 1 + left.byte_size() + right.byte_size(),
+        }
+    }
+
+    fn write_depth(&self, f: &mut fmt::Formatter<'_>, depth: usize) -> fmt::Result {
+        for _ in 0..depth {
+            write!(f, " ")?;
+        }
+        match self {
+            Node::Leaf { byte } => writeln!(f, "| {:?}", *byte as char),
+            Node::Branch { left, right } => {
+                writeln!(f, "{depth}+")?;
+                left.write_depth(f, depth + 1)?;
+                right.write_depth(f, depth + 1)
+            }
+        }
+    }
+}
+
+impl fmt::Debug for Node {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.write_depth(f, 0)
+    }
+}
+
+#[derive(Clone, PartialEq, Eq)]
+enum WeightedNode {
+    Leaf {
+        byte: u8,
+        count: u32,
+    },
+    Branch {
+        count: u32,
+        left: Box<Self>,
+        right: Box<Self>,
+    },
+}
+
+impl WeightedNode {
+    fn build(counts: &HashMap<u8, u32>) -> Option<Self> {
+        let mut queue = BinaryHeap::new();
+
+        for (&byte, &count) in counts {
+            queue.push(WeightedNode::Leaf { byte, count });
+        }
+
+        loop {
+            let first = queue.pop()?;
+
+            let Some(second) = queue.pop() else {
+                return Some(first);
+            };
+
+            queue.push(WeightedNode::join(first, second));
+        }
+    }
+
+    fn count(&self) -> u32 {
+        match self {
+            Self::Branch { count, .. } | Self::Leaf { count, .. } => *count,
+        }
+    }
+
+    fn join(left: Self, right: Self) -> Self {
+        Self::Branch {
+            count: left.count() + right.count(),
+            left: Box::new(left),
+            right: Box::new(right),
+        }
+    }
+
+    fn unburden(self) -> Node {
+        match self {
+            WeightedNode::Leaf { byte, .. } => Node::Leaf { byte },
+            WeightedNode::Branch { left, right, .. } => Node::Branch {
+                left: Box::new(left.unburden()),
+                right: Box::new(right.unburden()),
+            },
+        }
+    }
+}
+
+impl PartialOrd for WeightedNode {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for WeightedNode {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.count().cmp(&other.count()).reverse()
+    }
+}

src/main.rs

@@ -1,7 +1,12 @@
-use std::io::{self, Read};
+use std::{
+    env,
+    fmt::Debug,
+    io::{self, Read},
+};
 
 mod compression_scheme;
 mod freq;
+mod huffman;
 mod rle;
 #[cfg(test)]
 mod test;
@@ -9,9 +14,12 @@ mod test;
 use bitvec::vec::BitVec;
 pub use compression_scheme::CompressionScheme;
 pub use freq::Freq;
+pub use huffman::Huffman;
 pub use rle::Rle;
 
 fn main() -> Result<(), io::Error> {
+    let debug = env::args().any(|arg| arg == "--debug" || arg == "-d");
+
     let mut buf = Vec::new();
     let len_src = io::stdin().read_to_end(&mut buf)?;
 
@@ -19,14 +27,23 @@ fn main() -> Result<(), io::Error> {
 
     let mut bitbuf = BitVec::new();
 
-    let () = Rle::encode(&buf, &mut bitbuf);
-    let len_rle = bitbuf.len().div_ceil(8);
-    println!("   Rle'd: {len_rle}");
-
-    bitbuf.clear();
-    let header = Freq::encode(&buf, &mut bitbuf);
-    let len_freq = Freq::header_size(&header) + bitbuf.len().div_ceil(8);
-    println!("  Freq'd: {len_freq}");
+    run::<Rle, _>(&buf, &mut bitbuf, "rle", debug);
+    run::<Freq, _>(&buf, &mut bitbuf, "freq", debug);
+    run::<Huffman, _>(&buf, &mut bitbuf, "Huffman", debug);
 
     Ok(())
 }
+
+fn run<Scheme, Header>(buf: &[u8], bitbuf: &mut BitVec, name: &str, debug: bool)
+where
+    Scheme: CompressionScheme<Header = Header>,
+    Header: Debug,
+{
+    bitbuf.clear();
+    let header = Scheme::encode(buf, bitbuf);
+    let len_freq = Scheme::header_size(&header) + bitbuf.len().div_ceil(8);
+    println!("{name}'d: {len_freq}");
+    if debug {
+        eprintln!("{name} header: {header:#?}\n");
+    }
+}

src/test.rs

@@ -1,6 +1,6 @@
 use quickcheck_macros::quickcheck;
 
-use crate::{CompressionScheme, Freq, Rle};
+use crate::{CompressionScheme, Freq, Huffman, Rle};
 
 #[allow(clippy::needless_pass_by_value)]
 #[quickcheck]
@@ -13,3 +13,9 @@ fn roundtrip_freq(src: Vec<u8>) -> bool {
 fn roundtrip_rle(src: Vec<u8>) -> bool {
     Rle::idempotent_on(&src)
 }
+
+#[allow(clippy::needless_pass_by_value)]
+#[quickcheck]
+fn roundtrip_huffman(src: Vec<u8>) -> bool {
+    Huffman::idempotent_on(&src)
+}