Alternative API with only a single generic argument for BitTree

gendx · Aug 9, 2022 · 37e09d1 · 37e09d1
1 parent 2587208
commit 37e09d1
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Showing 3 changed files with 13 additions and 26 deletions.
diff --git a/src/decode/lzma.rs b/src/decode/lzma.rs
@@ -167,8 +167,8 @@ pub(crate) struct DecoderState {
  pub(crate) lzma_props: LzmaProperties,
  unpacked_size: Option<u64>,
  literal_probs: Vec2D<u16>,
- pos_slot_decoder: [BitTree<6, { bittree_probs_len::<6>() }>; 4],
- align_decoder: BitTree<4, { bittree_probs_len::<4>() }>,
+ pos_slot_decoder: [BitTree<{ bittree_probs_len::<6>() }>; 4],
+ align_decoder: BitTree<{ bittree_probs_len::<4>() }>,
  pos_decoders: [u16; 115],
  is_match: [u16; 192], // true = LZ, false = literal
  is_rep: [u16; 12],

diff --git a/src/decode/rangecoder.rs b/src/decode/rangecoder.rs
@@ -150,62 +150,49 @@ where
  }
 }
 
-/// macro for compile-time const assertions
-macro_rules! const_assert {
- ($($list:ident : $ty:ty),* => $expr:expr) => {{
- struct Assert<$(const $list: $ty,)*>;
- impl<$(const $list: $ty,)*> Assert<$($list,)*> {
- const OK: u8 = 0 - !($expr) as u8;
- }
- Assert::<$($list,)*>::OK
- }};
- ($expr:expr) => {
- const OK: u8 = 0 - !($expr) as u8;
- };
-}
-
 // const fn helper to parameterize the length of the bittree probability array.
 pub const fn bittree_probs_len<const NUM_BITS: usize>() -> usize {
  1 << NUM_BITS
 }
 
 #[derive(Debug, Clone)]
-pub struct BitTree<const NUM_BITS: usize, const PROBS_ARRAY_LEN: usize> {
+pub struct BitTree<const PROBS_ARRAY_LEN: usize> {
  probs: [u16; PROBS_ARRAY_LEN],
 }
 
-impl<const NUM_BITS: usize, const PROBS_ARRAY_LEN: usize> BitTree<NUM_BITS, PROBS_ARRAY_LEN> {
+impl<const PROBS_ARRAY_LEN: usize> BitTree<PROBS_ARRAY_LEN> {
  pub fn new() -> Self {
- const_assert!(NUM_BITS: usize, PROBS_ARRAY_LEN: usize => PROBS_ARRAY_LEN == bittree_probs_len::<NUM_BITS>());
  BitTree {
  probs: [0x400; PROBS_ARRAY_LEN],
  }
  }
 
+ const NUM_BITS: usize = PROBS_ARRAY_LEN.trailing_zeros() as usize;
+
  pub fn parse<R: io::BufRead>(
  &mut self,
  rangecoder: &mut RangeDecoder<R>,
  update: bool,
  ) -> io::Result<u32> {
- rangecoder.parse_bit_tree(NUM_BITS, &mut self.probs, update)
+ rangecoder.parse_bit_tree(Self::NUM_BITS, &mut self.probs, update)
  }
 
  pub fn parse_reverse<R: io::BufRead>(
  &mut self,
  rangecoder: &mut RangeDecoder<R>,
  update: bool,
  ) -> io::Result<u32> {
- rangecoder.parse_reverse_bit_tree(NUM_BITS, &mut self.probs, 0, update)
+ rangecoder.parse_reverse_bit_tree(Self::NUM_BITS, &mut self.probs, 0, update)
  }
 }
 
 #[derive(Debug)]
 pub struct LenDecoder {
  choice: u16,
  choice2: u16,
- low_coder: [BitTree<3, { bittree_probs_len::<3>() }>; 16],
- mid_coder: [BitTree<3, { bittree_probs_len::<3>() }>; 16],
- high_coder: BitTree<8, { bittree_probs_len::<8>() }>,
+ low_coder: [BitTree<{ bittree_probs_len::<3>() }>; 16],
+ mid_coder: [BitTree<{ bittree_probs_len::<3>() }>; 16],
+ high_coder: BitTree<{ bittree_probs_len::<8>() }>,
 }
 
 impl LenDecoder {

diff --git a/src/encode/rangecoder.rs b/src/encode/rangecoder.rs
@@ -266,7 +266,7 @@ mod test {
 
  let mut bufread = BufReader::new(buf.as_slice());
  let mut decoder = RangeDecoder::new(&mut bufread).unwrap();
- let mut tree = decode::rangecoder::BitTree::<NUM_BITS, PROBS_LEN>::new();
+ let mut tree = decode::rangecoder::BitTree::<PROBS_LEN>::new();
  for &v in values {
  assert_eq!(tree.parse(&mut decoder, true).unwrap(), v);
  }
@@ -313,7 +313,7 @@ mod test {
 
  let mut bufread = BufReader::new(buf.as_slice());
  let mut decoder = RangeDecoder::new(&mut bufread).unwrap();
- let mut tree = decode::rangecoder::BitTree::<NUM_BITS, PROBS_LEN>::new();
+ let mut tree = decode::rangecoder::BitTree::<PROBS_LEN>::new();
  for &v in values {
  assert_eq!(tree.parse_reverse(&mut decoder, true).unwrap(), v);
  }