Amend single-argument API with const_assert to confirm validity of tr…

…ailing_zeros as log_2
gendx · Aug 11, 2022 · 9223b59 · 9223b59
1 parent 37e09d1
commit 9223b59
Show file tree

Hide file tree

Showing 3 changed files with 24 additions and 15 deletions.
diff --git a/src/decode/lzma.rs b/src/decode/lzma.rs
@@ -1,5 +1,5 @@
 use crate::decode::lzbuffer::{LzBuffer, LzCircularBuffer};
-use crate::decode::rangecoder::{bittree_probs_len, BitTree, LenDecoder, RangeDecoder};
+use crate::decode::rangecoder::{BitTree, LenDecoder, RangeDecoder};
 use crate::decompress::{Options, UnpackedSize};
 use crate::error;
 use crate::util::vec2d::Vec2D;
@@ -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<{ bittree_probs_len::<6>() }>; 4],
-    align_decoder: BitTree<{ bittree_probs_len::<4>() }>,
+    pos_slot_decoder: [BitTree<{ 1 << 6 }>; 4],
+    align_decoder: BitTree<{ 1 << 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
@@ -150,9 +150,17 @@ where
     }
 }
 
-// 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
+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;
+    };
 }
 
 #[derive(Debug, Clone)]
@@ -162,6 +170,7 @@ pub struct BitTree<const PROBS_ARRAY_LEN: usize> {
 
 impl<const PROBS_ARRAY_LEN: usize> BitTree<PROBS_ARRAY_LEN> {
     pub fn new() -> Self {
+        const_assert!(PROBS_ARRAY_LEN: usize => (1 << (PROBS_ARRAY_LEN.trailing_zeros() as usize)) == PROBS_ARRAY_LEN);
         BitTree {
             probs: [0x400; PROBS_ARRAY_LEN],
         }
@@ -190,9 +199,9 @@ impl<const PROBS_ARRAY_LEN: usize> BitTree<PROBS_ARRAY_LEN> {
 pub struct LenDecoder {
     choice: u16,
     choice2: u16,
-    low_coder: [BitTree<{ bittree_probs_len::<3>() }>; 16],
-    mid_coder: [BitTree<{ bittree_probs_len::<3>() }>; 16],
-    high_coder: BitTree<{ bittree_probs_len::<8>() }>,
+    low_coder: [BitTree<{ 1 << 3 }>; 16],
+    mid_coder: [BitTree<{ 1 << 3 }>; 16],
+    high_coder: BitTree<{ 1 << 8 }>,
 }
 
 impl LenDecoder {

diff --git a/src/encode/rangecoder.rs b/src/encode/rangecoder.rs
@@ -276,15 +276,15 @@ mod test {
     #[test]
     fn test_encode_decode_bittree_zeros() {
         seq!(NUM_BITS in 0..16 {
-            encode_decode_bittree::<NUM_BITS, {decode::rangecoder::bittree_probs_len::<NUM_BITS>()}>
+            encode_decode_bittree::<NUM_BITS, {1 << NUM_BITS}>
                 (&[0; 10000]);
         });
     }
 
     #[test]
     fn test_encode_decode_bittree_ones() {
         seq!(NUM_BITS in 0..16 {
-            encode_decode_bittree::<NUM_BITS, {decode::rangecoder::bittree_probs_len::<NUM_BITS>()}>
+            encode_decode_bittree::<NUM_BITS, {1 << NUM_BITS}>
                 (&[(1 << NUM_BITS) - 1; 10000]);
         });
     }
@@ -294,7 +294,7 @@ mod test {
         seq!(NUM_BITS in 0..16 {
             let max = 1 << NUM_BITS;
             let values: Vec<u32> = (0..max).collect();
-            encode_decode_bittree::<NUM_BITS, {decode::rangecoder::bittree_probs_len::<NUM_BITS>()}>
+            encode_decode_bittree::<NUM_BITS, {1 << NUM_BITS}>
                 (&values);
         });
     }
@@ -323,15 +323,15 @@ mod test {
     #[test]
     fn test_encode_decode_reverse_bittree_zeros() {
         seq!(NUM_BITS in 0..16 {
-            encode_decode_reverse_bittree::<NUM_BITS, {decode::rangecoder::bittree_probs_len::<NUM_BITS>()}>
+            encode_decode_reverse_bittree::<NUM_BITS, {1 << NUM_BITS}>
                 (&[0; 10000]);
         });
     }
 
     #[test]
     fn test_encode_decode_reverse_bittree_ones() {
         seq!(NUM_BITS in 0..16 {
-            encode_decode_reverse_bittree::<NUM_BITS, {decode::rangecoder::bittree_probs_len::<NUM_BITS>()}>
+            encode_decode_reverse_bittree::<NUM_BITS, {1 << NUM_BITS}>
                 (&[(1 << NUM_BITS) - 1; 10000]);
         });
     }
@@ -341,7 +341,7 @@ mod test {
         seq!(NUM_BITS in 0..16 {
             let max = 1 << NUM_BITS;
             let values: Vec<u32> = (0..max).collect();
-            encode_decode_reverse_bittree::<NUM_BITS, {decode::rangecoder::bittree_probs_len::<NUM_BITS>()}>
+            encode_decode_reverse_bittree::<NUM_BITS, {1 << NUM_BITS}>
                 (&values);
         });
     }