Optimize match_len == 3 (#146)

* Add throughput to benches

* Trim debug/error fmt

* Amortize bounds checks in apply_match fast path

* Avoid panic in tree_lookup

benches/bench.rs

@@ -50,6 +50,7 @@ macro_rules! decompress_bench {
             let compressed = compress_to_vec(input.as_slice(), $level);
 
             let mut out_len: usize = 0;
+            b.bytes = input.len() as _;
             b.iter(|| unsafe {
                 w($decompress_func(
                     compressed.as_ptr() as *mut c_void,
@@ -70,6 +71,7 @@ macro_rules! compress_bench {
 
             let mut out_len: usize = 0;
             let flags = create_comp_flags_from_zip_params($level, -15, 0) as i32;
+            b.bytes = input.len() as _;
             b.iter(|| unsafe {
                 w($compress_func(
                     input.as_ptr() as *mut c_void,

miniz_oxide/src/inflate/core.rs

@@ -2,6 +2,7 @@
 
 use super::*;
 use crate::shared::{update_adler32, HUFFMAN_LENGTH_ORDER};
+use ::core::cell::Cell;
 
 use ::core::convert::TryInto;
 use ::core::{cmp, slice};
@@ -52,7 +53,12 @@ impl HuffmanTable {
         loop {
             // symbol here indicates the position of the left (0) node, if the next bit is 1
             // we add 1 to the lookup position to get the right node.
-            symbol = i32::from(self.tree[(!symbol + ((bit_buf >> code_len) & 1) as i32) as usize]);
+            let tree_index = (!symbol + ((bit_buf >> code_len) & 1) as i32) as usize;
+            debug_assert!(tree_index < self.tree.len());
+            if tree_index >= self.tree.len() {
+                break;
+            }
+            symbol = i32::from(self.tree[tree_index]);
             code_len += 1;
             if symbol >= 0 {
                 break;
@@ -896,15 +902,27 @@ fn apply_match(
     match_len: usize,
     out_buf_size_mask: usize,
 ) {
-    debug_assert!(out_pos + match_len <= out_slice.len());
+    debug_assert!(out_pos.checked_add(match_len).unwrap() <= out_slice.len());
 
     let source_pos = out_pos.wrapping_sub(dist) & out_buf_size_mask;
 
     if match_len == 3 {
-        // Fast path for match len 3.
-        out_slice[out_pos] = out_slice[source_pos];
-        out_slice[out_pos + 1] = out_slice[(source_pos + 1) & out_buf_size_mask];
-        out_slice[out_pos + 2] = out_slice[(source_pos + 2) & out_buf_size_mask];
+        let out_slice = Cell::from_mut(out_slice).as_slice_of_cells();
+        if let Some(dst) = out_slice.get(out_pos..out_pos + 3) {
+            // Moving bounds checks before any memory mutation allows the optimizer
+            // combine them together.
+            let src = out_slice
+                .get(source_pos)
+                .zip(out_slice.get((source_pos + 1) & out_buf_size_mask))
+                .zip(out_slice.get((source_pos + 2) & out_buf_size_mask));
+            if let Some(((a, b), c)) = src {
+                // For correctness, the memory reads and writes have to be interleaved.
+                // Cells make it possible for read and write references to overlap.
+                dst[0].set(a.get());
+                dst[1].set(b.get());
+                dst[2].set(c.get());
+            }
+        }
         return;
     }
 

miniz_oxide/src/inflate/mod.rs

@@ -90,13 +90,14 @@ pub struct DecompressError {
 
 #[cfg(feature = "with-alloc")]
 impl alloc::fmt::Display for DecompressError {
+    #[cold]
     fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>) -> ::core::fmt::Result {
         f.write_str(match self.status {
             TINFLStatus::FailedCannotMakeProgress => "Truncated input stream",
             TINFLStatus::BadParam => "Invalid output buffer size",
             TINFLStatus::Adler32Mismatch => "Adler32 checksum mismatch",
             TINFLStatus::Failed => "Invalid input data",
-            TINFLStatus::Done => unreachable!(),
+            TINFLStatus::Done => "", // Unreachable
             TINFLStatus::NeedsMoreInput => "Truncated input stream",
             TINFLStatus::HasMoreOutput => "Output size exceeded the specified limit",
         })

src/lib_oxide.rs

@@ -24,12 +24,13 @@ pub enum InternalState {
 }
 
 impl fmt::Debug for InternalState {
+    #[cold]
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let name = match &self {
             InternalState::Inflate(_) => "Decompressor",
             InternalState::Deflate(_) => "Compressor",
         };
-        write!(f, "{}", name)
+        f.write_str(name)
     }
 }