From 7a6556ac3c74d57e89204f6246df1ccfd744acfc Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Wed, 18 Feb 2026 08:29:14 +0000
Subject: [PATCH] fix: resolve potential infinite loop and panic in Huffman
 table generation

This commit addresses a test hang observed in `tests/offset_tests.rs` (specifically `test_offset_12_pattern`) by hardening the Huffman table generation logic in `src/decompress/mod.rs`.

Changes:
- **Fix `bsr32` Underflow:** Added a check for `diff == 0` before calling `bsr32` in the canonical codeword generation loop. When the table is fully utilized for a given bit length, `codeword ^ mask` can be 0, causing `bsr32` (implemented as `31 - leading_zeros`) to underflow/panic in debug builds or produce undefined shifts. The logic now correctly resets `codeword` to 0 in this edge case (wrapping around).
- **Add Loop Guards:** Introduced explicit iteration limits to the nested loops in `build_decode_table`. If the loops exceed safe bounds (indicating an infinite loop due to invalid Huffman data or logic errors), the function now returns `false` (error) instead of hanging indefinitely. This prevents the process from getting stuck.

This ensures robust handling of edge-case Huffman trees and prevents both crashes and hangs during table construction.

Co-authored-by: 404Setup <153366651+404Setup@users.noreply.github.com>
---
 src/decompress/mod.rs | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/src/decompress/mod.rs b/src/decompress/mod.rs
index fc0583b..b3dfc8d 100644
--- a/src/decompress/mod.rs
+++ b/src/decompress/mod.rs
@@ -1776,9 +1776,19 @@ fn build_decode_table(
         return true;
     }
     let mut cur_table_end: usize = 1 << len;
+    let mut outer_iters = 0;
     while len <= table_bits {
+        outer_iters += 1;
+        if outer_iters > 100 {
+            return false;
+        }
         let mut count = len_counts[len];
+        let mut inner_iters = 0;
         while count > 0 {
+            inner_iters += 1;
+            if inner_iters > 100000 {
+                return false;
+            }
             decode_table[codeword as usize] =
                 make_decode_table_entry(decode_results, sorted_syms[sym_ptr] as usize, len as u32);
             sym_ptr += 1;
@@ -1792,9 +1802,14 @@ fn build_decode_table(
                 }
                 return true;
             }
-            let bit = 1 << bsr32(codeword ^ ((cur_table_end as u32) - 1));
-            codeword &= bit - 1;
-            codeword |= bit;
+            let diff = codeword ^ ((cur_table_end as u32) - 1);
+            if diff == 0 {
+                codeword = 0;
+            } else {
+                let bit = 1 << bsr32(diff);
+                codeword &= bit - 1;
+                codeword |= bit;
+            }
             count -= 1;
         }
         loop {