From c7b08c52826701efef7e5e99acb180e0c78aa572 Mon Sep 17 00:00:00 2001
From: Jeff Lenamon <85593689+lenamonj@users.noreply.github.com>
Date: Mon, 7 Sep 2026 00:03:12 -0400
Subject: [PATCH] Fix index out of bounds under the disallow_large_window_size
 feature

BROTLI_NUM_HISTOGRAM_DISTANCE_SYMBOLS was defined twice: unconditionally 544 in enc/constants.rs and privately in enc/histogram.rs, where only that copy shrank to 520 under disallow_large_window_size. The histogram array took the private value while every bound took the public one, so the encoder indexed one past the end. Keep one feature-aware definition.
---
 src/enc/constants.rs | 3 +++
 src/enc/histogram.rs | 9 +++------
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/enc/constants.rs b/src/enc/constants.rs
index 4e19756b..2453386f 100644
--- a/src/enc/constants.rs
+++ b/src/enc/constants.rs
@@ -104,7 +104,10 @@ static kContextLookup: [u8; 2048] = [
     5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
     5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7,
 ];
+#[cfg(not(feature = "disallow_large_window_size"))]
 pub const BROTLI_NUM_HISTOGRAM_DISTANCE_SYMBOLS: usize = 544;
+#[cfg(feature = "disallow_large_window_size")]
+pub const BROTLI_NUM_HISTOGRAM_DISTANCE_SYMBOLS: usize = 520;
 pub const BROTLI_NUM_LITERAL_SYMBOLS: usize = 256;
 pub const BROTLI_NUM_COMMAND_SYMBOLS: usize = 704;
 pub const BROTLI_WINDOW_GAP: usize = 16;
diff --git a/src/enc/histogram.rs b/src/enc/histogram.rs
index 3825ccbd..30cb03b2 100644
--- a/src/enc/histogram.rs
+++ b/src/enc/histogram.rs
@@ -5,7 +5,9 @@ use super::super::alloc;
 use super::super::alloc::{SliceWrapper, SliceWrapperMut};
 use super::block_split::BlockSplit;
 use super::command::Command;
-use super::constants::{kSigned3BitContextLookup, kUTF8ContextLookup};
+use super::constants::{
+    kSigned3BitContextLookup, kUTF8ContextLookup, BROTLI_NUM_HISTOGRAM_DISTANCE_SYMBOLS,
+};
 use super::util::floatX;
 use super::vectorization::Mem256i;
 
@@ -63,11 +65,6 @@ impl Default for HistogramCommand {
 }
 //#[derive(Clone)] // #derive is broken for arrays > 32
 
-#[cfg(not(feature = "disallow_large_window_size"))]
-const BROTLI_NUM_HISTOGRAM_DISTANCE_SYMBOLS: usize = 544;
-#[cfg(feature = "disallow_large_window_size")]
-const BROTLI_NUM_HISTOGRAM_DISTANCE_SYMBOLS: usize = 520;
-
 pub struct HistogramDistance {
     pub data_: [u32; BROTLI_NUM_HISTOGRAM_DISTANCE_SYMBOLS],
     pub total_count_: usize,