From 1edd3b7a930f6e2f2f8656ab8f946a8cc61c9d6f Mon Sep 17 00:00:00 2001
From: Artem Pavlenko <artem@mapnik.org>
Date: Fri, 1 Nov 2019 16:15:05 +0000
Subject: [PATCH] use `& mask` for array bounds clipping (provided array size
 is 2^n)

---
 include/mapnik/text/scrptrun.hpp | 5 ++++-
 src/text/scrptrun.cpp            | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/mapnik/text/scrptrun.hpp b/include/mapnik/text/scrptrun.hpp
index c219a2a0d..7cee74197 100644
--- a/include/mapnik/text/scrptrun.hpp
+++ b/include/mapnik/text/scrptrun.hpp
@@ -24,6 +24,9 @@
 #include <unicode/uscript.h>
 #pragma GCC diagnostic pop
 
+const unsigned int STACK_SIZE = 1 << 7; // 2^n
+const unsigned int STACK_MASK = STACK_SIZE - 1;
+
 struct ScriptRecord
 {
     UChar32 startChar = 0;
@@ -85,7 +88,7 @@ private:
     int32_t scriptEnd;
     UScriptCode scriptCode;
 
-    ParenStackEntry parenStack[128];
+    ParenStackEntry parenStack[STACK_SIZE];
     int32_t parenSP;
 
     static int8_t highBit(int32_t value);
diff --git a/src/text/scrptrun.cpp b/src/text/scrptrun.cpp
index bc16cb811..c2985397d 100644
--- a/src/text/scrptrun.cpp
+++ b/src/text/scrptrun.cpp
@@ -161,7 +161,7 @@ UBool ScriptRun::next()
         // characters above it on the stack will be poped.
         if (pairIndex >= 0) {
             if ((pairIndex & 1) == 0) {
-                parenSP = (++parenSP) % ARRAY_SIZE(parenStack); // avoid out-of-bounds access
+                parenSP = (++parenSP) & STACK_MASK; // avoid out-of-bounds access
                 parenStack[parenSP].pairIndex = pairIndex;
                 parenStack[parenSP].scriptCode  = scriptCode;
             } else if (parenSP >= 0) {