From 843fa4168af4d0fe6278a5373793d37eb811affb Mon Sep 17 00:00:00 2001
From: ckolivas <kernel@kolivas.org>
Date: Fri, 13 Feb 2026 12:07:24 +1100
Subject: [PATCH] Address undefined warnings from compilers for left shifting
 negative integers in zpaq.

---
 libzpaq/libzpaq.cpp | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libzpaq/libzpaq.cpp b/libzpaq/libzpaq.cpp
index 633c6f1..42d9f58 100644
--- a/libzpaq/libzpaq.cpp
+++ b/libzpaq/libzpaq.cpp
@@ -801,7 +801,11 @@ void Predictor::init() {
         cr.cm.resize(512);
         for (int j=0; j<256; ++j) {
           cr.cm[j*2]=1<<15;
-          cr.cm[j*2+1]=clamp512k(stretch(st.cminit(j)>>8)<<10);
+          // Left shift of negative values is undefined strictly speaking so
+          // cast it back and forth to safely perform left shift and avoid
+          // compiler issues. Original code:
+          // cr.cm[j*2+1]=clamp512k(stretch(st.cminit(j)>>8)<<10);
+          cr.cm[j*2+1]=clamp512k(static_cast<int>(static_cast<unsigned int>(stretch(st.cminit(j) >> 8)) << 10));
         }
         break;
       case SSE: // sizebits j start limit