From 3b28cc99776d2045ec055109af070890cf879c2f Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 15 Jul 2026 05:40:49 +0000
Subject: [PATCH] Clarify MSVC target-specific overflow paths

---
 src/util/mpz.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/util/mpz.cpp b/src/util/mpz.cpp
index f26a0f98b4..56b48f145d 100644
--- a/src/util/mpz.cpp
+++ b/src/util/mpz.cpp
@@ -35,13 +35,13 @@ static bool mul_overflows(int64_t a, int64_t b, int64_t & result) {
 #elif defined(__GNUC__)
     return __builtin_mul_overflow(a, b, &result);
 #elif defined(_MSC_VER) && !defined(_M_ARM64) && !defined(_M_ARM64EC)
-    // MSVC _mul128 is available on the non-ARM64 targets that still use this path.
+    // MSVC exposes _mul128 on x64 targets, but not on ARM64/ARM64EC.
     __int64 high;
     result = _mul128(a, b, &high);
     // Overflow if high bits are not the sign extension of result
     return high != (result >> 63);
 #elif defined(_MSC_VER)
-    // Unsigned negation preserves the magnitude of INT64_MIN without signed overflow.
+    // Unsigned negation preserves the magnitude of every negative int64_t, including INT64_MIN.
     uint64_t x = a < 0 ? -static_cast<uint64_t>(a) : static_cast<uint64_t>(a);
     uint64_t y = b < 0 ? -static_cast<uint64_t>(b) : static_cast<uint64_t>(b);
     bool is_neg = (a < 0) != (b < 0);