From 83a3365bfd9dc17067de26b3cb4c9af55a34644e Mon Sep 17 00:00:00 2001
From: mlugg <mlugg@mlugg.co.uk>
Date: Sat, 13 Sep 2025 11:31:17 +0100
Subject: [PATCH] std.math.big.int: normalize zero result for small
 multiplications

Resolves: #25221
---
 lib/std/math/big/int.zig | 7 +++----
 test/behavior/enum.zig   | 7 +++++++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/lib/std/math/big/int.zig b/lib/std/math/big/int.zig
index b0380444f4..427f2861b7 100644
--- a/lib/std/math/big/int.zig
+++ b/lib/std/math/big/int.zig
@@ -786,11 +786,10 @@ pub const Mutable = struct {
         assert(rma.limbs.ptr != b.limbs.ptr); // illegal aliasing
 
         if (a.limbs.len == 1 and b.limbs.len == 1) {
-            const ov = @mulWithOverflow(a.limbs[0], b.limbs[0]);
-            rma.limbs[0] = ov[0];
-            if (ov[1] == 0) {
+            rma.limbs[0], const overflow_bit = @mulWithOverflow(a.limbs[0], b.limbs[0]);
+            if (overflow_bit == 0) {
                 rma.len = 1;
-                rma.positive = (a.positive == b.positive);
+                rma.positive = (a.positive == b.positive) or rma.limbs[0] == 0;
                 return;
             }
         }
diff --git a/test/behavior/enum.zig b/test/behavior/enum.zig
index d719a611e6..269fba13ba 100644
--- a/test/behavior/enum.zig
+++ b/test/behavior/enum.zig
@@ -1325,3 +1325,10 @@ test "large enum field values" {
         try expect(@intFromEnum(e) == std.math.maxInt(i128));
     }
 }
+
+test "comptime @enumFromInt with signed arithmetic" {
+    const E = enum(i8) { foo = -1, bar = 0 };
+    const x: E = @enumFromInt(@as(i8, -1) * 0);
+    comptime assert(x == .bar);
+    comptime assert(@intFromEnum(x) == 0);
+}