From c93b32b3e50182a2a0ff5ee776c5fa534102e3e7 Mon Sep 17 00:00:00 2001
From: Jorge Aparicio <japaricious@gmail.com>
Date: Mon, 6 Mar 2017 17:46:11 -0500
Subject: [PATCH] fix debug assertion in divdi3

fixes #148
---
 src/int/sdiv.rs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/int/sdiv.rs b/src/int/sdiv.rs
index 51d9c37..f9fd466 100644
--- a/src/int/sdiv.rs
+++ b/src/int/sdiv.rs
@@ -10,8 +10,12 @@ macro_rules! div {
         pub extern "C" fn $intrinsic(a: $ty, b: $ty) -> $tyret {
             let s_a = a >> (<$ty>::bits() - 1);
             let s_b = b >> (<$ty>::bits() - 1);
-            let a = (a ^ s_a) - s_a;
-            let b = (b ^ s_b) - s_b;
+            // NOTE it's OK to overflow here because of the `as $uty` cast below
+            // This whole operation is computing the absolute value of the inputs
+            // So some overflow will happen when dealing with e.g. `i64::MIN`
+            // where the absolute value is `(-i64::MIN) as u64`
+            let a = (a ^ s_a).wrapping_sub(s_a);
+            let b = (b ^ s_b).wrapping_sub(s_b);
             let s = s_a ^ s_b;
 
             let r = udiv!(a as $uty, b as $uty);