core: Fix overflow in int::mod_euc when self < 0 && rhs == MIN

Author: Daiki Mizukami

src/libcore/num/mod.rs

@@ -1765,7 +1765,11 @@ assert_eq!((-a).mod_euc(-b), 1);
             pub fn mod_euc(self, rhs: Self) -> Self {
                 let r = self % rhs;
                 if r < 0 {
-                    r + rhs.abs()
+                    if rhs.is_negative() {
+                        r - rhs
+                    } else {
+                        r + rhs
+                    }
                 } else {
                     r
                 }

src/libcore/tests/lib.rs

@@ -15,6 +15,7 @@
 #![feature(core_private_diy_float)]
 #![feature(dec2flt)]
 #![feature(decode_utf8)]
+#![feature(euclidean_division)]
 #![feature(exact_size_is_empty)]
 #![feature(fixed_size_array)]
 #![feature(float_internals)]

src/libcore/tests/num/int_macros.rs

@@ -30,6 +30,11 @@ mod tests {
         num::test_num(10 as $T, 2 as $T);
     }
 
+    #[test]
+    fn test_mod_euc() {
+        assert!((-1 as $T).mod_euc(MIN) == MAX);
+    }
+
     #[test]
     pub fn test_abs() {
         assert!((1 as $T).abs() == 1 as $T);