Bugfix nagative-number lshift() bit overflow

src/numeric.c

@@ -821,15 +821,28 @@ static mrb_value
 lshift(mrb_state *mrb, mrb_int val, mrb_int width)
 {
   mrb_assert(width > 0);
-  if ((width > NUMERIC_SHIFT_WIDTH_MAX) ||
-      (val   > (MRB_INT_MAX >> width))) {
+  if (val > 0) {
+    if ((width > NUMERIC_SHIFT_WIDTH_MAX) ||
+        (val   > (MRB_INT_MAX >> width))) {
+      goto bit_overflow;
+    }
+  } else {
+    if ((width > NUMERIC_SHIFT_WIDTH_MAX) ||
+        (val   < (MRB_INT_MIN >> width))) {
+      goto bit_overflow;
+    }
+  }
+
+  return mrb_fixnum_value(val << width);
+
+bit_overflow:
+  {
     mrb_float f = (mrb_float)val;
     while (width--) {
       f *= 2;
     }
     return mrb_float_value(mrb, f);
   }
-  return mrb_fixnum_value(val << width);
 }
 
 static mrb_value

test/t/integer.rb

@@ -150,6 +150,9 @@ assert('Integer#<<', '15.2.8.3.12') do
 
   # Left Shift by 31 is bitShift overflow to SignedInt
   assert_equal 2147483648, 1 << 31
+
+  # -3 Left Shift by 30 is bitShift overflow to SignedInt
+  assert_equal -3221225472, -3 << 30
 end
 
 assert('Integer#>>', '15.2.8.3.13') do