code: function is_negative (x) {
          var isOverflowOrNegative = is_overflow(x) || x[9] < 0;
          var leastSignificantBit = x[0] & 1;
          return ((isOverflowOrNegative ? 1 : 0) ^ leastSignificantBit) & 0xFFFFFFFF;
      }
docs: /* checks if x is "negative", requires reduced input