why weights are uint

[qiulinzhang]

        if self.bit_weights is not None:
            self.weight_quantization_default = quantization_mapping[self.qtype](self, self.weight,
                                                                           self.bit_weights, symmetric=True,
                                                                           uint=True, kwargs=kwargs)

I dont understand for a zero-centered weights, why quantize it as uint?