Feat (quant_tensor): update __truediv__ behaviour to match "standar…

…d fixed point rules" (#769)

* [quant_tensor] Updated `__truediv__` behaviour based on #740

* [quant_tensor] Updated div behaviour to throw RuntimeError when non-zero zero-point operands are used

* Fix: changed other.tensor -> other.value

src/brevitas/quant_tensor/__init__.py

@@ -406,15 +406,16 @@ def __sub__(self, other):
 
     def __truediv__(self, other):
         if isinstance(other, QuantTensor) and self.is_not_none and other.is_not_none:
-            output_tensor = self.value / other.tensor
-            output_scale = self.scale / other.scale
-            output_bit_width = self.bit_width - other.bit_width
+            output_tensor = self.value / other.value  # Note, output tensor not guaranteed to pass self.is_valid()
+            max_int_denominator = 2 ** (other.bit_width - int(other.signed))
+            output_scale = self.scale / (other.scale * max_int_denominator)
+            output_bit_width = self.bit_width + other.bit_width
             output_signed = self.signed or other.signed
             output_training = self.training or other.training
             if self.is_zero_zero_point(self) and self.is_zero_zero_point(other):
                 output_zero_point = self.zero_point * other.zero_point  # Output zero_point is a new, zero-valued tensor
             else:
-                output_zero_point = None  # TODO non-zero zero point
+                raise RuntimeError("Zero-points of div operands are non-zero, not supported.")
             output = QuantTensor(
                 value=output_tensor,
                 scale=output_scale,