use bit-shifting and or-ing to cover full range

Author: dhalbert

adafruit_mcp3xxx/analog_in.py

@@ -55,9 +55,10 @@ def __init__(
     @property
     def value(self) -> int:
         """Returns the value of an ADC pin as an integer in the range [0, 65535]."""
-        return int(
-            self._mcp.read(self._pin_setting, is_differential=self.is_differential)
-            * (65535 / 1023)
+        # Initial result is only 10 bits.
+        result = int(self._mcp.read(self._pin_setting, is_differential=self.is_differential))
+        # Stretch to 16 bits and cover full range.
+        return (result << 6) | (result >> 4)
         )
 
     @property