The way bit fields are accessed in many languages is often similar to the processing in BAR:  loads perform "AND" and "shift" operations after loading from the source word, and stores perform "AND," "shift," and "OR" operations as part of storing to the destination.

However, there is one context in which load and store operations occur differently for bit field structures:  this is when a bit field is dereferenced implicitly in a member function (just variable name mentioned; no member selection or pointer-to-member selection operators are used).

In this case, the value of the implicit global variable “bitposition” influences how load and store operations occur.  The value of “bitposition” instructs the opcodes as to the actual alignment of the bit field structure, which does not need to be aligned on a byte boundary.

During deserialization and serialization critical-step methods, the variable “bitposition” is populated automatically, often making its explicit use unnecessary.  But it is possible to manually manipulate “bitposition” to achieve “unaligned bit field” calculation results outside of the contexts of deserialization and serialization.  Of course, this requires significant knowledge of the data format with which the user is working.

  See also:  [Final expression type result] [L-value status gain and loss]
[Overly complex expressions] [Limitations on pointer usage] [Structure member dereference:  bit scan blocks]