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obj'Bit, where obj is any object, yields the bit offset within the storage unit (byte) that contains the first bit of storage allocated for the object. The value of this attribute is of the type Universal_Integer, and is always a non-negative number not exceeding the value of System.Storage_Unit.

For an object that is a variable or a constant allocated in a register, the value is zero. (The use of this attribute does not force the allocation of a variable to memory).

For an object that is a formal parameter, this attribute applies to either the matching actual parameter or to a copy of the matching actual parameter.

For an access object the value is zero. Note that obj.all'Bit is subject to an Access_Check for the designated object. Similarly for a record component X.C'Bit is subject to a discriminant check and X(I).Bit and X(I1..I2)'Bit are subject to index checks.

This attribute is designed to be compatible with the DEC Ada 83 definition and implementation of the Bit attribute.