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<H1> 13.5.3 Bit Ordering</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> The Bit_Order attribute specifies the interpretation
of the storage place attributes. </DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Normal"> <A NAME="I4273"></A>A bit ordering is a method
of interpreting the meaning of the storage place attributes. <A NAME="I4274"></A><A NAME="I4275"></A><A NAME="I4276"></A>High_Order_First
(known in the vernacular as ``big endian'') means that the first bit
of a storage element (bit 0) is the most significant bit (interpreting
the sequence of bits that represent a component as an unsigned integer
value). <A NAME="I4277"></A><A NAME="I4278"></A><A NAME="I4279"></A>Low_Order_First
(known in the vernacular as ``little endian'') means the opposite: the
first bit is the least significant.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> For every specific
record subtype S, the following attribute is defined: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DL Class="Hanging"><DT> S'Bit_Order<DD Class="Hanging">
<A NAME="I4280"></A><A NAME="I4281"></A>Denotes the bit ordering for
the type of S. The value of this attribute is of type System.Bit_Order.
<A NAME="I4282"></A><A NAME="I4283"></A>Bit_Order may be specified for
specific record types via an <FONT FACE="Arial, Helvetica">attribute_definition_clause</FONT>;
the expression of such a clause shall be static. </DL>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> If Word_Size = Storage_Unit, the default bit ordering
is implementation defined. If Word_Size > Storage_Unit, the default
bit ordering is the same as the ordering of storage elements in a word,
when interpreted as an integer. <A NAME="I4284"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal"> The storage place attributes of a component of
a type are interpreted according to the bit ordering of the type. </DIV>
<H4 ALIGN=CENTER>Implementation Advice</H4>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <A NAME="I4285"></A>The
recommended level of support for the nondefault bit ordering is: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>If Word_Size = Storage_Unit, then the implementation should
support the nondefault bit ordering in addition to the default bit ordering.
</LI></UL>
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