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<TITLE>TDF Specification, Issue 4.0 </TITLE>
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<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#0000FF" VLINK="#400080" ALINK="#FF0000">
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<H1>TDF Specification, Issue 4.0</H1>
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<H3>January 1998</H3>
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<A HREF="spec4.html"><IMG SRC="../images/next.gif" ALT="next section"></A>
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<IMG SRC="../images/no_prev.gif" ALT="previous section">
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<IMG SRC="../images/no_top.gif" ALT="current document">
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<A HREF="../index.html"><IMG SRC="../images/home.gif" ALT="TenDRA home page">
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</A>
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<A HREF="spec12.html"><IMG SRC="../images/index.gif" ALT="document index"></A>
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<P>
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<HR>
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<DL>
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<DT><A HREF="#intro">Preface</A><DD>
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<DT><A HREF="spec4.html"><B>1</B> - Introduction</A><DD>
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<DT><A HREF="spec5.html"><B>2</B> - Structure of TDF</A><DD>
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<DT><A HREF="spec6.html"><B>3</B> - Describing the Structure</A><DD>
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<DT><A HREF="spec7.html"><B>4</B> - Installer Behaviour</A><DD>
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<DT><A HREF="spec8.html"><B>5</B> - Specification of TDF Constructs</A><DD>
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<DT><A HREF="spec9.html"><B>6</B> - Supplementary UNIT</A><DD>
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<DT><A HREF="spec10.html"><B>7</B> - Notes</A><DD>
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<DT><A HREF="spec11.html"><B>8</B> - The bit encoding of TDF</A><DD>
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<DT><A HREF="spec12.html">Index</A><DD>
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</DL>
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<HR>
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<H1><A NAME="intro">Preface</A></H1>
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<P>
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This is Issue 4.0 of the TDF Specification. TDF version 4.0 is not
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bitwise compatible with earlier versions.
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<P>
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<H2>Major changes from Issue 3.1</H2>
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<P>
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A new <CODE>SORT</CODE> for <CODE>STRING</CODE> is introduced having
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the same relationship to <CODE>TDFSTRING</CODE> as <CODE>BOOL</CODE>
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has to <CODE>TDFBOOL</CODE>. This is used in place of <CODE>TDFSTRING</CODE>
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in various 3.1 constructions.
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<P>
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They are also used in modified tag and token definitions and declarations
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to provide extra consistency checks in the use of these tags or tokens,
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and also may be used as names external to the TDF system. For example,
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the signature of <I>make_id_tagdec</I> is now:
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<PRE>
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<I>t_intro</I>: TDFINT
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<I>acc</I>: OPTION(ACCESS)
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<I>signature</I>: OPTION(STRING)
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<I>x</I>: SHAPE
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-> TAGDEC
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</PRE>
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A new <CODE>EXP</CODE> constructor, <I>initial_value</I>, is introduced
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to allow dynamic initialisation of global tags.
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<P>
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These changes arise mainly from requirements of C++, but are clearly
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applicable elsewhere.
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<P>
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Magic numbers are introduced at the start of files containing TDF
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bitstream information.
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<P>
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The version 3.1 constructor <I>set_stack_limit</I> has had to be modified
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in the light of experience with platforms with ABIs which require
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upward-growing stacks or use disjoint frame stacks and alloca stacks.
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<P>
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Various other minor changes have been made to elucidate some rather
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pathological cases, e.g. <I>make_nof</I> must have at least one element.
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Also there are some cosmetic changes to improve consistency, e.g.
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the order of the arguments of <I>token</I> are now consistent with
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<I>token_definition</I>.
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<P>
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<H2>Notes on Revision 1</H2>
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<P>
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This Revision 1 of Issue 4.0 incorporates a number of corrections
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which have arisen where inconsistency or impracticability became evident
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when validating the OSF Research Institute's AVS (ANDF Validation
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Suite). Apart from minor textual corrections, the changes are:
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<UL>
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<LI>Use of installer-defined <CODE>TOKEN</CODE>s for accessing variable
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parameter lists - see the companion document
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<A HREF="register.html">TDF Token Register (Revision 1)</A>.<P>
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<LI>Tolerance of overflow necessary to allow simple implementation
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of complex multiply and divide.<P>
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<LI>Modified constraints on the arguments of <I>shift_left</I>,
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<I>shift_right</I>, <I>rotate_left</I>, <I>rotate_right</I>,
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<I>make_dynamic_callees</I>, <I>make_var_tagdec</I>, <I>make_tokdec</I>,
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<I>make_tokdef</I>, and <I>user_info</I>.<P>
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<LI>Modified constant evaluation constraints with respect to <I>env_size</I>
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and <I>env_offset</I>.<P>
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<LI><I>chain_extern</I> no longer supported.
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</UL>
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<P>
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Changes under consideration but not included in Issue 4.0:
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<UL>
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<LI>Tokenisation of the various LIST constructs.<P>
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<LI>Inclusion of the specification of run-time diagnostic information
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in the main specification. This is currently given as an appendix,
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as it it is less mature than the main specification.<P>
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</UL>
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<P>
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<HR>
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<P><I>Part of the <A HREF="../index.html">TenDRA Web</A>.<BR>Crown
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Copyright © 1998.</I></P>
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</BODY>
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</HTML>
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