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<h1>variant</h1>
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<p>The attribute is used to refine the currently specified encoding scheme instead of its replacement.
<p>Currently, two encoding schemes are supported in TITAN: RAW and TEXT.
<p>The RAW coder encodes and decodes TTCN-3 values to/from bitstreams. The TEXT coder can be utilized for text-based protocols.
<p>There are presently twenty-two arguments for the RAW coder specified as follows
<ul>
<li>FIELDLENGTH specifies the length of the encoded type;</li>
<li>COMP specifies how negative integer numbers are encoded ;</li>
<li>ALIGN specifies whether the actual value will be padded from left or right;</li>
<li>BITORDERINFIELD specifies whether the most or the less significant bit will be sent first on the port;</li>
<li>BYTEORDER specifies whether the first or the last byte will be sent first on the port;</li>
<li>BITORDER specifies the sequence of the bits within an octet;</li>
<li>HEXORDER specifies the sequencer of the hexadecimal digits in the encoded data;</li>
<li>FIELDORDER specifies how consecutive fields of a structured type is framed into octets;</li>
<li>EXTENSION_BIT manipulates the bit used in some protocols to code data spanning several octets;</li>
<li>EXTENSION_BIT_GROUP limits the extension bit mechanism to a group of the fields in a record;</li>
<li>PADDING is used when the encoded type shall end at a multiple of padding units;</li>
<li>PREPADDING is used when the encoded type shall start at a multiple of padding units;</li>
<li>PADDING_PATTERN specifies padding pattern used by padding mechanism;</li>
<li>PADDALL means that the padding parameter specified for a whole record or set will be valid for every field of the record/set;</li>
<li>LENGTHTO specifies which fields are considered when calculating the length parameter;</li>
<li>LENGTHINDEX extends the LENGTHTO attribute;</li>
<li>UNIT attribute is used in conjunction with the LENGTHTO or POINTERTO attribute;</li>
<li>POINTERTO specifies to which field a pointer points;</li>
<li>PTROFFSET specifies where the pointed field area starts and the base field of pointer calculating;</li>
<li>TAG identifies specific values in certain fields of the set, record elements or union choices;</li>
<li>CROSSTAG is used when one field of a record specifies the union member of an other field of a record;</li>
<li>PRESENCE indicates the presence of an other optional field within records.</li>
</ul>
<p>The above arguments are described in detail in the Appendix B of the TITAN user documentation.</p>
<p>Related keywords:</p>
<ul>
<li><a href="encode.html"><b><font face="Courier New" color="#003258" size="4">encode</font></b></a></li>
<li><a href="with.html"><b><font face="Courier New" color="#003258" size="4">with</font></b></a></li>
<li><a href="override.html"><b><font face="Courier New" color="#003258" size="4">override</font></b></a></li>
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<h3 align="center"><font face="Courier New" color="#003258" size="5"><b>variant</b></font> [ <font face="Courier New" color="#003258" size="5"><b>override</b></font> ] [ <font
face="Courier New" color="#003258" size="5"><b>(</b></font><i>qualifier</i><font face="Courier New" color="#003258" size="5"><b>)</b></font> ] <font face="Courier New" color="#003258" size="5"><b>"</b></font><i>argument</i><b><font
face="Courier New" color="#003258" size="5">"</font></b></h3>
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<ul>
<li>
<p>the optional <b><font face="Courier New">override</font></b> directive forces all contained types at all lower scopes to be forced to the specified attribute.</p>
</li>
<li>
<p>the optional <i>qualifier</i> points out the entity for which the argument is valid.</p>
</li>
<li>
<p><i>argument</i> is a free-text string specifying the actual attribute.</p>
</li>
<li>When using the variant attribute, it is very important to specify the desired codec in the with attributes of the module definition using the <code>encode</code> directive.
</ul>
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<p>Example:
<p><code> module m {<br>
type integer INT2 with { variant "COMP(2scompl)", "FIELDLENGTH(8)" } </font><br>
} with { encode "RAW" } </code>
<p>The encoding of the integer value -1 results in the bit string 11111111.</p>
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<p><a HREF="BNF.html#attribkeyword">BNF definition</a> of <font face="Courier New"> variant</font></p>
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