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<H1> J.3 Reduced Accuracy Subtypes</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">digits_constraint</FONT>
may be used to define a floating point subtype with a new value for its
requested decimal precision, as reflected by its Digits attribute. Similarly,
a <FONT FACE="Arial, Helvetica">delta_constraint</FONT> may be used to
define an ordinary fixed point subtype with a new value for its <I>delta</I>,
as reflected by its Delta attribute. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>1.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>It might be
more direct to make these attributes specifiable via an <FONT FACE="Arial, Helvetica">attribute_definition_clause</FONT>,
and eliminate the syntax for these <FONT FACE="Arial, Helvetica">_constraint</FONT>s.
</FONT></DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">delta_constraint<A NAME="I7328"></A>
::= </FONT><B>delta</B> <I>static_</I><A NAME="I7329"></A><FONT FACE="Arial, Helvetica">expression</FONT> [<A NAME="I7330"></A><FONT FACE="Arial, Helvetica">range_constraint</FONT>]</DIV>
<H4 ALIGN=CENTER>Name Resolution Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal"> <A NAME="I7331"></A>The <FONT FACE="Arial, Helvetica">expression</FONT>
of a <FONT FACE="Arial, Helvetica">delta_constraint</FONT> is expected
to be of any real type. </DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal"> The <FONT FACE="Arial, Helvetica">expression</FONT>
of a <FONT FACE="Arial, Helvetica">delta_constraint</FONT> shall be static.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> For a <FONT FACE="Arial, Helvetica">subtype_indication</FONT>
with a <FONT FACE="Arial, Helvetica">delta_constraint</FONT>, the <FONT FACE="Arial, Helvetica">subtype_mark</FONT>
shall denote an ordinary fixed point subtype.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal"> <A NAME="I7332"></A>For a <FONT FACE="Arial, Helvetica">subtype_indication</FONT>
with a <FONT FACE="Arial, Helvetica">digits_constraint</FONT>, the <FONT FACE="Arial, Helvetica">subtype_mark</FONT>
shall denote either a decimal fixed point subtype or a floating point
subtype (notwithstanding the rule given in <A HREF="AA-3-5-9.html">3.5.9</A>
that only allows a decimal fixed point subtype). </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>We may need
a better way to deal with obsolescent features with rules that contradict
those of the non-obsolescent parts of the standard. </FONT></DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">subtype_indication</FONT>
with a <FONT FACE="Arial, Helvetica">subtype_mark</FONT> that denotes
an ordinary fixed point subtype and a <FONT FACE="Arial, Helvetica">delta_constraint</FONT>
defines an ordinary fixed point subtype with a <I>delta</I> given by
the value of the <FONT FACE="Arial, Helvetica">expression</FONT> of the
<FONT FACE="Arial, Helvetica">delta_constraint</FONT>. If the <FONT FACE="Arial, Helvetica">delta_constraint</FONT>
includes a <FONT FACE="Arial, Helvetica">range_constraint</FONT>, then
the ordinary fixed point subtype is constrained by the <FONT FACE="Arial, Helvetica">range_constraint</FONT>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">subtype_indication</FONT>
with a <FONT FACE="Arial, Helvetica">subtype_mark</FONT> that denotes
a floating point subtype and a <FONT FACE="Arial, Helvetica">digits_constraint</FONT>
defines a floating point subtype with a requested decimal precision (as
reflected by its Digits attribute) given by the value of the <FONT FACE="Arial, Helvetica">expression</FONT>
of the <FONT FACE="Arial, Helvetica">digits_constraint</FONT>. If the
<FONT FACE="Arial, Helvetica">digits_constraint</FONT> includes a <FONT FACE="Arial, Helvetica">range_constraint</FONT>,
then the floating point subtype is constrained by the <FONT FACE="Arial, Helvetica">range_constraint</FONT>.
</DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Normal"> <A NAME="I7333"></A>A <FONT FACE="Arial, Helvetica">delta_constraint</FONT>
is <I>compatible</I> with an ordinary fixed point subtype if the value
of the <FONT FACE="Arial, Helvetica">expression</FONT> is no less than
the <I>delta</I> of the subtype, and the <FONT FACE="Arial, Helvetica">range_constraint</FONT>,
if any, is compatible with the subtype.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Normal"> <A NAME="I7334"></A>A <FONT FACE="Arial, Helvetica">digits_constraint</FONT>
is <I>compatible</I> with a floating point subtype if the value of the
<FONT FACE="Arial, Helvetica">expression</FONT> is no greater than the
requested decimal precision of the subtype, and the <FONT FACE="Arial, Helvetica">range_constraint</FONT>,
if any, is compatible with the subtype.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Normal"> <A NAME="I7335"></A>The elaboration of a <FONT FACE="Arial, Helvetica">delta_constraint</FONT>
consists of the elaboration of the <FONT FACE="Arial, Helvetica">range_constraint</FONT>,
if any. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Reason: </B>A numeric subtype
is considered ``constrained'' only if a range constraint applies to it.
The only effect of a <FONT FACE="Arial, Helvetica">digits_constraint</FONT>
or a <FONT FACE="Arial, Helvetica">delta_constraint</FONT> without a
<FONT FACE="Arial, Helvetica">range_constraint</FONT> is to specify the
value of the corresponding Digits or Delta attribute in the new subtype.
The set of values of the subtype is not ``constrained'' in any way by
such <FONT FACE="Arial, Helvetica">_constraint</FONT>s. </FONT></DIV>
<H4 ALIGN=CENTER>Wording Changes from Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>11.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>In Ada 83, a <FONT FACE="Arial, Helvetica">delta_constraint</FONT>
is called a fixed_point_constraint, and a <FONT FACE="Arial, Helvetica">digits_constraint</FONT>
is called a floating_point_constraint. We have adopted other terms because
<FONT FACE="Arial, Helvetica">digits_constraint</FONT>s apply primarily
to decimal fixed point types now (they apply to floating point types
only as an obsolescent feature). </FONT></DIV>
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