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<H1> B.2 The Package Interfaces</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> Package Interfaces is the parent of several library
packages that declare types and other entities useful for interfacing
to foreign languages. It also contains some implementation-defined types
that are useful across more than one language (in particular for interfacing
to assembly language). </DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> The library package
Interfaces has the following skeletal declaration: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Examples"><TT><A NAME="I6070"></A><A NAME="I6071"></A><BR>
<B>package</B> Interfaces <B>is</B><BR>
<B>pragma</B> Pure(Interfaces);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> Integer_<I>n</I> <B>is</B> <B>range</B> -2**(<I>n</I>-1) .. 2**(<I>n</I>-1) - 1; --<I>2's complement</I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> Unsigned_<I>n</I> <B>is</B> <B>mod</B> 2**<I>n</I>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> Shift_Left (Value : Unsigned_<I>n</I>; Amount : Natural)<BR>
<B>return</B> Unsigned_<I>n</I>;<BR>
<B>function</B> Shift_Right (Value : Unsigned_<I>n</I>; Amount : Natural)<BR>
<B>return</B> Unsigned_<I>n</I>;<BR>
<B>function</B> Shift_Right_Arithmetic (Value : Unsigned_<I>n</I>; Amount : Natural)<BR>
<B>return</B> Unsigned_<I>n</I>;<BR>
<B>function</B> Rotate_Left (Value : Unsigned_<I>n</I>; Amount : Natural)<BR>
<B>return</B> Unsigned_<I>n</I>;<BR>
<B>function</B> Rotate_Right (Value : Unsigned_<I>n</I>; Amount : Natural)<BR>
<B>return</B> Unsigned_<I>n</I>;<BR>
...<BR>
<B>end</B> Interfaces;</TT></DIV>
<H4 ALIGN=CENTER>Implementation Requirements</H4>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> An implementation
shall provide the following declarations in the visible part of package
Interfaces: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>Signed and modular integer types of <I>n</I> bits, if supported
by the target architecture, for each <I>n</I> that is at least the size
of a storage element and that is a factor of the word size. The names
of these types are of the form Integer_<I>n</I> for the signed types,
and Unsigned_<I>n</I> for the modular types; </LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC><A NAME="I6072"></A><A NAME="I6073"></A>For each such modular
type in Interfaces, shifting and rotating subprograms as specified in
the declaration of Interfaces above. These subprograms are Intrinsic.
They operate on a bit-by-bit basis, using the binary representation of
the value of the operands to yield a binary representation for the result.
The Amount parameter gives the number of bits by which to shift or rotate.
For shifting, zero bits are shifted in, except in the case of Shift_Right_Arithmetic,
where one bits are shifted in if Value is at least half the modulus.
</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>Floating point types corresponding to each floating point
format fully supported by the hardware. </LI></UL>
<H4 ALIGN=CENTER>Implementation Permissions</H4>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Normal"> An implementation may provide implementation-defined
library units that are children of Interfaces, and may add declarations
to the visible part of Interfaces in addition to the ones defined above.
</DIV>
<H4 ALIGN=CENTER>Implementation Advice</H4>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Normal"> For each implementation-defined convention identifier,
there should be a child package of package Interfaces with the corresponding
name. This package should contain any declarations that would be useful
for interfacing to the language (implementation) represented by the convention.
Any declarations useful for interfacing to any language on the given
hardware architecture should be provided directly in Interfaces. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Normal"> An implementation supporting an interface to
C, COBOL, or Fortran should provide the corresponding package or packages
described in the following clauses. </DIV>
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