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+<?xml version='1.0' ?> <!-- Mode: Docbook -->
+
+<chapter>
+ <title>Programming Notes</title>
+
+ <sect1>
+ <title>Implementation Specific Notes</title>
+ <para>
+ </para>
+ <sect2>
+ <title>&acl;</title>
+ <para>
+ </para>
+ </sect2>
+ <sect2>
+ <title>&lw;</title>
+ <para>
+ </para>
+ </sect2>
+ <sect2>
+ <title>&cmucl;</title>
+ <para>
+ </para>
+ </sect2>
+ </sect1>
+
+ <sect1>
+ <title>Foreign Object Representation and Access</title>
+ <para> There are two main approaches used to represent foreign
+ objects: an integer that represents an address in memory, and a
+ object that also includes run-time typing. The advantage of
+ run-time typing is the system can dereference pointers and perform
+ array access without those functions requiring a type at the cost
+ of additional overhead to generate and store the run-time
+ typing. The advantage of integer representation, at least for
+ &acl;, is that the compiler can generate inline code to
+ dereference pointers. Further, the overhead of the run-time type
+ information is eliminated. The disadvantage is the program must
+ then supply
+ the type to the functions to dereference objects and array.
+ </para>
+ </sect1>
+
+ <sect1>
+ <title>Optimizing Code Using UFFI</title>
+ <sect2>
+ <title>Background</title>
+ <para>
+ Two implementions have different techniques to optimize
+ (open-code) foreign objects. &acl; can open-code foreign
+ object
+ access if pointers are integers and the type of object is
+ specified in the access function. Thus, &uffi; represents objects
+ in &acl; as integers which don't have type information.
+ </para> <para>
+ &cmucl; works best when keeping objects as typed
+ objects. However, it's compiler can open-code object access when
+ the object type is specified in <function>declare</function>
+ commands and in <varname>:type</varname> specifiers in
+ <function>defstruct</function> and <function>defclass</function>.
+ </para> <para> &lw;, in converse to &acl; and &cmucl; does not do
+ any open coding of object access. &lw;, by default, maintains
+ objects with run-time typing. </para>
+ </sect2>
+ <sect2>
+ <title>Cross-Implementation Optimization</title>
+ <para>
+ To fully optimize across platforms, both explicit type
+ information must be passed to dereferencing of pointers and
+ arrays. Though this optimization only helps with &acl;, &uffi;
+ is designed to require this type information be passed the
+ dereference functions. Second, declarations of type should be
+ made in functions, structures, and classes where foreign
+ objects will be help. This will optimize access for &lw;
+ </para>
+ <para>
+ Here is an example that should both methods being used for
+ maximum cross-implementation optimization:
+ <programlisting>
+(uffi:def-type the-struct-type-def the-struct-type)
+(let ((a-foreign-struct (allocate-foreign-object 'the-struct-type)))
+ (declare 'the-struct-type-def a-foreign-struct)
+ (get-slot-value a-foreign-struct 'the-struct-type 'field-name))
+ </programlisting>
+ </para>
+ </sect2>
+ </sect1>
+
+</chapter>