mirror of
https://github.com/michaelcmartin/Ophis.git
synced 2024-09-10 01:54:25 +00:00
220 lines
3.7 KiB
HTML
220 lines
3.7 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
<HTML
|
||
><HEAD
|
||
><TITLE
|
||
>Functionals</TITLE
|
||
><META
|
||
NAME="GENERATOR"
|
||
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
|
||
REL="HOME"
|
||
TITLE="Programming with Ophis"
|
||
HREF="book1.html"><LINK
|
||
REL="UP"
|
||
TITLE="To HLL and Back"
|
||
HREF="p481.html"><LINK
|
||
REL="PREVIOUS"
|
||
TITLE="Conclusion"
|
||
HREF="x813.html"><LINK
|
||
REL="NEXT"
|
||
TITLE="A quick digression on how subroutines work"
|
||
HREF="x836.html"></HEAD
|
||
><BODY
|
||
CLASS="CHAPTER"
|
||
BGCOLOR="#FFFFFF"
|
||
TEXT="#000000"
|
||
LINK="#0000FF"
|
||
VLINK="#840084"
|
||
ALINK="#0000FF"
|
||
><DIV
|
||
CLASS="NAVHEADER"
|
||
><TABLE
|
||
SUMMARY="Header navigation table"
|
||
WIDTH="100%"
|
||
BORDER="0"
|
||
CELLPADDING="0"
|
||
CELLSPACING="0"
|
||
><TR
|
||
><TH
|
||
COLSPAN="3"
|
||
ALIGN="center"
|
||
>Programming with Ophis</TH
|
||
></TR
|
||
><TR
|
||
><TD
|
||
WIDTH="10%"
|
||
ALIGN="left"
|
||
VALIGN="bottom"
|
||
><A
|
||
HREF="x813.html"
|
||
ACCESSKEY="P"
|
||
><<< Previous</A
|
||
></TD
|
||
><TD
|
||
WIDTH="80%"
|
||
ALIGN="center"
|
||
VALIGN="bottom"
|
||
></TD
|
||
><TD
|
||
WIDTH="10%"
|
||
ALIGN="right"
|
||
VALIGN="bottom"
|
||
><A
|
||
HREF="x836.html"
|
||
ACCESSKEY="N"
|
||
>Next >>></A
|
||
></TD
|
||
></TR
|
||
></TABLE
|
||
><HR
|
||
ALIGN="LEFT"
|
||
WIDTH="100%"></DIV
|
||
><DIV
|
||
CLASS="CHAPTER"
|
||
><H1
|
||
><A
|
||
NAME="AEN816"
|
||
></A
|
||
>Functionals</H1
|
||
><P
|
||
> This essay deals with indirect calls. These are the core of an
|
||
enormous number of high level languages: LISP's closures, C's
|
||
function pointers, C++ and Java's virtual method calls, and some
|
||
implementations of the <TT
|
||
CLASS="LITERAL"
|
||
>switch</TT
|
||
> statement.</P
|
||
><P
|
||
> These techniques vary in complexity, and most will not be
|
||
appropriate for large-scale assembler projects. Of them, however,
|
||
the Data-Directed approach is the most likely to lead to organized
|
||
and maintainable code.</P
|
||
><DIV
|
||
CLASS="SECTION"
|
||
><H1
|
||
CLASS="SECTION"
|
||
><A
|
||
NAME="AEN821"
|
||
>Function Pointers</A
|
||
></H1
|
||
><P
|
||
> Because assembly language is totally untyped, function pointers
|
||
are the same as any other sixteen-bit integer. This makes
|
||
representing them really quite easy; most assemblers should permit
|
||
routines to be declared simply by naming the routine as
|
||
a <TT
|
||
CLASS="LITERAL"
|
||
>.word</TT
|
||
> directly.
|
||
</P
|
||
><P
|
||
> To actually invoke these methods, copy them to some sixteen-bit
|
||
location (say, <TT
|
||
CLASS="LITERAL"
|
||
>target</TT
|
||
>) and then invoking the
|
||
method is a simple matter of the using an indirect jump:
|
||
the <TT
|
||
CLASS="LITERAL"
|
||
>JMP<EFBFBD>(target)</TT
|
||
> instruction.
|
||
</P
|
||
><P
|
||
> There's really only one subtlety here, and it's that the indirect
|
||
jump is an indirect <I
|
||
CLASS="EMPHASIS"
|
||
>jump</I
|
||
>, not an
|
||
indirect <I
|
||
CLASS="EMPHASIS"
|
||
>function call</I
|
||
>. Thus, if some
|
||
function <TT
|
||
CLASS="LITERAL"
|
||
>A</TT
|
||
> makes in indirect jump to some
|
||
routine, when that routine returns, it returns to whoever
|
||
called <TT
|
||
CLASS="LITERAL"
|
||
>A</TT
|
||
>, not <TT
|
||
CLASS="LITERAL"
|
||
>A</TT
|
||
>
|
||
itself.
|
||
</P
|
||
><P
|
||
> There are several ways of dealing with this, but only one correct
|
||
way, which is to structure your procedures so that any call
|
||
to <TT
|
||
CLASS="LITERAL"
|
||
>JMP<EFBFBD>(xxxx)</TT
|
||
> occurs at the very
|
||
end.
|
||
</P
|
||
></DIV
|
||
></DIV
|
||
><DIV
|
||
CLASS="NAVFOOTER"
|
||
><HR
|
||
ALIGN="LEFT"
|
||
WIDTH="100%"><TABLE
|
||
SUMMARY="Footer navigation table"
|
||
WIDTH="100%"
|
||
BORDER="0"
|
||
CELLPADDING="0"
|
||
CELLSPACING="0"
|
||
><TR
|
||
><TD
|
||
WIDTH="33%"
|
||
ALIGN="left"
|
||
VALIGN="top"
|
||
><A
|
||
HREF="x813.html"
|
||
ACCESSKEY="P"
|
||
><<< Previous</A
|
||
></TD
|
||
><TD
|
||
WIDTH="34%"
|
||
ALIGN="center"
|
||
VALIGN="top"
|
||
><A
|
||
HREF="book1.html"
|
||
ACCESSKEY="H"
|
||
>Home</A
|
||
></TD
|
||
><TD
|
||
WIDTH="33%"
|
||
ALIGN="right"
|
||
VALIGN="top"
|
||
><A
|
||
HREF="x836.html"
|
||
ACCESSKEY="N"
|
||
>Next >>></A
|
||
></TD
|
||
></TR
|
||
><TR
|
||
><TD
|
||
WIDTH="33%"
|
||
ALIGN="left"
|
||
VALIGN="top"
|
||
>Conclusion</TD
|
||
><TD
|
||
WIDTH="34%"
|
||
ALIGN="center"
|
||
VALIGN="top"
|
||
><A
|
||
HREF="p481.html"
|
||
ACCESSKEY="U"
|
||
>Up</A
|
||
></TD
|
||
><TD
|
||
WIDTH="33%"
|
||
ALIGN="right"
|
||
VALIGN="top"
|
||
>A quick digression on how subroutines work</TD
|
||
></TR
|
||
></TABLE
|
||
></DIV
|
||
></BODY
|
||
></HTML
|
||
> |