223cc6685e
git-svn-id: svn://svn.compuextreme.de/Viitor/V963/Viitor_cc65@5933 504e572c-2e33-0410-9681-be2bf7408885
197 lines
5.2 KiB
HTML
197 lines
5.2 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<META NAME="GENERATOR" CONTENT="LinuxDoc-Tools 0.9.20">
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<TITLE>cc65 Users Guide: Extensions</TITLE>
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<LINK HREF="cc65-6.html" REL=next>
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<LINK HREF="cc65-4.html" REL=previous>
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<LINK HREF="cc65.html#toc5" REL=contents>
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</HEAD>
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<BODY>
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<A HREF="cc65-6.html">Next</A>
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<A HREF="cc65-4.html">Previous</A>
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<A HREF="cc65.html#toc5">Contents</A>
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<HR>
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<H2><A NAME="s5">5.</A> <A HREF="cc65.html#toc5">Extensions</A></H2>
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<P>This cc65 version has some extensions to the ISO C standard.</P>
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<P>
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<UL>
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<LI> The compiler allows to insert assembler statements into the output
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file. The syntax is
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<BLOCKQUOTE><CODE>
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<PRE>
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asm (<string literal>[, optional parameters]) ;
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</PRE>
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</CODE></BLOCKQUOTE>
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or
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<BLOCKQUOTE><CODE>
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<PRE>
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__asm__ (<string literal>[, optional parameters]) ;
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</PRE>
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</CODE></BLOCKQUOTE>
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The first form is in the user namespace and is disabled if the <CODE>-A</CODE>
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switch is given.
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There is a whole section covering inline assembler statements,
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<A HREF="cc65-9.html#inline-asm">see there</A>.
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</LI>
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<LI> There is a special calling convention named "fastcall".
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The syntax for a function declaration using fastcall is
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<BLOCKQUOTE><CODE>
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<PRE>
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<return type> fastcall <function name> (<parameter list>)
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</PRE>
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</CODE></BLOCKQUOTE>
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or
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<BLOCKQUOTE><CODE>
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<PRE>
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<return type> __fastcall__ <function name> (<parameter list>)
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</PRE>
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</CODE></BLOCKQUOTE>
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An example would be
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<BLOCKQUOTE><CODE>
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<PRE>
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void __fastcall__ f (unsigned char c)
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</PRE>
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</CODE></BLOCKQUOTE>
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The first form of the fastcall keyword is in the user namespace and can
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therefore be disabled with the <CODE>
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<A HREF="cc65-2.html#option--standard">--standard</A></CODE> command line option.
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For functions declared as <CODE>fastcall</CODE>, the rightmost parameter is not
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pushed on the stack but left in the primary register when the function
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is called. This will reduce the cost when calling assembler functions
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significantly, especially when the function itself is rather small.
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</LI>
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<LI> There are two pseudo variables named <CODE>__AX__</CODE> and <CODE>__EAX__</CODE>.
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Both refer to the primary register that is used by the compiler to
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evaluate expressions or return function results. <CODE>__AX__</CODE> is of
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type <CODE>unsigned int</CODE> and <CODE>__EAX__</CODE> of type <CODE>long unsigned int</CODE>
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respectively. The pseudo variables may be used as lvalue and rvalue as
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every other variable. They are most useful together with short
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sequences of assembler code. For example, the macro
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<BLOCKQUOTE><CODE>
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<PRE>
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#define hi(x) \
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(__AX__ = (x), \
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asm ("txa"), \
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asm ("ldx #$00"), \
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__AX__)
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</PRE>
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</CODE></BLOCKQUOTE>
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will give the high byte of any unsigned value.
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</LI>
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<LI> Inside a function, the identifier <CODE>__func__</CODE> gives the name of the
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current function as a string. Outside of functions, <CODE>__func__</CODE> is
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undefined.
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Example:
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<BLOCKQUOTE><CODE>
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<PRE>
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#define PRINT_DEBUG(s) printf ("%s: %s\n", __func__, s);
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</PRE>
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</CODE></BLOCKQUOTE>
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The macro will print the name of the current function plus a given
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string.
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</LI>
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<LI> cc65 allows the initialization of <CODE>void</CODE> variables. This may be
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used to create variable structures that are more compatible with
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interfaces written for assembler languages. Here is an example:
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<BLOCKQUOTE><CODE>
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<PRE>
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void GCmd = { (char)3, (unsigned)0x2000, (unsigned)0x3000 };
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</PRE>
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</CODE></BLOCKQUOTE>
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This will be translated as follows:
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<BLOCKQUOTE><CODE>
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<PRE>
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_GCmd:
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.byte 3
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.word $2000
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.word $3000
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</PRE>
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</CODE></BLOCKQUOTE>
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Since the variable is of type <CODE>void</CODE> you may not use it as is.
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However, taking the address of the variable results in a <CODE>void*</CODE>
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which may be passed to any function expecting a pointer.
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See the
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<A HREF="geos.html">GEOS library document</A> for examples
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on how to use this feature.
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</LI>
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<LI> cc65 implements flexible array struct members as defined in the C99 ISO
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standard. As an extension, these fields may be initialized. There are
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several exceptions, however (which is probably the reason why the
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standard does not define this feature, because it is highly
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unorthogonal). Flexible array members cannot be initialized ...
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<UL>
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<LI>... when defining an array of structs with flexible
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members.</LI>
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<LI>... if such a struct is a member field of another struct
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which is not the last field.</LI>
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<LI>... if the struct which contains a flexible array member is
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declared as <CODE>register</CODE>, and the size and compiler settings
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do allow the compiler actually to place the struct into the
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register bank in the zero page.</LI>
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</UL>
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Please note that -- as defined in the ISO C standard -- the <CODE>sizeof</CODE>
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operator returns the struct size with the flexible array member having
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size zero, even if it is initialized.
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</LI>
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</UL>
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</P>
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<HR>
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<A HREF="cc65-6.html">Next</A>
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<A HREF="cc65-4.html">Previous</A>
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<A HREF="cc65.html#toc5">Contents</A>
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