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The code comes from the RGBDS source and documentation zip files found on this website: http://www.otakunozoku.com/1999/08/01/rednex-gameboy-development-system/ The same website reports: "Best of all, it’s free! That’s right! Free! The executables are free to use, either for personal hobby use, or full blown commercial productions — I know of at least a dozen commercial games you can purchase that are written with RGBDS — and the source code is free to modify. "The only thing I ask is that you do not charge for either distributing the executables or source code, and any derivative works you give credit to the original authors of the tools. That means you have to say “Thanks” to the original authors SurfSmurf and Otaku." Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
103 lines
3.0 KiB
HTML
103 lines
3.0 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<HTML>
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<HEAD>
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<TITLE>xAsm Integer/Boolean expressions</TITLE>
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</HEAD>
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<BODY BGCOLOR="#692764" TEXT="#F5A0D8" LINK="#8AAEE6" VLINK="#2B9DA4" ALINK="#95F0DA">
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<I><H2>Integer and Boolean expressions
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</H2></I>
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<HR>
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<P>An expression can be composed of many things. Expressions are always evaluated using signed 32-bit math.
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<P>The most basic expression is just a single number.
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<H4><BR>Numeric Formats</H4>
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<P>xAsm has a number of numeric formats.
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<UL>
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<LI>Hexadecimal: $0123456789ABCDEF. Case-insensitive
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<LI>Decimal: 0123456789
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<LI>Octal: &01234567
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<LI>Binary: %01
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<LI>Fixedpoint (16.16): 01234.56789
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<LI>Character constant: "ABYZ"
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<LI>Gameboy graphics: `0123
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</UL>
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<P>The last one, Gameboy graphics, is quite interesting and useful. The values are actually pixel values and it converts
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the "chunky" data to "planar" data as used in the Gameboy.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE>DW `01012323</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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Admittedly an expression with just a single number is quite boring. To spice things up a bit there's a few operators you can use to perform calculations between numbers.
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<H4><BR>
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Operators</H4>
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<P>A great number of operators you can use in expressions are available (listed in order of precedence):
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<TABLE BORDER=1>
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<CAPTION><I>Operators</I></CAPTION>
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<TR>
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<TD><B><I>Operator</I></B></TD>
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<TD><B><I>Meaning</I></B></TD>
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</TR>
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<TR>
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<TD>( )</TD>
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<TD>Precedence override</TD>
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</TR>
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<TR>
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<TD>FUNC()</TD>
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<TD>Functioncall</TD>
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</TR>
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<TR>
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<TD>~ + -</TD>
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<TD>Unary not/plus/minus</TD>
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</TR>
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<TR>
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<TD>* / %</TD>
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<TD>Multiply/divide/modulo</TD>
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</TR>
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<TR>
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<TD><< >></TD>
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<TD>Shift left/right</TD>
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</TR>
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<TR>
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<TD>& | ^</TD>
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<TD>Binary and/or/xor</TD>
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</TR>
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<TR>
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<TD>+ -</TD>
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<TD>Add/subtract</TD>
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</TR>
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<TR>
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<TD>!= == <= >= < ></TD>
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<TD>Boolean comparison</TD>
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</TR>
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<TR>
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<TD>&& ||</TD>
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<TD>Boolean and/or</TD>
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</TR>
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<TR>
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<TD>!</TD>
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<TD>Unary Boolean not</TD>
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</TR>
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</TABLE>
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<P>The result of the boolean operators is zero if when FALSE and non-zero when TRUE. Thus it is legal to use an integer as the condition for <A HREF="if.htm">IF</A> blocks. You can use symbols instead of numbers in your expression if you wish.
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<P>An expression is said to be constant when it doesn't change its value during linking. This basically means that you can't use labels in those expressions. The instructions in the macro-language all require expressions that are constant<BR>
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<H3>See also:</H3>
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<UL>
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<LI><A HREF="symbols.htm">Symbols</A>
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<LI><A HREF="expr_fix.htm">Fixed-point expressions and functions</A>
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<LI><A HREF="expr_str.htm">String expressions, functions and formatting</A>
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<LI><A HREF="miscfunc.htm">Other functions</A>
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</UL>
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<BR><HR>
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<FONT SIZE="-1"><I><P ALIGN=RIGHT>Last updated 21 June 1997 by <A HREF="mailto:surfsmurf@matilde.demon.co.uk">Carsten Sorensen</A></P></I></FONT>
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