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104 lines
3.1 KiB
HTML
104 lines
3.1 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
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"http://www.w3.org/TR/html4/loose.dtd">
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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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