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93 lines
2.9 KiB
HTML
93 lines
2.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
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<title>xAsm Integer/Boolean expressions</title>
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<link rel="stylesheet" type="text/css" href="../style.css">
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</head>
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<body>
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<h1>Integer and Boolean expressions</h1>
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<p>An expression can be composed of many things. Expressions are always evaluated using signed 32-bit math.</p>
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<p>The most basic expression is just a single number.</p>
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<h2>Numeric Formats</h2>
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<p>xAsm has a number of numeric formats.</p>
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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 the “chunky” data to “planar” data as used in the Gameboy.</p>
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<pre>DW `01012323</pre>
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<p>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.</p>
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<h2>Operators</h2>
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<p>A great number of operators you can use in expressions are available (listed in order of precedence):</p>
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<table>
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<caption>Operators</caption>
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<thead>
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<tr>
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<th scope="col">Operator</th>
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<th scope="col">Meaning</th>
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</tr>
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</thead>
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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.</p>
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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.</p>
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<h1>See also:</h1>
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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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<hr>
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<p>Last updated 21 June 1997 by <a href="mailto:surfsmurf@matilde.demon.co.uk">Carsten Sorensen</a></p>
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</body>
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</html>
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