39 lines
928 B
Plaintext
39 lines
928 B
Plaintext
<!doctype linuxdoc system>
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<article>
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<title>Special math functions
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<author>Christian Krüger
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<abstract>
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This library provides functions for speed optimized math operations.
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</abstract>
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<!-- Table of contents -->
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<toc>
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<!-- Begin the document -->
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<sect>Multiplication<p>
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When accessing screen memory often a multiplication of the vertical position is needed to calculate
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the target address. A quite common horizontal span for 8-bit systems is 20 or 40 bytes (beside e.g. 32 bytes, where the multiplication can be accomplished by shifting 5 times).
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<p>
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<tscreen><verb>
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unsigned int __fastcall__ _mul20(unsigned char value);
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</verb></tscreen>
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The 8 bit <tt>value</tt> is multiplied by 20 and returned as 16 bit value.
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</p>
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<p>
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<tscreen><verb>
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unsigned int __fastcall__ _mul40(unsigned char value);
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</verb></tscreen>
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The 8 bit <tt>value</tt> is multiplied by 40 and returned as 16 bit value.
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</p>
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</article>
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