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53 lines
1.4 KiB
C
53 lines
1.4 KiB
C
/* ------------------------------------------------------------------------
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System : Manx Aztec C65 Version 3.2b
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MS-DOS cross-development environment
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Platform : Apple IIe 128K PRODOS 8
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Program : hibase2.c
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Description : G2 Library Routine
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Written by : Bill Buckels
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Revision Date: March 3, 1991
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Licence : You may use this code for whatever you wish as long
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as you agree that Bill Buckels has no warranty or
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liability obligations whatsoever from said use.
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------------------------------------------------------------------------ */
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/* use hibase2.c instead... this routine was modified from
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the original aztec C library but it is too processor intensive
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for real purposes... a table works best despite the larger
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data segment... see hibase2.c */
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/* provides base address for page2 hires scanlines */
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/* does not bother to check whether we are in range */
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/* gets the address as quickly as possible */
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/* stays away from processor intensive mul and div */
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gethibase(currentline,currentbase)
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int currentline;
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int *currentbase;
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{
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int ybase=0x4000,z,a;
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if(currentline >63)
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{
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if (currentline < 128)
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{
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ybase+=0x28;
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currentline-=64;
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}
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else
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{
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ybase+=0x50;
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currentline-=128;
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}
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}
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z=(currentline>>3);
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a = (z<<7)|ybase;
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*currentbase = (currentline - (z<<3))<<10 | a;
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}
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