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Portable Network Graphic  |  1997-07-26  |  132KB  |  816x1056  |  8-bit (256 colors)
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OCR: Sat, Feb 17 1996 Beginners Guide Macintosh Assembly Language Programming Bage Next we get the physical number of bytes on each line with the move.w screenrow Ip' instruction. This moves the number of bytes in each screen line into d DI used as a counter to count the bytes on each line as they are cleared, however... Clearing the screen byte by byte quite a slow to op in 256 colour mode on a14 inch screen there are over 490,000 bytes to be cleared. Instead we clear longs, which reduces the number of clears by factor of 4 as a long IS 4 bytes. If we are clearing bytes in one go. then the number of time we have to clear 4 bytes IS reduced by factor Hence theLSR W instruction. Shifting number right by is the same as dividing by so we shift it right twice. we divide it by this far quicker than ...