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Shifting consecutive LONGs
I have n consecutive LONGs in Cog RAM, representing a bitmap scan line, which I want to shift en masse left by some amount in order to implement pixel-fine scrolling.
Each pixel is represented by 8 bits, and there are 320 pixels visible per scan line, so at 4 pixels per LONG (32/8=4) I have a buffer of 80 pixels.
The issue is that due to the long-aligned memory model, I can only "scroll" (i.e. shift left or right) 1 LONG or 4 pixels at a time trivially.
To scroll 8 bits at a time, as far as I can tell, would require instruction-intensive offset calculating and shifting and masking and etc etc etc in order to move all pixels left or right arbitrarily (aka not multiples of 4 pixels).
Is there any efficient way via PASM or otherwise to shift all longs from 0 to n by 3, 2, or 1 pixels (i.e. 24, 16, or 8 bits)?