> Is there a faster way than this to get the absolute value of
the accumulator?
>
> (...)
>
> BPL plus
> EOR #$FF
> CLC
> ADC #1
> plus:
>Assuming that you mean A is an 8 bit signed number (-128 to
+127), and that
>you just want to get rid of the sign, try this:
>AND #%01111111 ; this should mask off the sign bit
> ; note that abs(-128) would be 0 using
this method
Uhhhmmm! I don't think this will work. For signed 8-bit
numbers:
-1 = %11111111
-2 = %11111110
-3 = %11111101
etc...
so -1 AND %0111111 = 127 (incorrect!)
i.e. %11111111 AND %01111111 = %01111111
The reason for two's complement notation is that you can do 36
+ -2 = 34 (%00100100 + %11111110) and it works...
Matt Pritchard
graphics_grunt@ensemble_studios
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