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Rudi
Account closed
Registered: May 2010
Posts: 125 |
Fast way to rotate a char?
Im not talking about rol or ror, but swap bits so that they are rotated 90 degrees:
Example:
a char (and the bits can be random):
10110010 byte 1..
11010110 byte 2.. etc..
00111001
01010110
11011010
10110101
00110011
10110100 after "rotation" (rows and columns are swapped):
11001101
01011000
10100111
11111111
00101000
01010101
11011010
00100110 is it possible to use lookup tables for this or would that lookup table be too big?
or other lookuptable for getting and setting bits?
-Rudi |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
@Krill: Nice!!!
So, now what about the shortest code to rotate a char? (or a reference to the message number if it's already stated here) |
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Krill
Registered: Apr 2002
Posts: 2980 |
Jackasser: Shortest? Going fully academic, eh? =D
I guess it would be the naïve approach, in a nested loop (untested):SOURCE = $02
DEST = $0a
ldy #7 ; 2
- ldx #7 ; 2
- lsr SOURCE,x; 2
ror ; 1
dex ; 1
bpl - ; 2
sax DEST,y ; 2
dey ; 1
bpl -- ; 215 bytes.
But i'd rather have a faster than 280-ish cycles approach. =) |
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Oswald
Registered: Apr 2002
Posts: 5094 |
sax for giggles ? |
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Krill
Registered: Apr 2002
Posts: 2980 |
SAX because STA zp,Y does not exist. |
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Oswald
Registered: Apr 2002
Posts: 5094 |
*clapping* |
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