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Forums > C64 Coding > Fast way to rotate a char?
2017-01-04 09:32
Rudi

Registered: May 2010
Posts: 82
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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2017-01-13 21:41
Rudi

Registered: May 2010
Posts: 82
No, I dont think thats a good idea. But feel free to restrict yourselves to your own rules. I totally dont know what you are talking about anyway...
2017-01-13 22:31
Color Bar

Registered: Oct 2012
Posts: 98
Quote: No, I dont think thats a good idea. But feel free to restrict yourselves to your own rules. I totally dont know what you are talking about anyway...

OK, I will keep mentioning both cases (all input and output bytes either in ZP or in Mem).

One version uses 301 cycles if all are in ZP, another version takes 327 cycles when all are in Mem.
2017-01-14 04:56
ChristopherJam

Registered: Aug 2004
Posts: 503
OK, in that case mine is 292 cycles if source and dest are in ZP, 308 cycles when all in mem.

Here's a diagram of the how the bits are shuffled at each stage:
Each block shows two input bytes for a swap macro in the top half, two outputs in the lower half. Digits in left border of each box are indexes into the input/output arrays for that stage.
Note that each input pair for the last four blocks contain one byte that's a shuffled version of an output byte from the previous stage, marked with a *
Shuffle's so I can then do an Axis style swap (which needs half the bits to be correctly located within the byte), and it's performed by storing the result of the previous stage into the low byte of an LDY absolute that references the shuffle table.

 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+
 0 a0 b0 c0 d0 e0 f0 g0 h0 |  1 a1 b1 c1 d1 e1 f1 g1 h1 |  2 a2 b2 c2 d2 e2 f2 g2 h2 |  3 a3 b3 c3 d3 e3 f3 g3 h3 |
 4 a4 b4 c4 d4 e4 f4 g4 h4 |  5 a5 b5 c5 d5 e5 f5 g5 h5 |  6 a6 b6 c6 d6 e6 f6 g6 h6 |  7 a7 b7 c7 d7 e7 f7 g7 h7 |
 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+
 0 a0 b0 c0 d0 a4 b4 c4 d4 |  1 c1 d1 a1 b1 c5 d5 a5 b5 |  2 c2 d2 a2 b2 c6 d6 a6 b6 |  3 a3 b3 c3 d3 a7 b7 c7 d7 |
 4 e0 f0 g0 h0 e4 f4 g4 h4 |  5 g1 h1 e1 f1 g5 h5 e5 f5 |  6 g2 h2 e2 f2 g6 h6 e6 f6 |  7 e3 f3 g3 h3 e7 f7 g7 h7 |
 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+
                                                             
                                                             
 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+
 0 a0 b0 c0 d0 a4 b4 c4 d4 |  1 c1 d1 a1 b1 c5 d5 a5 b5 |  4 e0 f0 g0 h0 e4 f4 g4 h4 |  5 g1 h1 e1 f1 g5 h5 e5 f5 |
 2 c2 d2 a2 b2 c6 d6 a6 b6 |  3 a3 b3 c3 d3 a7 b7 c7 d7 |  6 g2 h2 e2 f2 g6 h6 e6 f6 |  7 e3 f3 g3 h3 e7 f7 g7 h7 |
 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+
 0 a0 b0 a2 b2 a4 b4 a6 b6 |  1 c1 d1 c3 d3 c5 d5 c7 d7 |  4 e0 f0 e2 f2 e4 f4 e6 f6 |  5 g1 h1 g3 h3 g5 h5 g7 h7 |
 2 c2 d2 c0 d0 c6 d6 c4 d4 |  3 a3 b3 a1 b1 a7 b7 a5 b5 |  6 g2 h2 g0 h0 g6 h6 g4 h4 |  7 e3 f3 e1 f1 e7 f7 e5 f5 |
 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+
                                                             
                                                             
 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+
 0 a0 b0 a2 b2 a4 b4 a6 b6 |  1 c1 d1 c3 d3 c5 d5 c7 d7 |  4 e0 f0 e2 f2 e4 f4 e6 f6 |  6*g0 h0 g2 h2 g4 h4 g6 h6 |
 3*a1 b1 a3 b3 a5 b5 a7 b7 |  2*c0 d0 c2 d2 c4 d4 c6 d6 |  7*e1 f1 e3 f3 e5 f5 e7 f7 |  5 g1 h1 g3 h3 g5 h5 g7 h7 |
 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+
 0 a0 a1 a2 a3 a4 a5 a6 a7 |  3 d0 d1 d2 d3 d4 d5 d6 d7 |  4 e0 e1 e2 e3 e4 e5 e6 e7 |  6 g0 g1 g2 g3 g4 g5 g6 g7 |
 1 b0 b1 b2 b3 b4 b5 b6 b7 |  2 c0 c1 c2 c3 c4 c5 c6 c7 |  5 f0 f1 f2 f3 f4 f5 f6 f7 |  7 h0 h1 h2 h3 h4 h5 h6 h7 |
 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+


2017-01-15 11:29
Color Bar

Registered: Oct 2012
Posts: 98
Quoting ChristopherJam
OK, in that case mine is 292 cycles if source and dest are in ZP, 308 cycles when all in mem.
Quote:

Ver neat!
Quote:

 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+
 0 a0 b0 c0 d0 e0 f0 g0 h0 |  1 a1 b1 c1 d1 e1 f1 g1 h1 |  2 a2 b2 c2 d2 e2 f2 g2 h2 |  3 a3 b3 c3 d3 e3 f3 g3 h3 |
 4 a4 b4 c4 d4 e4 f4 g4 h4 |  5 a5 b5 c5 d5 e5 f5 g5 h5 |  6 a6 b6 c6 d6 e6 f6 g6 h6 |  7 a7 b7 c7 d7 e7 f7 g7 h7 |
 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+
 0 a0 b0 c0 d0 a4 b4 c4 d4 |  1 c1 d1 a1 b1 c5 d5 a5 b5 |  2 c2 d2 a2 b2 c6 d6 a6 b6 |  3 a3 b3 c3 d3 a7 b7 c7 d7 |
 4 e0 f0 g0 h0 e4 f4 g4 h4 |  5 g1 h1 e1 f1 g5 h5 e5 f5 |  6 g2 h2 e2 f2 g6 h6 e6 f6 |  7 e3 f3 g3 h3 e7 f7 g7 h7 |
 +-------------------------+  +-------------------------+  +-------------------------+  +-------------------------+

I would implement the code for the second and third byte pairs like this
lax s1
lda shuffle1,x
and #$f0
ldy s2
ora merge1,y
sta tmp1
tya
lda shuffle2,y
and #$0f
ora merge2,x
sta tmp2
------------------+
36 cycles (s1 and s2 in mem, tmp1 and tmp2 in zp)

For the first and 4th byte pairs the "LDA shuffle"s can be omitted (28 cycles).
Is there a more efficient way to do it?
2017-01-15 14:37
Oswald

Registered: Apr 2002
Posts: 3990
why shuffle tabs dont include the ANDs?
2017-01-15 18:29
Color Bar

Registered: Oct 2012
Posts: 98
Yes, you are right, the tables should include the ANDs. So that makes it 32 cycles for the 2nd and 3rd byte pairs.
2017-01-16 09:04
Axis/Oxyron

Registered: Apr 2007
Posts: 79
Quoting Color Bar

tya
lda shuffle2,y


WOOT? ;o)
2017-01-16 09:16
Pex Mahoney Tufvesson

Registered: Sep 2003
Posts: 32
> WOOT? ;o)

It's a new way of doing nothing; it's just a little too complicated for you Axis, so go back and play with your 300fps million-dots 6510 dot spheres. :P

---
Have a noise night!
http://mahoney.c64.org
2017-01-16 10:03
Color Bar

Registered: Oct 2012
Posts: 98
Quote: Quoting Color Bar

tya
lda shuffle2,y


WOOT? ;o)


Lol. I needed some sleep. Honestly, this stuff is keeping me awake at night.

Pex: Good that you contribute something to this thread too.
2017-01-16 12:30
ChristopherJam

Registered: Aug 2004
Posts: 503
Haha, you guys.

Um, my second and third shuffles from the first phase is pretty brute force on the tables front:

    ldx s1
    ldy s2
    lda sb_t2,x
    ora sb_t3,y
    sta d1
    lda sb_t0,x
    ora sb_t1,y
    sta d2


30 cycles with mem source, zp destination..
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