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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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Rudi
Account closed
Registered: May 2010
Posts: 125 |
Quote: But you know that:
(i ^ (i & 0xcc))
is the same as:
i & 0x33
;o)
No, didnt think about that hehe.
Btw, 312 cycles now (with LAX). |
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Bitbreaker
Registered: Oct 2002
Posts: 504 |
Quoting Axis/OxyronBut you know that:
(i ^ (i & 0xcc))
is the same as:
i & 0x33
;o)
smells like the version of the tab that shifts only 1 bit to the right could be substituted by some asr magic?
Also the and maskX looks like it could be included into something, too static to be done that often :-) |
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Rudi
Account closed
Registered: May 2010
Posts: 125 |
XAA might be something too. |
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Rudi
Account closed
Registered: May 2010
Posts: 125 |
Here's a different approach to it:ldx $82 ;3
xaa #$33 ;2 a=(x & 0x33)
ldy $80 ;3
eor shl2_eor_cc, y ;4*
sta $90 ;3
lda shr2_eor_33, x ;4*
eor tab_cc, y ;4*
sta $92 ;3 uses the same amount of cycles though.
Bitbreaker: yes, one could probably optimize the 1x1 rotator with other illegal-opcodes. sine some of them do one shift. |
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Bitbreaker
Registered: Oct 2002
Posts: 504 |
Besides that it will produce rubbish as xaa can add some unpredictable value to A before doing the txa and and part :-) |
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Rastah Bar
Account closed
Registered: Oct 2012
Posts: 336 |
Quoting Color BarI may have found a method that takes 432 cycles....
If I merge columns of 2 bits wide and 4 bits high into one byte and then extract the destination nybbles I can reduce that to 354 cycles. |
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Rudi
Account closed
Registered: May 2010
Posts: 125 |
Quote: Quoting Color BarI may have found a method that takes 432 cycles....
If I merge columns of 2 bits wide and 4 bits high into one byte and then extract the destination nybbles I can reduce that to 354 cycles.
Are you using the masking method? |
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Axis/Oxyron
Account closed
Registered: Apr 2007
Posts: 91 |
I just want to share some thoughts on my merges that didnt work out. Perhaps I´m just missing the last twist.
First idea was to make relative merges. I discussed that back in the 90´s with some Amiga coders and on 68030-68060 it saves some cycles.
Idea is, that shifting of the input must not always have the exact values, as long as the delta of the shift of the 2 inputs stays correct. Disadvantage of that is, that the last merge needs to make some rol/ror to compensate.
This resulted in something like this:
lda {src1}
ldy {src2}
and #$aa
ldx {bittab1},y
sax {dst1}
eor {src1} ;invert and #$aa to and #$55
ldx {bittab2},y
sax {dst2}
Unluckily it only saves 1 cycle per merge which is completely eaten up by the last merge that looses 2 cycles for the correction.
Another idea was to interleave the temp-arrays with hi-byte pointers so that they can be used both as pointers for indirect y-indexing and as direct values. Code would look like this:
lax {src1}
and #{mask1}
ora ({src2}),y
sta {dst1}
lda ({src2}),y
ora {bittab2},x
sta {dst2}
Would also save 1 cycle per merge. But the unsolved problem is, that the 2 usages of {src2} should be pointing to 2 different tables. *grrr*
What definitely works is reordering the merges, so that the last 2 merges of a resolution dont need to store the tmp-values into the zp and the first two of the next resolution doesnt need to read the tmp-values.
so the last
sta {dst2}
and the first
lax {src1}
would merge into
tax.
Saves 4 times 3=12 cycles. |
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Rudi
Account closed
Registered: May 2010
Posts: 125 |
Interesting ideas. Reordering merges was something I tried out but failed. Maybe I should look at it again. |
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Rudi
Account closed
Registered: May 2010
Posts: 125 |
Ok, so I did merge 4x4 and 2x2, and it worked. Am now at 299 cycles. There is probably more that can be optimized, because now the code looks like a mess. |
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