Log inRegister an accountBrowse CSDbHelp & documentationFacts & StatisticsThe forumsAvailable RSS-feeds on CSDbSupport CSDb Commodore 64 Scene Database
You are not logged in 
CSDb User Forums


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
 
... 98 posts hidden. Click here to view all posts....
 
2017-01-08 15:54
Bitbreaker

Registered: Oct 2002
Posts: 418
Quoting Axis/Oxyron
But 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 :-)
2017-01-08 16:22
Rudi

Registered: May 2010
Posts: 82
XAA might be something too.
2017-01-08 19:29
Rudi

Registered: May 2010
Posts: 82
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.
2017-01-09 08:35
Bitbreaker

Registered: Oct 2002
Posts: 418
Besides that it will produce rubbish as xaa can add some unpredictable value to A before doing the txa and and part :-)
2017-01-09 11:10
Color Bar

Registered: Oct 2012
Posts: 98
Quoting Color Bar
I 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.
2017-01-09 12:52
Rudi

Registered: May 2010
Posts: 82
Quote: Quoting Color Bar
I 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?
2017-01-09 13:25
Axis/Oxyron

Registered: Apr 2007
Posts: 79
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.
2017-01-09 15:27
Rudi

Registered: May 2010
Posts: 82
Interesting ideas. Reordering merges was something I tried out but failed. Maybe I should look at it again.
2017-01-09 16:00
Rudi

Registered: May 2010
Posts: 82
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.
2017-01-09 16:11
Color Bar

Registered: Oct 2012
Posts: 98
Quote: Are you using the masking method?

These diagrams illustrate what I am thinking of

xxxxxxxx source0
xxxxxxxx source1
xxxxxxxx
xxxxxxxx
aabbccdd
aabbccdd
aabbccdd
aabbccdd source7

xxxxaaaa destination0
xxxxaaaa destination1
xxxxbbbb
xxxxbbbb
xxxxcccc
xxxxcccc
xxxxdddd
xxxxdddd destination7

The source bits in the block indicated by the a's should end up in the proper locations in destination bytes. Using look up tables the 8 a's are put into one byte such that the high nybble is the desired nybble of destination0 and then the low nybble that of destination1. The same procedure can be followed for all 4x2 source blocks 'b','c','d', etcetera.

Code for doing that can look like
ldy source4
lda mergingTable1,y  ;This table takes two bits and puts them in a byte, such that they are in the right positions to use as nybble for the destination.
ldx source5
ora mergingTable2,x
ldx source6
ora mergingTable3,x
ldx source7
ora mergingTable4,x  ;Now the byte is filled with all bits from block 'a'.

tax
and #$0f
sta destination0
lda moveHighNybbleToLowNybble,x
sta destination1
-------------------+
42 cycles.

This has to be repeated for blocks 'b', 'c', 'd' (using the right lookup tables), but since source4 was saved in Y, that code can start with TAY instead of 'LDY source4' to save 1 cycle.

The lower half of the source matrix is therefore moved in 42+3*41 = 165 cycles.

The other half of the matrix goes very similar, but since the destination bytes are no longer empty, we have to add 'ORA destination0' and 'ORA destination1' before the 'STA destination0' and 'STA destination1', respectively. So that will take 4*6 cycles extra, totalling 2*165+24=354 cycles. But the method is very memory inefficient.
Previous - 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 - Next
RefreshSubscribe to this thread:

You need to be logged in to post in the forum.

Search the forum:
Search   for   in  
All times are CET.
Search CSDb
Advanced
Users Online
Dymo
grennouille
E$G/I-IokutO ForcE
Pantaloon/Fairlight
Yogibear/Protovision
Guests online: 51
Top Demos
1 Uncensored  (9.7)
2 Edge of Disgrace  (9.7)
3 Coma Light 13  (9.6)
4 Lunatico  (9.6)
5 Comaland 100%  (9.5)
6 Wonderland XII  (9.5)
7 Incoherent Nightmare  (9.5)
8 Comaland  (9.5)
9 Fantasmolytic  (9.5)
10 Wonderland XIII  (9.5)
Top onefile Demos
1 Globe 2016 [reu]  (9.6)
2 Dawnfall V1.1  (9.5)
3 SpongeBog Demo  (9.5)
4 Daah, Those Acid Pil..  (9.4)
5 Treu Love [reu]  (9.4)
6 Dawnfall  (9.3)
7 One-Der  (9.2)
8 Hardware Accelerated..  (9.2)
9 Goatbeard  (9.1)
10 Safe VSP  (9.1)
Top Groups
1 Censor Design  (9.4)
2 Booze Design  (9.4)
3 Oxyron  (9.4)
4 Crest  (9.3)
5 Arsenic  (9.3)
Top Mega Swappers
1 Nightshade  (9.4)
2 Aslive  (9.3)
3 Calypso  (9.2)
4 Dishy  (9.0)
5 R.C.S.  (8.8)

Home - Disclaimer
Copyright © No Name 2001-2017
Page generated in: 0.141 sec.