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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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chatGPZ
Registered: Dec 2001
Posts: 11386 |
tlr: wasnt there some VIC that only clears (or retriggers?) the collisions once? |
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tlr
Registered: Sep 2003
Posts: 1790 |
Quote: tlr: wasnt there some VIC that only clears (or retriggers?) the collisions once?
That was lightpen triggering. It's working very differently on 6569R1. |
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Skate
Registered: Jul 2003
Posts: 494 |
I just made a rough calculation. Using 16k of precalc data (which is already terrible), each char takes 500-600 cycles to rotate. So, c2p routine looks like the best solution in every aspect. I'm still thinking an alternative approach though. |
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Flavioweb
Registered: Nov 2011
Posts: 463 |
Quoting SkateI just made a rough calculation. Using 16k of precalc data (which is already terrible), each char takes 500-600 cycles to rotate.
Just to say (...maybe i'm off-topic...) this code took 544 cicles rotate a char counterclockwise.
*=$C000
.FOR S=0, S<8, S=S+1
LDA SOURCE+S
.FOR D=0, D<8, D=D+1
ASL
ROL DEST+D
.NEXT
.NEXT
RTS
;-------------------
SOURCE
.BYTE %11111111
.BYTE %10000000
.BYTE %01000000
.BYTE %00100000
.BYTE %00010000
.BYTE %00001000
.BYTE %00000100
.BYTE %11111111
DEST
.BYTE %00000000
.BYTE %00000000
.BYTE %00000000
.BYTE %00000000
.BYTE %00000000
.BYTE %00000000
.BYTE %00000000
.BYTE %00000000
;--------------------------------------- |
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Rudi
Account closed
Registered: May 2010
Posts: 125 |
This takes ~472 cycles, and is basically similar to Oswalds approach: ;counter-clockwise rotation by 90 degrees.
;column 1
ror $74
rol
ror $75
rol
ror $76
rol
ror $77
rol
ror $78
rol
ror $79
rol
ror $7a
rol
ror $7b
rol
sta $7c
;tot = 59 cycles
;column 2
ror $74
rol
ror $75
etc..
ror $7b
rol
sta $83
;tot = 59*8 = 472 cycles did a test in zp. so rotated (destination) bytes are in $7c to $83. this req eight bytes to be copied to zeropage ($74 to $7b) (as an example). |
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Oswald
Registered: Apr 2002
Posts: 5094 |
axis' one is close to max possible I guess, go for it if understandable version is not enough :) |
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Skate
Registered: Jul 2003
Posts: 494 |
Table lookup doesn't necessarily be faster than bit shifting. What i was saying is even using large tables to get rid of bit shifting doesn't save cycles unless you start thinking out of the box. |
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Skate
Registered: Jul 2003
Posts: 494 |
here is an algo which looks similar to c2p method without 8 bit restrictions.
void transpose8(unsigned char A[8], int m, int n,
unsigned char B[8]) {
unsigned x, y, t;
// Load the array and pack it into x and y.
x = (A[0]<<24) | (A[m]<<16) | (A[2*m]<<8) | A[3*m];
y = (A[4*m]<<24) | (A[5*m]<<16) | (A[6*m]<<8) | A[7*m];
t = (x ^ (x >> 7)) & 0x00AA00AA; x = x ^ t ^ (t << 7);
t = (y ^ (y >> 7)) & 0x00AA00AA; y = y ^ t ^ (t << 7);
t = (x ^ (x >>14)) & 0x0000CCCC; x = x ^ t ^ (t <<14);
t = (y ^ (y >>14)) & 0x0000CCCC; y = y ^ t ^ (t <<14);
t = (x & 0xF0F0F0F0) | ((y >> 4) & 0x0F0F0F0F);
y = ((x << 4) & 0xF0F0F0F0) | (y & 0x0F0F0F0F);
x = t;
B[0]=x>>24; B[n]=x>>16; B[2*n]=x>>8; B[3*n]=x;
B[4*n]=y>>24; B[5*n]=y>>16; B[6*n]=y>>8; B[7*n]=y;
}
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HCL
Registered: Feb 2003
Posts: 728 |
Ah, that's just beautiful Axis!!
..as usual, i'm the last one to read the thread.. but if anyone still wonders what that code does, it is mirroring the 8x8-matrix by starting with 2x2-bit-blocks, then 4x4-blocks, then finally the whole 8x8-block. Mirroring and rotation is of course just a matter of configuring the macros :).
..and of course Graham did this 15+ years ago, hope that makes you all feel as retard as i do ;). |
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Pex Mahoney Tufvesson
Registered: Sep 2003
Posts: 52 |
I used Rudi's 472-cycle approach "This takes ~472 cycles, and is basically similar to Oswalds approach" in Storebror
There was no need to make it any faster, since it was a one-time calculation just before the android starts rotating. My routine included not only rotation, but mirroring across horizontal, vertical and diagonals as well.
And HCL... I'm even later than you are. So don't worry, you're ok! ;)
---
Have a noise night!
http://mahoney.c64.org |
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