How can I flip bits in SX/B?

T&E Engineer · 2009-05-21 00:24

If I have a variable tmpB3 which·let's say looks·something like this: %11001010 and I want the bits to be fliped so it now is: %01010011

How can this be done?

More specifically·I have a data statement with a character (or really lots of characters in DATA statements):

UC_Letter_A:
DATA· %01111100 'A
DATA· %00010010
DATA· %00010001
DATA· %00010010
DATA· %01111100

and I don't want to have to retype every character in flipped again but I need this:

UC_Letter_A:
DATA· %00111110·'A (flipped bits)
DATA· %01001000
DATA· %10001000
DATA· %01001000
DATA· %00111110

There should be a way to read it in and flip the bits. How can this be done in SX/B 2.0?

Thanks for your help!
·

Zoot · 2009-05-21 01:37

You mean "reverse" the bit order? There is no command for it. Unrolling a loop is probably the most compact way to do it...


READ someAddr, tmpB99

tmpB3.0 = tmpB99.7
tmpB3.1 = tmpB99.6
tmpB3.2 = tmpB99.5
tmpB3.3 = tmpB99.4
tmpB3.4 = tmpB99.3
tmpB3.5 = tmpB99.2
tmpB3.6 = tmpB99.1
tmpB3.7 = tmpB99.0

Of course, you can write a function with two bit masks if you need to operate on a wide swatch of variables with variable reverse counts and lengths (a la the Stamp REV operator), or you can use two other temps or a local stack and load 'em up as parameters...


FUNC revBits
__PARAM2.0 = __PARAM1.7
__PARAM2.1 = __PARAM1.6
__PARAM2.2 = __PARAM1.5
__PARAM2.3 = __PARAM1.4
__PARAM2.4 = __PARAM1.3
__PARAM2.5 = __PARAM1.2
__PARAM2.6 = __PARAM1.1
__PARAM2.7 = __PARAM1.0
   RETURN __PARAM2

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Bean · 2009-05-21 02:34

DEVICE SX28, OSC4MHZ 
FREQ 4_000_000 

 
origData VAR BYTE 
flipData VAR BYTE 

 
PROGRAM Start NOSTARTUP 

 
Start: 
  origData = %11001010 
  ASM 'flipData = OrigData with bits flipped; NOTE: Destoys value in origData 
    RR origData 
    RL flipData 
    RR origData 
    RL flipData 
    RR origData 
    RL flipData 
    RR origData 
    RL flipData 
    RR origData 
    RL flipData 
    RR origData 
    RL flipData 
    RR origData 
    RL flipData 
    RR origData 
    RL flipData 
  ENDASM 
END

Bean

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·

Zoot · 2009-05-21 03:25

Nice. "C"lever use of C flag.

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When the going gets weird, the weird turn pro. -- HST

1uffakind.com/robots/povBitMapBuilder.php
1uffakind.com/robots/resistorLadder.php

T&E Engineer · 2009-05-21 14:51

Thank you guys very much!

I thought about Zoot's first approach but was locked into thinking I could use a FOR NEXT loop which failed as seen in another post from PJ Allen.

e.g.

j = 7

FOR i = 0 TO 7

tmp4.j = tmp3.i

j=j-1

NEXT

However, sometimes you need to break it down to the simplest form like Zoot did. This is working but I have other minor issues to deal with (which I will try to work out before I ask for help).

I am writing code for the new 0832 Display boards and have it almost working but these boards use nibbles not bytes so it's a bit awkward: http://www.sureelectronics.net/goods.php?id=903

PS: Is there any advantage (e.g. significant speed difference or saving ram space, etc.) using Bean's assembly language routine as I am not familiar with this as much as SX/B?

Thanks again guys!

Peter Verkaik · 2009-05-21 15:23

More on reversing bits:
http://www.sxlist.com/techref/ubicom/lib/math/bit/revbits_sx.htm

regards peter
·

Zoot · 2009-05-21 17:11

Bean's code is way more compact... var.0 = var.7 compiles to a MOVB which is 4 instructions per bit or 32 instructions to re-map a byte. Bean's code is half that.

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When the going gets weird, the weird turn pro. -- HST

1uffakind.com/robots/povBitMapBuilder.php
1uffakind.com/robots/resistorLadder.php

JonnyMac · 2009-05-22 00:49

I wrote a library of bit-oriented routines for the SX -- in it you'll find functions that will reverse the bits in a byte and in a word.

' Use: result = FLIP_BYTE aByte
' -- flips bits in byte end-to-end

FUNC FLIP_BYTE
  '{$IFUSED FLIP_BYTE}
  ASM
    MOV   __PARAM2, __PARAM1                    ' make copy to __PARAM2
    CLR   __PARAM3                              ' clear count

FB_Loop:
    RR    __PARAM2                              ' get bit from __PARAM2
    RL    __PARAM1                              ' move into __PARAM1
    INC   __PARAM3                              ' update count
    JNB   __PARAM3.3, @FB_Loop                  ' abort at 8
  ENDASM
  '{$ENDIF}
  ENDFUNC

' Use: result = FLIP_WORD aWord
' -- flips bits in word end-to-end

FUNC FLIP_WORD
  '{$IFUSED FLIP_WORD}
  ASM
    MOV   __PARAM3, __PARAM1                    ' make copy to __WPARAM34
    MOV   __PARAM4, __PARAM2
    CLR   __PARAM5                              ' clear count

FW_Loop:
    RR    __PARAM4                              ' get bit from __WPARAM34
    RR    __PARAM3
    RL    __PARAM1                              ' move into __WPARAM12
    RL    __PARAM2
    INC   __PARAM5                              ' update count
    JNB   __PARAM5.4, @FW_Loop                  ' abort at 16
  ENDASM
  '{$ENDIF}
  ENDFUNC

Post Edited (JonnyMac) : 5/22/2009 12:56:56 AM GMT

How can I flip bits in SX/B?

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