Move seperate bytes into a word

[Darrel Taylor]

Here's one that won't get used.
But since the questions of how big and how fast came up, you won't find anything smaller or faster. (unless Bruce shows up)

GroupVars  VAR BYTE[6]
  A    VAR GroupVars(0)
  B    VAR GroupVars(1)
  C    VAR GroupVars(2)
  D    VAR GroupVars(3)
  ZW   VAR WORD EXT : @ZW = _GroupVars + 4

ASM
    CHK?RP _GroupVars
    swapf  _D, W     ; swap nibbles in D
    iorwf  _C, W     ; or with C
    movwf  ZW + 1    ; move to Highbyte of word
    swapf  _B, W     ; swap nibbles in B
    iorwf  _A, W     ; or with A
    movwf  ZW        ; move to LowByte of word
ENDASM

[mister_e]

yeah, no complaint at all, ASM route is easy & fast, but the only minor problem it use a bit more of RAM?

Who cares anyway

[Darrel Taylor]

Technically, it uses less RAM.

A statement like z=a+b<<4+c<<8+d<<12

Will create 3 T variables to hold the intermediate results.
Each T var is a Word (Long for PBPL), so it uses at least 6 more bytes of RAM.
Of course, if the program already had T vars from other statements, it won't make any difference.

For Flash, it uses 6-8 words depending on variable locations.
z=a+b<<4+c<<8+d<<12, uses ~60 depending on library routines already used.

And Time wise, it takes about 6-8 uS @ 4Mhz
z=a+b<<4+c<<8+d<<12, uses several hundred.
<br>

[Ioannis]

OK, that was not fair Darrel!

Cannot beat ASM code of course.

If I wanted to do that way, how can one find what this CHK?RP does? Where does this come from? I suppose there is no RTFM on this. Maybe digging deep inside PBP's librarys?

Ioannis

[Bruce]

OK - here's a little smaller verion...;o}

Z VAR WORD BANK0 ; use BANKA for 18F part
A VAR Z.LowByte
B VAR BYTE BANK0
C VAR Z.HighByte
D VAR BYTE BANK0

A=%00000001
B=%00000010
C=%00000011
D=%00000100

ASM
    CHK?RP _Z
    swapf  _B, W     ; swap nibbles in B, result in W
    iorwf  _A, F     ; or with A, result in A (low byte is done)
    swapf  _D, W     ; swap nibbles in D, result in W
    iorwf  _C, F     ; or with C, result in C (HighByte is done)
ENDASM

Z = %0100 0011 0010 0001

[Jerson]

Wow! What compact and fast code! Both Bruce and DT must have been coding in Assembler for ages to have such skill I might have coded it like Steve(mister_e) here and just got the job done. But, I guess, this is how compiler writers optimize their code generation capabilities. I would like to hazard a thought that this kind of optimisations would help PBP generate tighter code.

[Darrel Taylor]

That's why we don't have optimization contests for money around here...

Bruce would always win.

SWEET!<hr>

Ioannis,

The CHK?RP macro just changes the bank to where the specified variable is located. That way you don't have to keep track of where everything is. You can let PBP handle the banking, even though it's ASM.

And yup, wading through the library is about the only RTFM.
It's in the PBPPIC14.lib file for the 12F and 16F's.