Mark Rages wrote:
> Here's a design challenge for you guys:
> 
> I have values in three file registers:  fileA, fileB, fileC.
> 
> I want to choose the value that's in the middle (numerically) and put it into W.


   movf  fileB,W
   subwf fileA,W  ; W=A-B
   movf  fileB,W  ; assume B is larger
   skpnc          ; if Carry is clear then B is larger
    movf fileA,W  ; carry is set, so A is larger (or equal)

   movwf temp     ;temp = max(A,B)

   subwf fileC,W  ; compare C, W = C-max(A,B)
   movf  temp,W   ; assume max(A,B) > C
   skpnc          ;
    movf fileC,W  ; C is larger than the max(A,B)

   ; W = max(A,B,C)

If you don't want to use a temp then:

   movf  fileB,W
   subwf fileA,W  ; W=B-A
   movf  fileB,W  ; assume B is larger
   skpnc          ; if Carry is clear then B is larger
    movf fileA,W  ; carry is set, so A is larger

   subwf fileC,W  ; compare C
   skpnc          ;
    movf fileC,W  ; C is larger than the max(A,B)
   skpc
    subwf fileC,W ; W = C - (C-max(A,B)) = max(A,B)

   ; W = max(A,B,C)



If you can trash the registers, you can write:

   movf  fileB,W
   subwf fileA,F
   skpnc
    movf fileA,W

   subwf fileC,F
   skpnc
    movf fileC,W

This is of course untested and probably has bugs... but I believe the 
approach works okay.

Scott
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