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Counting 1's in 16 bit word

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Join Date: Nov 2008

Posts: 8

Reputation: laguna92651 is an unknown quantity at this point

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laguna92651 laguna92651 is offline

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Counting 1's in 16 bit word

Oct 20th, 2009

I am trying to count the number of 1's in a sixteen bit word for MC68HC12. The only way I can think of is to use 16 BITA instructions, one for each bit location, then increment a counter. I suspect there is a more elegant way to do this. Could someone share their ideas with me.

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Join Date: Jun 2009

Posts: 830

Reputation: wildgoose is a name known to all

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wildgoose

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Practically a Posting Shark

Oct 24th, 2009

I'm VERY VERY rusty on a 68HC12

 Help with Code Tags 
 Assembly Syntax (Toggle Plain Text) 
  ldy   #16 ;Loop 16 times
Loop:
  asld            ; Carry <- A <- B <- 0           MSB in carry
  psha
  ?                 ; a = Sum
  adda a,0     ; a=a+0+carry
  ?                 ; Sum = a
  pula
 
  dey 
  bne  $Loop
  ldy   #16 ;Loop 16 times
Loop:
  asld            ; Carry <- A <- B <- 0           MSB in carry
  psha
  ?                 ; a = Sum
  adda a,0     ; a=a+0+carry
  ?                 ; Sum = a
  pula

  dey 
  bne  $Loop

Or branch around if carry is set and then increment inx with x=bit count

 Help with Code Tags 
 Assembly Syntax (Toggle Plain Text) 
  ldy   #16 ;Loop 16 times
  ldx   #0
Loop:
 asld            ; Carry <- A <- B <- 0           MSB in carry
  bcc $L1      ; Jump if bit clear
 
  inx             ; 1 more bit
 
$L1:
  dey 
  bne  $Loop
  ldy   #16 ;Loop 16 times
  ldx   #0
Loop:
 asld            ; Carry <- A <- B <- 0           MSB in carry
  bcc $L1      ; Jump if bit clear

  inx             ; 1 more bit

$L1:
  dey 
  bne  $Loop