16.2. BIT_COUNT

Type Function: INT

Input IN: DWORD (input)

Output INT (number of bits which have value TRUE (1) in IN)

BIT_COUNT determines the number of bits in IN, which have the value TRUE

FUNCTION BIT_COUNT : INT
TITLE = 'BIT_COUNT'
//
//BIT_COUNT counts the amount True of bits in a dword.
//for exabple: bit_count(3) returns 2 because two bits (bits 0 and 1) are true and all others are false.
//
VERSION : 1.1
AUTHOR : hugo
NAME : BITCT
FAMILY : GATE

VAR_INPUT
IN : DWORD;
END_VAR
VAR_TEMP
temp: DWORD;
attemp AT temp : ARRAY[0..31] OF BOOL;
END_VAR

BEGIN

Bit_Count := 0;
temp := in;

WHILE DWORD_TO_DINT(temp) <> 0 DO
IF attemp[24] THEN Bit_Count := Bit_Count +1; END_IF;
temp := SHR(IN:=temp,N:=1);
END_WHILE;

(* revision history
5.7.2007 rev 1.0 original version

10.9.2007 rev 1.1 hm
changed algorithm for better performace
the execution time has reduced by a factor of 5
deleted unused variable temp
*)
END_FUNCTION

Why an FB?  What memory or multi-instance capability is required?

Here's the above FC code (without all the comments) as well as an algorithm that skips all 0 bits (meaning if there is just 1 set bit, it only runs through the loop one time!):

'----------------
' DWORD Bit Count, works with BYTE, WORD, and DWORD inputs
'----------------
FUNCTION BIT_COUNT : INT
INPUT
  IN : DWORD;

TEMP
  temp: DWORD;
  attemp AT temp : ARRAY[0..31] OF BOOL;

BEGIN
  BIT_COUNT := 0;
  #temp := #in;

  WHILE DWORD_TO_DINT(#temp) <> 0 DO
    IF #attemp[24] THEN BIT_COUNT += 1; END_IF;
    #temp := SHR(IN:=#temp,N:=1);
  END_WHILE;

END_FUNCTION 

'------------------------------------------
' Bit Count using Brian Kernighan's method
' Brian Kernighan’s Algorithm to count set bits in an integer
'------------------------------------------

FUNCTION BIT_COUNT : DINT
INPUT
  IN : DINT;

TEMP
  temp : DINT;
  count: INT;

BEGIN
  #temp := #IN;
  #count := 0;

  WHILE (#temp) <> 0 DO  // skips all the 0 bits
    #temp = #temp AND (#temp - 1);  // clear the LSB set
    #count += 1;
  END_WHILE;

  BIT_COUNT := count;
END_FUNCTION

Kev

I've just created the following which is working in a Function and also works when adapted for a FB, adjust as required for different quantity of bits.

I created in ladder so I'll try and explain.

MOVE 0 to MW1000

if bit ? is on ADD 1 to MW1000

If bit ? is on ADD to MW1000

if bit ? is on ADD to MW1000

Keep going up to 16

MW1000 will tell you how many bits are on.

Replace ? with any bit address and replace MW1000 with anything more suitable for your application.