来看看这个

FUNCTION "BIT_COUNT" : Int

TITLE = 'BIT_COUNT'

{ S7_Optimized_Access := 'FALSE' }

AUTHOR : hugo

FAMILY : GATE

NAME : BITCT

VERSION : 1.1

// Automatically Edited - Old code marked with //~ - (UTC) 10/2/2012 5:11:58 PM

//

//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.

   VAR_INPUT

      IN_DW : DWord;

   END_VAR

   VAR_TEMP

      temp : DWord;

      attemp AT temp : Array[0..31] of Bool;

   END_VAR

BEGIN

    #BIT_COUNT := 0;

    #temp := #IN_DW;

    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