Assembly language program to count number of 1's in binary number

Question

Can someone please help I stuck since few day on this problem. I want to count numbers of 1's in binary value of 2 decimal/hexa. But I am getting incorrect results. Here a code below:

.386  //32-bit processor
.model small, stdcall  
ExitProcess PROTO, deExitCode:DWORD  
.data  
var1 dw 2  
.code  
main PROC  
    LEA ESI,var1  
    MOV EBX, 4 //SIZE OF ARRAY AS 2 binary will be 0010  
    MOV ECX,0  
 L1:CMP EBX,0  
    JE L3  
    MOV EAX,[ESI]  
    CMP EAX,0  
    JE L2  
    INC ECX  
 L2:DEC EBX  
    ADD SI,2  
    JMP L1  
 L3: INVOKE ExitProcess,0  
main ENDP  
END main

[NASM: Count how many bits in a 32 Bit number are set to 1](https://stackoverflow.com/q/2931497) shows some efficient loops for doing this on 32 bits at a time. Use a `movzx` load to widen a 16 bit value. — Peter Cordes, Nov 27 '22 at 14:49

score 3 · Accepted Answer · answered Sep 30 '21 at 10:42

If I understand your weird terminology to count numbers of 1's in binary value, you want to count how many bits is set to 1 in a 16bit memory variable var1. A straightforward solution is to load the variable to a register (MOVZX EAX,[var1]) and then 16 times shift the lowest bit to CF (SHR EAX,1) and add the CF to a counter register (ADC ECX,0) each time.

However, your code seems to count how many of four words in memory has a nonzero value. There are some bugs in it:

SIZE OF ARRAY which you have statically defined as var1 is not 4. It would have to be defined as var1 DW 2,3,4,5 ; Array of four words.
MOV EAX,[ESI] correctly loads AX from var1 but it also loads whatever garbage follows var1 to upper 16 bits of EAX.
ADD SI,2 should be ADD ESI,2.

Assembly language program to count number of 1's in binary number

1 Answers1