asked on

PRINT OUT FLAGS REGISTER

This code will not print the flags register correctly. It appears that pushf and popf are getting a static set of bits...not the register flags in effect after the instruction. I have played around with push/pop and pushf/popf using a variety of sequences but I continue to get results that don't show changes to the flag register after instruction 1-9 is executed. Can someone tell me what is wrong with this code? Thank you.

BIOS_CALL EQU 21h
STRING_OUT_FN EQU 09h
CHAR_IN_FN EQU 01h
CHAR_OUT_FN EQU 02h
EXIT_TO_DOS_FN EQU 4Ch
.model small
.stack 100h
.DATA
CRLF             EQU 0Ah,0Dh
HEADER_STR      DB CRLF," AX (Binary) OF CF SF ZF PF"
            DB CRLF," ---------------- -- -- -- -- --$"

FLAG_STR      DB " "
      OF_Disp DB '0', " "
      CF_Disp DB '0', " "
      SF_Disp DB '0', " "
      ZF_Disp DB '0', " "
      PF_Disp DB '0',"$"

LINE_1_STR      DB CRLF,"1. MOV AX, 8000h $"
LINE_2_STR      DB CRLF,"2. ADD AX, 0FFFFh $"
LINE_3_STR      DB CRLF,"3. RCL AX, 1 $"
LINE_4_STR      DB CRLF,"4. AND AX, AFAFh $"
LINE_5_STR      DB CRLF,"5. CMP AX, 00FFh $"
LINE_6_STR      DB CRLF,"6. MOV CL, 9 $"
LINE_7_STR      DB CRLF,"7. ROR AX, CL $"
LINE_8_STR      DB CRLF,"8, MOV CL, 02 $"
LINE_9_STR      DB CRLF,"9, SAR AX, CL $"
END_PROG_STR      DB CRLF,CRLF, "END OF PROGRAM.",CRLF,"$"

.CODE

MAIN PROC
      mov AX,@DATA
      mov DS,AX
;print the header
      ;
      LEA      DX, HEADER_STR
      CALL      PRINT_STR

      ;
      ; Execute Line 1
      ;
      LEA      DX, LINE_1_STR
      CALL      PRINT_STR
      MOV      AX, 8000h
      CALL      PRINT_RESULT

      ;
      ; Execute Line 2
      ;
      LEA      DX, LINE_2_STR
      CALL      PRINT_STR
      ADD      AX, 0FFFFh
      CALL      PRINT_RESULT

      ; Execute Line 3
      ;
      LEA      DX, LINE_3_STR
      CALL      PRINT_STR
      RCL AX, 1
      CALL      PRINT_RESULT
      ; Execute Line 4
      ;
      LEA      DX, LINE_4_STR
      CALL      PRINT_STR
      AND AX, 0AFAFH
      CALL      PRINT_RESULT

; Execute Line 5
      ;
      LEA      DX, LINE_5_STR
      CALL      PRINT_STR
      CMP AX, 00FFH
      CALL      PRINT_RESULT
      ;
      ; Execute Line 6
      ;
      LEA      DX, LINE_6_STR
      CALL      PRINT_STR
      MOV CL, 9
      CALL      PRINT_RESULT


      ; Execute Line 7
      ;
      LEA      DX, LINE_7_STR
      CALL      PRINT_STR
      ROR AX, CL
      CALL      PRINT_RESULT

      ; Execute Line 8
      ;
      LEA      DX, LINE_8_STR
      CALL      PRINT_STR
      MOV CL , 2
      CALL      PRINT_RESULT

      ; Execute Line 9
      ;
      LEA      DX, LINE_9_STR
      CALL      PRINT_STR
      SAR AX, CL
      CALL      PRINT_RESULT

      ; Exit to DOS
      ;
      LEA      DX,END_PROG_STR
      CALL      PRINT_STR
      mov AH,EXIT_TO_DOS_FN
      int BIOS_CALL

MAIN ENDP

PRINT_STR PROC

      PUSH       AX      ; preserve AX
      PUSH      BX      ; preserve BX
      PUSH      CX      ; preserve CX
      PUSHF            ; preserve flags


      MOV      AH, STRING_OUT_FN
      int      BIOS_CALL

      POPF            ; Restore flags
      POP       CX      ; Restore CX
      POP       BX      ; Restore BX
      POP       AX      ; Restore AX
      RET

PRINT_STR ENDP

PRINT_RESULT PROC

      CALL      PRINT_AX_BIN
      CALL      PRINT_FLAGS

      RET

PRINT_RESULT ENDP

PRINT_AX_BIN PROC


      PUSHF
      PUSH AX
      PUSH BX
      PUSH CX

      MOV      CX, 16
      MOV BX, AX

BINARY_PRINT_LOOP:

      MOV DL,'0'
      ROL BX, 1

      JNC PRINT1
      MOV DL,'1'
      PRINT1:
      MOV      AH, CHAR_OUT_FN
      INT      BIOS_CALL

      LOOP      BINARY_PRINT_LOOP


      POP CX
      POP BX
      POP AX
      POPF
RET
PRINT_AX_BIN ENDP

PRINT_FLAGS PROC

      PUSH      AX
      PUSH      BX
      PUSH      CX
      PUSHF
      POP       BX

      MOV            CX,'10'

      Test_CF:
      TEST       BX,0001H
      JC            Test_PF
      MOV            CF_Disp,CH

      Test_PF:
      TEST      BX,0004H
      JP            TEST_ZF
      MOV            PF_Disp,CH

      Test_ZF:
      TEST      BX,0040H
      JZ            Test_SF
      MOV            ZF_Disp,CH

      Test_SF:
      TEST      BX,0080H
      JS            Test_OF
      MOV            SF_Disp,CH

      Test_OF:
      TEST      BX,0800H
      JO            Test_done
      MOV            OF_Disp,CH

Test_done:
PUSH BX
POPF
      POP CX
      POP      BX
      POP      AX

      LEA        DX,FLAG_STR
      CALL      PRINT_STR
      RET
PRINT_FLAGS ENDP

END MAIN

ASKER CERTIFIED SOLUTION

maques

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BrianGEFF719

@maques: The TEST instruction modifies: CF, OF, PF, SF, ZF
REF: http://www.cs.tut.fi/~siponen/upros/intel/instr/test.html

Now, why not use LAHF, it will be easier to test flags:

PUSH AX
LAHF
Test_CF:
TEST AH,1
JC Test_PF
MOV CF_Disp,CH

Test_PF:
TEST BX,0004H
JP TEST_ZF
MOV PF_Disp,CH

Test_ZF:
TEST BX,0040H
JZ Test_SF
MOV ZF_Disp,CH

Test_SF:
TEST BX,0080H
JS Test_OF
MOV SF_Disp,CH

Test_OF:
TEST BX,0800H
JO Test_done
MOV OF_Disp,CH

Test_done:
POP AX

BrianGEFF719

Sorry, I accidentally submitted too early.

BrianGEFF719

PUSH AX
LAHF //LOAD FLAGS INTO AH
Test_CF:
TEST AH,1h
JZ Test_PF
MOV CF_Disp,CH

Test_PF:
TEST AH,4H
JZ TEST_ZF
MOV PF_Disp,CH

Test_ZF:
TEST AH,20H
JZ Test_SF
MOV ZF_Disp,CH

Test_SF:
TEST AH,80H
JZ Test_done
MOV SF_Disp,CH

POP AX

maques

LAHF could be fine. However, the script originally had two major problems and I tried to change as less as possible...
Otherwise the whole thing could be rewritten a bit differently...

BrianGEFF719

Pushing the flags to the stack requires a pop from the stack (in my opinion an unnecessary step if you can load them directly into a register).

BrianGEFF719

Also, you should check your bitmasks, the zero flag should be AND 40h.

BrianGEFF719

dwiseman3, do you have any comments about our suggestions?

dwiseman3

ASKER

an appology,Brian, for not replying...I got waylayed on another project. Maques solved the biggest part of my problem. The initialization enabled me to output results that helped me work through the rest of the problem. Then, I moved on to another project. The finer corrections that you mention all appear to make sense, though.