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Can somebody expain this assembly code?

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jayanth.devarayanadurga

jayanth.devarayanadurga

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Can somebody please explain this piece of assembly code?

Code ASM - [expand]
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CPU Disasm
Address   Hex dump               Command                                  Comments
0053D984  /$ /66:8338 00         CMP WORD PTR DS:[EAX],0                  
0053D988  |. |75 05              JNE SHORT 0053D98F
0053D98A  |. |66:FF00            INC WORD PTR DS:[EAX]
0053D98D  |.^\EB F5              JMP SHORT 0053D984
0053D98F  |> |66:8338 0F         CMP WORD PTR DS:[EAX],0F
0053D993  |. |75 05              JNE SHORT 0053D99A
0053D995  |. |66:FF08            DEC WORD PTR DS:[EAX]
0053D998  |.^\EB EA              JMP SHORT 0053D984
0053D99A  \>  C3                 RETN
 
 
MOVZX EAX,BX
0053DA8C  |.  B9 06000000        |MOV ECX,6
0053DA91  |.  33D2               |XOR EDX,EDX
0053DA93  |.  F7F1               |DIV ECX
0053DA95  |.  83FA 05            |CMP EDX,5                               ; Switch (cases 0..5, 7 exits)
0053DA98  |.  0F87 F9020000      |JA 0053DD97
0053DA9E  |.  FF2495 A5DA5300    |JMP DWORD PTR DS:[EDX*4+53DAA5]
0053DAA5  |.  BDDA5300           |DD 0053DABD
0053DAA9  |.  34DB5300           |DD 0053DB34
0053DAAD  |.  AEDB5300           |DD 0053DBAE
0053DAB1  |.  2EDC5300           |DD 0053DC2E
0053DAB5  |.  ABDC5300           |DD 0053DCAB
0053DAB9  |.  1CDD5300           |DD 0053DD1C
0053DABD  |>  8BC3               |MOV EAX,EBX                             ; Case 0 of switch 
0053DABF  |.  66:35 B200         |XOR AX,00B2
0053DAC3  |.  0FB696 DF000000    |MOVZX EDX,BYTE PTR DS:[ESI+0DF]
0053DACA  |.  66:33C2            |XOR AX,DX
0053DACD  |.  0FB656 6F          |MOVZX EDX,BYTE PTR DS:[ESI+6F]
0053DAD1  |.  66:03C2            |ADD AX,DX
0053DAD4  |.  0FB696 FF000000    |MOVZX EDX,BYTE PTR DS:[ESI+0FF]
0053DADB  |.  66:33C2            |XOR AX,DX
0053DADE  |.  66:83E0 0F         |AND AX,000F
0053DAE2  |.  66:8945 F2         |MOV WORD PTR SS:[LOCAL.4+2],AX
0053DAE6  |.  8BC3               |MOV EAX,EBX
0053DAE8  |.  66:35 B200         |XOR AX,00B2
0053DAEC  |.  0FB656 5F          |MOVZX EDX,BYTE PTR DS:[ESI+5F]
0053DAF0  |.  66:2BC2            |SUB AX,DX
0053DAF3  |.  0FB656 0F          |MOVZX EDX,BYTE PTR DS:[ESI+0F]
0053DAF7  |.  66:2BC2            |SUB AX,DX
0053DAFA  |.  0FB656 4F          |MOVZX EDX,BYTE PTR DS:[ESI+4F]
0053DAFE  |.  66:33C2            |XOR AX,DX
0053DB01  |.  66:83E0 0F         |AND AX,000F
0053DB05  |.  66:8945 F0         |MOV WORD PTR SS:[LOCAL.4],AX
0053DB09  |.  8BC3               |MOV EAX,EBX
0053DB0B  |.  66:35 B200         |XOR AX,00B2
0053DB0F  |.  0FB656 2F          |MOVZX EDX,BYTE PTR DS:[ESI+2F]
0053DB13  |.  66:03C2            |ADD AX,DX
0053DB16  |.  0FB696 8F000000    |MOVZX EDX,BYTE PTR DS:[ESI+8F]
0053DB1D  |.  66:33C2            |XOR AX,DX
0053DB20  |.  0FB656 7F          |MOVZX EDX,BYTE PTR DS:[ESI+7F]
0053DB24  |.  66:03C2            |ADD AX,DX
0053DB27  |.  66:83E0 0F         |AND AX,000F
0053DB2B  |.  66:8945 EE         |MOV WORD PTR SS:[LOCAL.5+2],AX
0053DB2F  |.  E9 63020000        |JMP 0053DD97
 
 
 
 
 
0053DD97  |>  8D45 EE            |LEA EAX,[LOCAL.5+2]                     ; Default case of switch 
0053DD9A  |.  E8 E5FBFFFF        |CALL 0053D984                           
0053DD9F  |.  8D45 F2            |LEA EAX,[LOCAL.4+2]
0053DDA2  |.  E8 DDFBFFFF        |CALL 0053D984                           
0053DDA7  |.  8D45 F0            |LEA EAX,[LOCAL.4]
0053DDAA  |.  E8 D5FBFFFF        |CALL 0053D984                           
0053DDAF  |.  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DDB3  |.  66:3B45 F0         |CMP AX,WORD PTR SS:[LOCAL.4]
0053DDB7  |.  75 43              |JNE SHORT 0053DDFC
0053DDB9  |.  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DDBD  |.  66:83F0 06         |XOR AX,0006
0053DDC1  |.  66:85C0            |TEST AX,AX
0053DDC4  |.  75 0E              |JNZ SHORT 0053DDD4
0053DDC6  |.  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DDCA  |.  66:83F0 04         |XOR AX,0004
0053DDCE  |.  66:8945 F0         |MOV WORD PTR SS:[LOCAL.4],AX
0053DDD2  |.  EB 28              |JMP SHORT 0053DDFC
0053DDD4  |>  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DDD8  |.  66:83F0 06         |XOR AX,0006
0053DDDC  |.  66:83F8 0F         |CMP AX,0F
0053DDE0  |.  75 0E              |JNE SHORT 0053DDF0
0053DDE2  |.  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DDE6  |.  66:83F0 04         |XOR AX,0004
0053DDEA  |.  66:8945 F0         |MOV WORD PTR SS:[LOCAL.4],AX
0053DDEE  |.  EB 0C              |JMP SHORT 0053DDFC
0053DDF0  |>  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DDF4  |.  66:83F0 06         |XOR AX,0006
0053DDF8  |.  66:8945 F0         |MOV WORD PTR SS:[LOCAL.4],AX
0053DDFC  |>  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DE00  |.  66:3B45 EE         |CMP AX,WORD PTR SS:[LOCAL.5+2]
0053DE04  |.  75 43              |JNE SHORT 0053DE49
0053DE06  |.  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DE0A  |.  66:83F0 03         |XOR AX,0003
0053DE0E  |.  66:85C0            |TEST AX,AX
0053DE11  |.  75 0E              |JNZ SHORT 0053DE21
0053DE13  |.  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DE17  |.  66:83F0 02         |XOR AX,0002
0053DE1B  |.  66:8945 EE         |MOV WORD PTR SS:[LOCAL.5+2],AX
0053DE1F  |.  EB 28              |JMP SHORT 0053DE49
0053DE21  |>  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DE25  |.  66:83F0 03         |XOR AX,0003
0053DE29  |.  66:83F8 0F         |CMP AX,0F
0053DE2D  |.  75 0E              |JNE SHORT 0053DE3D
0053DE2F  |.  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DE33  |.  66:83F0 02         |XOR AX,0002
0053DE37  |.  66:8945 EE         |MOV WORD PTR SS:[LOCAL.5+2],AX
0053DE3B  |.  EB 0C              |JMP SHORT 0053DE49
0053DE3D  |>  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DE41  |.  66:83F0 03         |XOR AX,0003
0053DE45  |.  66:8945 EE         |MOV WORD PTR SS:[LOCAL.5+2],AX
0053DE49  |>  0FB745 F0          |MOVZX EAX,WORD PTR SS:[LOCAL.4]
0053DE4D  |.  66:3B45 EE         |CMP AX,WORD PTR SS:[LOCAL.5+2]
0053DE51  |.  75 77              |JNE SHORT 0053DECA
0053DE53  |.  66:C745 EA 0200    |MOV WORD PTR SS:[LOCAL.6+2],2
0053DE59  |.  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DE5D  |.  66:3345 F0         |XOR AX,WORD PTR SS:[LOCAL.4]
0053DE61  |.  66:3B45 EA         |CMP AX,WORD PTR SS:[LOCAL.6+2]
0053DE65  |.  75 06              |JNE SHORT 0053DE6D
0053DE67  |.  66:C745 EA 0500    |MOV WORD PTR SS:[LOCAL.6+2],5
0053DE6D  |>  66:C745 EC 0700    |MOV WORD PTR SS:[LOCAL.5],7
0053DE73  |.  0FB745 F2          |MOVZX EAX,WORD PTR SS:[LOCAL.4+2]
0053DE77  |.  66:3345 F0         |XOR AX,WORD PTR SS:[LOCAL.4]
0053DE7B  |.  66:3B45 EC         |CMP AX,WORD PTR SS:[LOCAL.5]
0053DE7F  |.  75 06              |JNE SHORT 0053DE87
0053DE81  |.  66:C745 EC 0800    |MOV WORD PTR SS:[LOCAL.5],8
0053DE87  |>  0FB745 F0          |MOVZX EAX,WORD PTR SS:[LOCAL.4]
0053DE8B  |.  66:3345 EA         |XOR AX,WORD PTR SS:[LOCAL.6+2]
0053DE8F  |.  66:85C0            |TEST AX,AX
0053DE92  |.  75 0E              |JNZ SHORT 0053DEA2
0053DE94  |.  0FB745 F0          |MOVZX EAX,WORD PTR SS:[LOCAL.4]
0053DE98  |.  66:3345 EC         |XOR AX,WORD PTR SS:[LOCAL.5]
0053DE9C  |.  66:8945 EE         |MOV WORD PTR SS:[LOCAL.5+2],AX
0053DEA0  |.  EB 28              |JMP SHORT 0053DECA
0053DEA2  |>  0FB745 F0          |MOVZX EAX,WORD PTR SS:[LOCAL.4]
0053DEA6  |.  66:3345 EA         |XOR AX,WORD PTR SS:[LOCAL.6+2]
0053DEAA  |.  66:83F8 0F         |CMP AX,0F
0053DEAE  |.  75 0E              |JNE SHORT 0053DEBE
0053DEB0  |.  0FB745 F0          |MOVZX EAX,WORD PTR SS:[LOCAL.4]
0053DEB4  |.  66:3345 EC         |XOR AX,WORD PTR SS:[LOCAL.5]
0053DEB8  |.  66:8945 EE         |MOV WORD PTR SS:[LOCAL.5+2],AX
0053DEBC  |.  EB 0C              |JMP SHORT 0053DECA
0053DEBE  |>  0FB745 F0          |MOVZX EAX,WORD PTR SS:[LOCAL.4]
0053DEC2  |.  66:3345 EA         |XOR AX,WORD PTR SS:[LOCAL.6+2]
0053DEC6  |.  66:8945 EE         |MOV WORD PTR SS:[LOCAL.5+2],AX
0053DECA  |>  66:837D EE 00      |CMP WORD PTR SS:[LOCAL.5+2],0
0053DECF  |.  75 1D              |JNE SHORT 0053DEEE
0053DED1  |.  66:BF 0100         |MOV DI,1
0053DED5  |>  66:3B7D F0         |/CMP DI,WORD PTR SS:[LOCAL.4]
0053DED9  |.  74 0C              ||JE SHORT 0053DEE7
0053DEDB  |.  66:3B7D F2         ||CMP DI,WORD PTR SS:[LOCAL.4+2]
0053DEDF  |.  74 06              ||JE SHORT 0053DEE7
0053DEE1  |.  66:897D EE         ||MOV WORD PTR SS:[LOCAL.5+2],DI
0053DEE5  |.  EB 07              ||JMP SHORT 0053DEEE
0053DEE7  |>  47                 ||INC EDI
0053DEE8  |.  66:83FF 0F         ||CMP DI,0F
0053DEEC  |.^ 75 E7              |\JNE SHORT 0053DED5
0053DEEE  |>  66:837D EE 0F      |CMP WORD PTR SS:[LOCAL.5+2],0F
0053DEF3  |.  75 1D              |JNE SHORT 0053DF12
0053DEF5  |.  66:BF 0100         |MOV DI,1
0053DEF9  |>  66:3B7D F0         |/CMP DI,WORD PTR SS:[LOCAL.4]
0053DEFD  |.  74 0C              ||JE SHORT 0053DF0B
0053DEFF  |.  66:3B7D F2         ||CMP DI,WORD PTR SS:[LOCAL.4+2]
0053DF03  |.  74 06              ||JE SHORT 0053DF0B
0053DF05  |.  66:897D EE         ||MOV WORD PTR SS:[LOCAL.5+2],DI
0053DF09  |.  EB 07              ||JMP SHORT 0053DF12
0053DF0B  |>  47                 ||INC EDI
0053DF0C  |.  66:83FF 0F         ||CMP DI,0F
0053DF10  |.^ 75 E7              |\JNE SHORT 0053DEF9
0053DF12  |>  66:85DB            |TEST BX,BX
0053DF15  |.  0F86 C4000000      |JBE 0053DFDF
0053DF1B  |.  0FB7C3             |MOVZX EAX,BX
0053DF1E  |.  03C0               |ADD EAX,EAX
0053DF20  |.  0FB644C6 F1        |MOVZX EAX,BYTE PTR DS:[EAX*8+ESI-0F]
0053DF25  |.  0FB7D3             |MOVZX EDX,BX
0053DF28  |.  03D2               |ADD EDX,EDX
0053DF2A  |.  3244D6 F2          |XOR AL,BYTE PTR DS:[EDX*8+ESI-0E]
0053DF2E  |.  0FB6C0             |MOVZX EAX,AL
0053DF31  |.  0FB7D3             |MOVZX EDX,BX
0053DF34  |.  03D2               |ADD EDX,EDX
0053DF36  |.  0FB654D6 F3        |MOVZX EDX,BYTE PTR DS:[EDX*8+ESI-0D]
0053DF3B  |.  66:03C2            |ADD AX,DX
0053DF3E  |.  0FB7D3             |MOVZX EDX,BX
0053DF41  |.  03D2               |ADD EDX,EDX
0053DF43  |.  0FB654D6 F4        |MOVZX EDX,BYTE PTR DS:[EDX*8+ESI-0C]
0053DF48  |.  66:03C2            |ADD AX,DX
0053DF4B  |.  66:8945 F6         |MOV WORD PTR SS:[LOCAL.3+2],AX
0053DF4F  |.  0FB7C3             |MOVZX EAX,BX
0053DF52  |.  03C0               |ADD EAX,EAX
0053DF54  |.  0FB644C6 F5        |MOVZX EAX,BYTE PTR DS:[EAX*8+ESI-0B]
0053DF59  |.  66:0345 F6         |ADD AX,WORD PTR SS:[LOCAL.3+2]
0053DF5D  |.  0FB7D3             |MOVZX EDX,BX
0053DF60  |.  03D2               |ADD EDX,EDX
0053DF62  |.  0FB654D6 F6        |MOVZX EDX,BYTE PTR DS:[EDX*8+ESI-0A]
0053DF67  |.  66:03C2            |ADD AX,DX
0053DF6A  |.  0FB7D3             |MOVZX EDX,BX
0053DF6D  |.  03D2               |ADD EDX,EDX
0053DF6F  |.  0FB654D6 F7        |MOVZX EDX,BYTE PTR DS:[EDX*8+ESI-9]
0053DF74  |.  66:03C2            |ADD AX,DX
0053DF77  |.  0FB7D3             |MOVZX EDX,BX
0053DF7A  |.  03D2               |ADD EDX,EDX
0053DF7C  |.  0FB654D6 F8        |MOVZX EDX,BYTE PTR DS:[EDX*8+ESI-8]
0053DF81  |.  66:03C2            |ADD AX,DX
0053DF84  |.  66:8945 F6         |MOV WORD PTR SS:[LOCAL.3+2],AX
0053DF88  |.  0FB7C3             |MOVZX EAX,BX
0053DF8B  |.  03C0               |ADD EAX,EAX
0053DF8D  |.  0FB644C6 F9        |MOVZX EAX,BYTE PTR DS:[EAX*8+ESI-7]
0053DF92  |.  0FB7D3             |MOVZX EDX,BX
0053DF95  |.  03D2               |ADD EDX,EDX
0053DF97  |.  3244D6 FA          |XOR AL,BYTE PTR DS:[EDX*8+ESI-6]
0053DF9B  |.  0FB6C0             |MOVZX EAX,AL
0053DF9E  |.  66:0345 F6         |ADD AX,WORD PTR SS:[LOCAL.3+2]
0053DFA2  |.  0FB7D3             |MOVZX EDX,BX
0053DFA5  |.  03D2               |ADD EDX,EDX
0053DFA7  |.  0FB654D6 FB        |MOVZX EDX,BYTE PTR DS:[EDX*8+ESI-5]
0053DFAC  |.  66:03C2            |ADD AX,DX
0053DFAF  |.  0FB7D3             |MOVZX EDX,BX
0053DFB2  |.  03D2               |ADD EDX,EDX
0053DFB4  |.  0FB654D6 FC        |MOVZX EDX,BYTE PTR DS:[EDX*8+ESI-4]
0053DFB9  |.  66:03C2            |ADD AX,DX
0053DFBC  |.  66:8945 F6         |MOV WORD PTR SS:[LOCAL.3+2],AX
0053DFC0  |.  0FB7C3             |MOVZX EAX,BX
0053DFC3  |.  03C0               |ADD EAX,EAX
0053DFC5  |.  0FB644C6 FD        |MOVZX EAX,BYTE PTR DS:[EAX*8+ESI-3]
0053DFCA  |.  66:0345 F6         |ADD AX,WORD PTR SS:[LOCAL.3+2]
0053DFCE  |.  0FB7D3             |MOVZX EDX,BX
0053DFD1  |.  03D2               |ADD EDX,EDX
0053DFD3  |.  0FB654D6 FE        |MOVZX EDX,BYTE PTR DS:[EDX*8+ESI-2]
0053DFD8  |.  66:33C2            |XOR AX,DX
0053DFDB  |.  66:8945 F6         |MOV WORD PTR SS:[LOCAL.3+2],AX
0053DFDF  |>  0FB7C3             |MOVZX EAX,BX
0053DFE2  |.  03C0               |ADD EAX,EAX
0053DFE4  |.  8D04C6             |LEA EAX,[EAX*8+ESI]
0053DFE7  |.  0FB755 F2          |MOVZX EDX,WORD PTR SS:[LOCAL.4+2]
0053DFEB  |.  0FB60410           |MOVZX EAX,BYTE PTR DS:[EDX+EAX]
0053DFEF  |.  0FB7D3             |MOVZX EDX,BX
0053DFF2  |.  03D2               |ADD EDX,EDX
0053DFF4  |.  8B4D FC            |MOV ECX,DWORD PTR SS:[LOCAL.1]
0053DFF7  |.  880411             |MOV BYTE PTR DS:[EDX+ECX],AL
0053DFFA  |.  0FB7C3             |MOVZX EAX,BX
0053DFFD  |.  03C0               |ADD EAX,EAX
0053DFFF  |.  8D04C6             |LEA EAX,[EAX*8+ESI]
0053E002  |.  0FB755 F0          |MOVZX EDX,WORD PTR SS:[LOCAL.4]
0053E006  |.  0FB60410           |MOVZX EAX,BYTE PTR DS:[EDX+EAX]
0053E00A  |.  0FB7D3             |MOVZX EDX,BX
0053E00D  |.  03D2               |ADD EDX,EDX
0053E00F  |.  8B4D FC            |MOV ECX,DWORD PTR SS:[LOCAL.1]
0053E012  |.  884411 01          |MOV BYTE PTR DS:[EDX+ECX+1],AL
0053E016  |.  66:85DB            |TEST BX,BX
0053E019  |.  76 26              |JBE SHORT 0053E041
0053E01B  |.  0FB7C3             |MOVZX EAX,BX
0053E01E  |.  03C0               |ADD EAX,EAX
0053E020  |.  8D04C6             |LEA EAX,[EAX*8+ESI]
0053E023  |.  0FB755 EE          |MOVZX EDX,WORD PTR SS:[LOCAL.5+2]
0053E027  |.  0FB60410           |MOVZX EAX,BYTE PTR DS:[EDX+EAX]
0053E02B  |.  0FB755 F6          |MOVZX EDX,WORD PTR SS:[LOCAL.3+2]
0053E02F  |.  66:83E2 0F         |AND DX,000F
0053E033  |.  66:3BC2            |CMP AX,DX
0053E036  |.  74 09              |JE SHORT 0053E041
0053E038  |.  C745 F8 01000000   |MOV DWORD PTR SS:[LOCAL.2],1
0053E03F  |.  EB 10              |JMP SHORT 0053E051
0053E041  |>  43                 |INC EBX
0053E042  |.  66:83FB 10         |CMP BX,10
0053E046  |.^ 0F82 3DFAFFFF      \JB 0053DA89
0053E04C  |.  33C0               XOR EAX,EAX
0053E04E  |.  8945 F8            MOV DWORD PTR SS:[LOCAL.2],EAX
0053E051  |>  33C0               XOR EAX,EAX
0053E053  |.  5A                 POP EDX
0053E054  |.  59                 POP ECX
0053E055  |.  59                 POP ECX
0053E056  |.  64:8910            MOV DWORD PTR FS:[EAX],EDX
0053E059  |.  68 66E05300        PUSH 0053E066                            ; Entry point
0053E05E  \>  C3                 RETN                                     ; Jump to 53E066
0053E05F   $^ E9 206BECFF        JMP 00404B84                             ; SE handling routine
0053E064   .^ EB F8              JMP SHORT 0053E05E
0053E066  />  8B45 F8            MOV EAX,DWORD PTR SS:[LOCAL.2]
0053E069  |.  5F                 POP EDI
0053E06A  |.  5E                 POP ESI
0053E06B  |.  5B                 POP EBX
0053E06C  |.  8BE5               MOV ESP,EBP
0053E06E  |.  5D                 POP EBP
0053E06F  \.  C3                 RETN
 
Last edited by a moderator:

This looks like a section of diusassembled code taken from a program written in 'C'. Without knowing at which address variables, contants and other routines are stored and the segment addresses, it isn't possible to explain its operation fully. The best you will manage is to use the processor's data sheet to see what each instruction does.

Brian.
 

I know most of the instructions. I want to know how the following instructions work.

Code ASM - [expand]
1
2
3

MOVZX EDX,BYTE PTR DS:[ESI+4F]
LEA EAX,[LOCAL.5+2]
CMP WORD PTR DS:[EAX],0


Let us assume ESI, LOCAL.5 contains memory address in the first 2 instructions. If address is 00556677 and 00556688 then in the first instruction ESI+4F becomes 00556677+4F = 005566C6. Then the value contained at address 005566C6 in DS is moved to EDX.

In the second instruction if LOCAL.5 variable in the stack contains the address 00556688 then 00556688+2 = 0055668A is loaded into EAX i.e., the address is loaded into EAX.

In the third instruction, if EAX contains the address 00556699 then 0 is compared with the value at address 00556699.

Am I right? If not, explain it.
 
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I think you are correct but the effective address of [LOCAL.5+2] is loaded into EAX so the third line compares the contents of 0055668A with zero. (assuming the data segment is the same)

To be honest, it's many years since I programmed x386 so I could be wrong.

Brian.
 

Actually I have taken the 3 instruction from different part of a routine. So, I want to know in the third instruction content of the memory location contained by or pointed to by EAX is compared with 0. Am I right?
 
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