4.1 Data transfer instructions
4.1.2 Operand Type
Operands are three basic types:
- Immediate - digital text expression
- Register operand - using the CPU registers named
- Memory operand - referenced memory location
| Number of operations | Explanation |
|---|---|
| reg8 | 8 general-purpose registers: AH, AL, BH, BL, CH, CL, DH, DL |
| Regl6 | 16-bit general purpose registers: AX, BX, CX, DX, SI, DI, SP, BP |
| reg32 | 32-bit general purpose registers: EAX, EEX, ECX, EDX, ESI, EDI, ESP, EBP |
| reg | General-purpose registers |
| comfortable | 16-bit segment register: CS, DS, SS, ES, FS, GS |
| imm | 8, 16-bit or 32-bit immediate data |
| imm8 | 8, immediate byte value |
| imm16 | 16, immediate word values |
| imm32 | 32-bit immediate data, double word value |
| reg/mem8 | 8 operand may be an 8-bit general purpose registers or memory byte |
| reg/mem16 | 16-bit immediate data may be a 16 bit general purpose register or a memory word |
| reg/mem32 | 32-bit immediate which can be 32-bit double word general register or memory |
| mem | 8, 16-bit or 32-bit memory operand |
Direct memory operand: variable name referenced is the offset within the data segment.
4.2 Addition and subtraction
4.2.4 NEG instruction
NEG: the digital conversion by the corresponding complementary codes to obtain its opposite number.
TITLE Add and Subtract INCLUDE Irvine32.inc ;计算26+(-25) .data Val SDWORD 25 .code main PROC mov eax,Val neg eax;-25 add eax,26 call DumpRegs INVOKE ExitProcess,0 main ENDP END main
4.3 and operators and data related directives
OFFSET operator returns the offset of the data label. This offset in bytes, it indicates the start address of the data from the reference distance data segment.
TITLE test INCLUDE Irvine32.inc .data Val SDWORD 25 Val1 SDWORD 66 .code main PROC mov esi,OFFSET Val mov edi,OFFSET Val1 mov eax,0 mov eax,[esi] call DumpRegs INVOKE ExitProcess,0 main ENDP END main
ALIGN directive to align a variable byte boundaries, word boundaries, or double word boundary paragraph boundary.
bVal BYTE ? ;00404000h ALIGN 2 wVal WORD ? ;00404002h bVal2 BYTE ? ;00404004h ALIGN 4 dVal DWORD ? ;00404008h dVal2 DWORD ? ;0040400Ch
PTR operator can be used to rewrite the operand has been declared a type size.
TITLE test INCLUDE Irvine32.inc .data Val SDWORD 12345678h .code main PROC mov eax,0 mov ax,WORD PTR Val;ax=5678h call DumpRegs INVOKE ExitProcess,0 main ENDP END main
TYPE operator returns a single element of variable size, the size in bytes of the calculation. For example, the TYPE byte, the return value is 1; TYPE word is, the return value is 2; TYPE double word, the return value is 4; TYPE quadword, the return value is 8.
Number, the number of elements LENGTHOF operator computing elements in the array is an array of numeral value appears in the same row defined.
LABEL directive may be inserted into a label, and the definition of its size attribute, but does not allocate storage for the reference.
.data val16 LABEL WORD val32 DWORD 12345678h .code mov ax,val16 ; AX = 5678h mov dx,[val16+2] ; DX = 1234h
4.4 Indirect Addressing
4.4.1 indirect operand
Protected Mode
Any 32-bit general purpose registers (EAX, EBX, ECX, EDX, ESI, EDI, EBP, and ESP) can constitute a parenthesize indirect operands.
Index operand
Indexing operand refers to adding a constant in the register to generate a valid address. Each 32-bit general purpose registers can be used as index registers. MASM can use different symbols to represent the indexed operation (brackets is a partial symbols):
16-bit register
In real-address mode, generally a 16-bit register as the indexed operation. In this case, the register can be used only SI, DI, BX and BP:
Indexed scale factor operation
In calculating the shift amount, index operand must consider the size of each array element. Such as the embodiment of the double word, the subscript (3) to be multiplied by 4 (a double word size) to generate content for the offset of the array elements 400h
4.4.4 Pointer
TITLE Test Program . Irvine32 the INCLUDE inc is ; create user-defined types PBYTE TYPEDEF the PTR BYTE PWORD TYPEDEF the PTR WORD PDWORD TYPEDEF the PTR DWORD .data Strl BYTE . 1 , 2 , . 3 Str2 in WORD . 4 , . 5 , . 6 Str3 starting DWORD . 7 , . 8 , . 9 ; Create pointer variable PTr1 PBYTE Strl ptr2 PWORD Str2 in ptr3 PDWORD Str3 .code main the PROC MOV ESI, PTr1 ; the value of the pointer variable assignment MOV EAX, 0 MOV al,[esi + TYPE Str1] mov eax,0 mov esi,ptr2 mov ax,[esi + TYPE Str2] mov eax,0 mov esi,ptr3 mov eax,[esi + TYPE Str3] call DumpRegs exit main ENDP END main
