Description. movsx reads the contents of the register or effective address as a word or byte. movsx then sign-extends the 16- or 32-bit value to the operand-size attribute of the instruction. The result is stored in the destination register by movsx.
What is Movzx and Movsx?
MOVSX moves a signed value into a register and sign-extends it with 1. MOVZX moves an unsigned value into a register and zero-extends it with zero.
What is mov al?
MOV AL,[BL+SI] , Copy from RAM into AL. The RAM address is located at BL+SI. MOV [BL+SI],AL , Copy from AL into RAM. … It holds the start address of a data table. SI is the “source index”.
What is the AL register?
The least significant byte of AX can be used as a single 8-bit register called AL, while the most significant byte of AX can be used as a single 8-bit register called AH. These names refer to the same physical register. When a two-byte quantity is placed into DX, the update affects the value of DH, DL, and EDX.
What is Ja Assembly?
JA is used for jumping if the last “flag changing” instruction was on unsigned numbers. but on the other hand, JG is used for jumping if the last “flag changing” instruction was on signed numbers.
What does Movsx mean in assembly?
Move With Sign Extend (movsx)
What is Lea Assembly?
lea — Load effective address. The lea instruction places the address specified by its first operand into the register specified by its second operand. Note, the contents of the memory location are not loaded, only the effective address is computed and placed into the register.
What are register operands?
Register operands refer to data stored in registers. The following examples show typical register operands: mov bx, 10 , Load constant to BX add ax, bx , Add BX to AX jmp di , Jump to the address in DI. An offset stored in a base or index register often serves as a pointer into memory.
What does mov AX BX do?
MOV AX, BX , moves contents of register BX to register AX.
What is wrong with mov DS SS instruction?
The MOV ds,ss instruction is wrong because segment to segment transfer is not allowed.
What is EDX register used for?
The EAX, EBX, ECX, EDX, EBP, EDI, and ESI registers are all 32-bit general-purpose registers, used for temporary data storage and memory access. Some of CPU instructions modify specific registers.
What is SS register?
The stack segment register (SS) is usually used to store information about the memory segment that stores the call stack of currently executed program. SP points to current stack top. By default, the stack grows downward in memory, so newer values are placed at lower memory addresses.
What is Al and AX?
AX is the 16 lower bits of EAX. AH is the 8 high bits of AX (i.e. the bits 8-15 of EAX) and AL is the least significant byte (bits 0-7) of EAX as well as AX.
What does Jae mean in assembly?
jae means Jump if above or equal. It will jump if the carry flag is equal to 0.
What is SHL in assembly language?
The SHL (shift left) instruction performs a logical left shift on the destination operand, filling the lowest bit with 0.
What is Cmpl in x86?
Purpose. Compares the contents of two general-purpose registers logically. Syntax.
What does test EAX EAX do?
eax contains the return value of strcmp. test is like bitwise and except it only sets the flags. Anding a value with itself gives the same value, so test eax, eax sets the flags based on whatever eax contains. ZF is set when the result of an operation is zero.
What is neg in assembly?
Description. Replace the value of the byte, word, or long with its two’s complement, that is, neg subtracts the byte, word, or long value from 0, and puts the result in the byte, word, or long respectively. neg sets the carry flag to 1, unless initial value of the byte, word, or long is 0.
What is byte ptr?
byte ptr ->, it simply means that you want to fetch a byte from the address. if it said word ptr or dword ptr , you would get a word or dword from the address in source index.
What is the difference between Lea and MOV?
LEA stands for Load Effective Address. It takes the result from address generation, and puts that result directly in a register, without accessing memory. MOV , on the other hand, will move data to or from memory at the computed offset.
What is CLD in assembly language?
CLD: clear direction flag so that string pointers auto increment after each string operation. STD: std is used to set the direction flag to a 1 so that SI and/or DI will automatically be decremented to point to the next string element when one of the string instruction executes.
What does mov ah 4CH mean?
MOV AH, 4CH means store (or “move”) the hexadecimal value 4C into register AH .
What are the types of operand?
Types of Operands in Computer Organization
- Logical data.
What is source operand?
For instructions with two operands, the first (lefthand) operand is the source operand, and the second (righthand) operand is the destination operand (that is, source->,destination). … Memory operands are specified either by the name of a variable or by a register that contains the address of a variable.
What are the three basic types of operands?
Operands can be immediate (that is, constant expressions that evaluate to an inline value), register (a value in the processor number registers), or memory (a value stored in memory). An indirect operand contains the address of the actual operand value.
What are the limitations of MOV?
The MOV instruction has a few limitations: an immediate value cannot be moved into a segment register directly (i.e. mov ds,10) segment registers cannot be copied directly (i.e. mov es,ds) a memory location cannot be copied into another memory location (i.e. mov aNumber,aDigit)
What is MOV AX @data?
Mov ax,@data is way of loading starting address of data segment in ax. then by using mov ds,ax data segment gets initialized. this instruction is used in tasm assembler.
Is MOV AX BX possible?
In this case the instruction MOV [AX], BX would do the job, not MOV AX, [BX] : This instruction does more or less the opposite of MOV AX, [BX] : It writes data to memory. This time, the data in the register BX is written to the memory specified by the registers DS and AX .
Is MOV CS ax valid?
MOV CS, AX , Not allowed (Code segment register is never used as destination). Note: The following must be observed in 8086 instructions: 1. Never mix an 8-bit register with 16-bit, it is not allowed in microprocessor.
Which one is not a valid register?
Explanation: MAR or the memory address register is not a visible register. This register is user inaccessible. It contains the address of the memory block to be read or written to.
What is immediate and direct addressing?
In immediate addressing, the instruction itself contains the value to be used. … In direct addressing, the instruction tells where the value can be found, but the value itself is out in memory. In a high level language, direct addressing is frequently used for things like global variables.
What are 32-bit registers?
In computer architecture, 32-bit integers, memory addresses, or other data units are those that are 32 bits (4 octets) wide. Also, 32-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers, address buses, or data buses of that size.
What are types of registers?
Types of Register in Computer Organization
- AC ( accumulator )
- DR ( Data registers )
- AR ( Address registers )
- PC ( Program counter )
- MDR ( Memory data registers )
- IR ( index registers )
- MBR ( Memory buffer registers )
What is each register used for?
To speed up the processor operations, the processor includes some internal memory storage locations, called registers. The registers store data elements for processing without having to access the memory. A limited number of registers are built into the processor chip.
What is DX register?
DX register is the data register. It is usually for reserving data value. The registers CS, DS, ES, and SS are called segment registers. You may not fiddle with these registers. You can only use them in the correct ways only.
What is BX register?
BX – This is the base register. It is of 16 bits and is divided into two 8-bit registers BH and BL to also perform 8-bit instructions. It is used to store the value of the offset.
What is EBP register?
A frame pointer (the ebp register on intel x86 architectures, rbp on 64-bit architectures) contains the base address of the function’s frame. The code to access local variables within a function is generated in terms of offsets to the frame pointer.
What is indexed register?
An index register is a circuit that receives, stores, and outputs instruction-changing codes in a computer. This circuit is also called an address register or a register of modifications. A register is a data-holding place in a computer processor.
What does Jae stand for?
|JAE||Journal of Accounting and Economics (Elsevier publication)|
|JAE||Journal of Aesthetic Education|
|JAE||Japan Action Enterprise (stunt group)|
|JAE||Jump If Above or Equal|
What is the full meaning of Jae?
JAE – Junior Account Executive.
What is Jge Assembly?
jge means “Jump if greater or equal (SF=OF)“, it’s synonymous with jnl . See Intel x86 JUMP quick reference.
What is difference between SHR and SAR?
SAR and SHR shift the bits of the operand downward. … The effect is to divide the operand by 2. SAR performs a signed divide with rounding toward negative infinity (not the same as IDIV), the high-order bit remains the same. SHR performs an unsigned divide, the high-order bit is set to 0.
What is SHL x86?
The shl or sal instruction is used to shift the bits of the operand destination to the left, by the number of bits specified in the count operand. Bits shifted beyond the destination are first shifted into the CF flag. Zeros fill vacated positions during the shift operation.
What is the difference between SAL and SHL?
According to this, they are the same: The shift arithmetic left (SAL) and shift logical left (SHL) instructions perform the same operation, they shift the bits in the destination operand to the left (toward more significant bit locations).