What does Rep Movsb do in assembly?

In short, rep repeats the following string operation ecx times. movs copies data from ds:esi to es:edi and increments or decrements the pointers based on the setting of the direction flag. As such, repeating it will move a range of memory to somewhere else.

What is fast short Rep Movsb?

Fast Short REP MOV (FSRM) It was intended for strings of 128 bytes and less to also be quick, but, in fact, strings before 64 bytes are still slower with rep movsb than with, for example, simple 64-bit register copy. Besides that, FSRM is only implemented under 64-bit, not under 32-bit.

What is Assembly rep?

Description. Use the rep (repeat while equal), repnz (repeat while nonzero) or repz (repeat while zero) prefixes in conjunction with string operations. Each prefix causes the associated string instruction to repeat until the count register (CX) or the zero flag (ZF) matches a tested condition.

Which is the format for the instruction Movsb?

Instruction Description
MOVSB ES:[DI]<-DS[SI] ; IF (DF=0) {SI=SI+1; DI=DI+1} ELSE {SI=SI-1;DI=DI-1}
MOVSW ES:[DI+1:DI]<-DS[SI+1:SI] ; IF (DF=0) {SI=SI+2; DI=DI+2} ELSE {SI=SI-2;DI=DI-2}
MOVSD ES:[DI+3:DI]<-DS[SI+3:SI] ; IF (DF=0) {SI=SI+4; DI=DI+4} ELSE {SI=SI-4;DI=DI-4}

What is the difference between MOV and MOVS?

Operation. The MOV instruction copies the value of Rm into Rd . The MOVS instruction performs the same operation as the MOV instruction, but also updates the N and Z flags. The MVNS instruction takes the value of Rm , performs a bitwise logical negate operation on the value, and places the result into Rd .

What does assembly language uses?

Assembly language uses a mnemonic to represent, e.g., each low-level machine instruction or opcode, each directive, typically also each architectural register, flag, etc. Some of the mnemonics may be built in and some user defined. Many operations require one or more operands in order to form a complete instruction.

What is repeat in assembly language?

Ayesha Naeem. A loop is a block of statements that are repeatedly executed until a condition is satisfied. The assembly language uses JMP instruction to implement loops. However, the processor set can use the LOOP instruction to implement loops conveniently.

What is 4ch in assembly language?

mov ah,4ch is the first line of assembler code. The value 4C in hexadecimal is stored in the register AH. int 21h is the second line of assembler code. The software interrupt 21h is called. This interrupt, when given the value of 4ch in AH (as is the case here), causes the program to exit immediately.

What is MOVS instruction in arm?

The MOVS instruction is used to copy a data item (byte, word or doubleword) from the source string to the destination string. The source string is pointed by DS:SI and the destination string is pointed by ES:DI.

What is the difference between instruction MOVS and LDR?

The ADR instruction is mainly used to generate address-independent code, and it is not necessary to judge whether a number is an immediate number; the role of the LDR pseudo-instruction is that the subsequent data may not be an immediate number; while the MOV instruction is followed by a value, it can only be an …