What is Movsx Assembly?
What is Movsx Assembly?
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 does XOR do in assembly?
The XOR instruction performs a bit wise Exclusive OR operation between corresponding bits in the two operands and places the result in the first operand. reg, mem, and immed can be 8, 16, or 32 bits. The XOR instruction can be used to reverse selected bits in an operand while preserving the remaining bits.
What is MOV instruction x86?
The mov instruction copies the data item referred to by its second operand (i.e. register contents, memory contents, or a constant value) into the location referred to by its first operand (i.e. a register or memory).
What is CDQ Assembly?
Description. The CDQ (Convert Doubleword to Quadword) instruction extends the sign bit of EAX into the EDX register.
What is je in assembly?
In assembly, all branching is done using two types of instruction: A conditional jump instruction, like “je” (jump-if-equal), does a goto somewhere if the two values satisfy the right condition. For example, if the values are equal, subtracting them results in zero, so “je” is the same as “jz”.
What does Lea do in assembly?
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 does not do in assembly?
NOT operation reverses the bits in an operand. The operand could be either in a register or in the memory.
What does Callq do in assembly?
The callq instruction takes one operand, the address of the function being called. It pushes the return address (current value of %rip , which is the next instruction after the call) onto the stack and then jumps to the address of the function being called.
Is INC faster than add?
ADD is not always faster than INC , but it is almost always at least as fast (there are a few corner cases on certain older micro-architectures, but they are exceedingly rare), and sometimes significantly faster. For more details, consult Intel’s Optimization Reference Manual or Agner Fog’s micro-architecture notes.
How does Div work in assembly?
div executes unsigned division. div divides a 16-, 32-, or 64-bit register value (dividend) by a register or memory byte, word, or long (divisor). The quotient is stored in the AL, AX, or EAX register respectively. The remainder is stored in AH, Dx, or EDX.
What does CDQ stand for?
CDQ
| Acronym | Definition |
|---|---|
| CDQ | Convert Doubleword to Quadword (Win32 assembly) |
| CDQ | Corporate Data Quality |
| CDQ | Client Diagnostic Questionnaire (Mental Health Screening Tool) |
| CDQ | Compact Disc Quality |
How do you jump in assembly?
Sr.No. This is performed by the JMP instruction….Conditional Jump.
| Instruction | Description | Flags tested |
|---|---|---|
| JNE/JNZ | Jump not Equal or Jump Not Zero | ZF |
| JA/JNBE | Jump Above or Jump Not Below/Equal | CF, ZF |
| JAE/JNB | Jump Above/Equal or Jump Not Below | CF |
| JB/JNAE | Jump Below or Jump Not Above/Equal | CF |
How does the assembly instruction MOVSX work?
How does the assembly instruction MOVSX work in this following example: From what I thought, it takes last bytes of [EDX] = 9F, moves it to ECX and then sign extends it to match 16 bits = 0000009F. However, the actual result is 00000016.
How to extend a value with MOVSX and movzx?
Sign Extending with MOVSX and MOVZX The 80386/486/Pentium processors provide instructions that move and extend a value to a larger data size in a single step. 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 .
Which is the special version of the MOV instruction?
In other words, it is used to read and write into memory. MOVSX (Move with sign extension) and MOVZX (Move with zero extension) are special versions of the mov instruction that perform sign extension or zero extension from the source to the destination. This is the only instruction that allows the source and destination to be different sizes.
Can you use movzx to move a byte?
For example, you could not use the MOV command to move a BYTE value into the EAX register because a BYTE is 8 bits and the EAX register is 32 bits. This is where MOVZX and MOVSX come into play. Using MOVZX, you could move a BYTE value into the EAX register.