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How does SHL work in assembly?
The SHL (shift left) instruction performs a logical left shift on the destination operand, filling the lowest bit with 0. The SHR (shift right) instruction performs a logical right shift on the destination operand. The highest bit position is filled with a zero.
What is SHR in x86?
The shr or sar instruction is used to shift the bits of the operand destination to the right, by the number of bits specified in the count operand. Bits shifted beyond the destination are first shifted into the CF flag.
What is the purpose of rotate instruction?
The Rotate instruction is used to rotating the bits of accumulator. Applications of ROTATE Instructions: The ROTATE instructions are primarily used in arithmetic multiply and divide operations and for serial data transfer.
What is the difference between SHR and SAR instructions?
SAR and SHR shift the bits of the operand downward. The low-order bit is shifted into the carry flag. 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.
How does rotate right work?
Rotate Right (ror) The right rotate instruction shifts all bits in the register or memory operand specified. The least significant bit is rotated to the carry flag, the carry flag is rotated to the most significant bit position, all other bits are shifted to the right.
What does Sall do in assembly?
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 purpose of the SHR instruction?
The shr or sar instruction is used to shift the bits of the operand destination to the right, by the number of bits specified in the count operand.
When do you use Rol instead of SHL?
Before the 80386 (and opcode BT), ROL would be used a lot to test a bit (SHL doesn’t propagate to the carry flag) – actually in 8088, ROR/ROL would only shift by 1 bit at a time !!!! Also if you want to shift one way and then the other way without loosing the bits that have been shifted out of scope, you’d use ROR/ROL instead of SHR/SHL
What’s the difference between a SHL and a ROR?
SHL throws the high bit away and fills the low bit position with zero. ROR ROL are “historic” but still useful in a number of ways. Before the 80386 (and opcode BT), ROL would be used a lot to test a bit (SHL doesn’t propagate to the carry flag) – actually in 8088, ROR/ROL would only shift by 1 bit at a time !!!!
What’s the purpose of the rotate instructions in Assembly?
Rotates are required for bit shifts across multiple words. When you SHL the lower word, the high-order bit spills out into the carry. To complete the operation, you need to shift the higher word (s) while bringing in the carry to the low-order bit. RCL is the instruction that accomplishes this.