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VREV8.V

RISC-V VREV8.V Instruction Details

Instruction ManualR-type

Vector byte-reverse: reverse byte order within each SEW element (endianness swap)

Instruction Syntax

vrev8.v vd, vs2, vm

Operand Breakdown

vd: destination vector register group.

vs2/vs1 or scalar source: selected by suffixes such as .vv, .vx, .vi, or .vf.

vm: when present, vm=0 uses v0 as the execution mask and vm=1 is unmasked.

ZvbbVector Bit Manipulation

Related Search Terms

vrev8.v instruction RISC-V vrev8.v vrev8.v syntax vrev8.v encoding Zvbb vector reverse bytes

Instruction Behavior

vrev8.v is the Zvbb vector byte-reverse instruction. Reverses byte order within each SEW element. E.g., for 32-bit: [b0,b1,b2,b3]→[b3,b2,b1,b0]. Commonly used for endianness conversion. Different from vbrev8.v (bit-reverse within bytes): vrev8 swaps byte positions, vbrev8 swaps bits within bytes.

Quick Understanding & Search Notes

VREV8.V is a Zvbb vector instruction for vector reverse bytes. This page is checked against the official vector crypto extension and V-extension execution model.

Reverses byte order within each SEW element without reversing bits inside bytes.

It follows V-extension vl, vstart, vtype, and optional vm mask rules.

RISC-V Unprivileged ISA Manual: Vector cryptography extensions 1.0 RISC-V Unprivileged ISA Manual: V standard vector extension

Vector Execution Context

When reading VREV8.V, do not stop at the mnemonic. Official V-extension semantics also depend on the current vl, vtype, and mask state. The suffix and operand form determine whether sources are vector, scalar, or immediate values.

Check vl first

The current vl determines the number of body elements. Typical code executes vsetvli, vsetivli, or vsetvl before this instruction.

Then check vtype

The current vtype supplies SEW, LMUL, tail policy, and mask policy; these affect element width, register-group size, and inactive/tail destination elements.

Then check vm/v0

For ordinary vector instructions with vm, vm=0 uses v0 as the execution mask and vm=1 is unmasked. A few forms such as VMERGE use v0 as data-selection input.

Official source: RISC-V V Standard Extension for Vector Operations

Common Usage Scenarios

Crypto & Security

Understand this scenario with real code like «vrev8.v vd, vs2».

Vector Acceleration

Understand this scenario with real code like «vrev8.v vd, vs2».

Pre-Use Checklist

Syntax Check

Confirm the current instruction format is R-type.
Confirm the operand order matches the example.

Semantic Check

Ensure the destination register usage is compatible with the calling convention.
Confirm this is not the lower-level form of a pseudo-instruction expansion.

Pitfalls / Common Confusions

Reverses byte order, not bit order within bytes. Orthogonal to vbrev8.v.

FAQ

Can VREV8.V always use a v0.t mask?

It can use the vm mask operand shown in the syntax; omitting it gives the unmasked form.

What determines the element width for VREV8.V?

The current vtype SEW determines it, subject to any instruction-specific SEW restrictions in the extension.