Can VBREV8.V always use a v0.t mask?
It can use the vm mask operand shown in the syntax; omitting it gives the unmasked form.
VBREV8.V
RISC-V VBREV8.V Instruction Details
Instruction ManualR-typeVector bit-reverse within bytes: reverse bits in each byte, byte order preserved
Instruction Syntax
vbrev8.v vd, vs2, vm
Operand Breakdown
Destination rd: register receiving the operation result.
Source rs1: register holding the first operand.
Source rs2: register holding the second operand.
ZvbbVector Bit Manipulation
Instruction Behavior
vbrev8.v is the Zvbb vector byte-internal bit-reverse. Groups each element into bytes, reverses bits within each byte (bit[0]↔bit[7], etc.), preserving byte order. Distinct from vbrev.v (full element reverse).
Quick Understanding & Search Notes
VBREV8.V is a Zvbb vector instruction for vector reverse bits in bytes. This page is checked against the official vector crypto extension and V-extension execution model.
Reverses bit order within each byte only; byte positions do not change.
It follows V-extension vl, vstart, vtype, and optional vm mask rules.
Common Usage Scenarios
Crypto & Security
Understand this scenario with real code like «vbrev8.v vd, vs2».
Vector Acceleration
Understand this scenario with real code like «vbrev8.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 within each byte only; byte order unchanged. Use vbrev.v for full element reverse.
FAQ
What determines the element width for VBREV8.V?
The current vtype SEW determines it, subject to any instruction-specific SEW restrictions in the extension.