Can VCLMULH.VX always use a v0.t mask?
It can use the vm mask operand shown in the syntax; omitting it gives the unmasked form.
VCLMULH.VX
RISC-V VCLMULH.VX Instruction Details
Instruction ManualR-typeVector-scalar carry-less multiply high: GF(2) multiply with broadcast rs1, high SEW bits
Instruction Syntax
vclmulh.vx vd, vs2, rs1, vm
Operand Breakdown
Destination rd: register receiving the operation result.
Source rs1: register holding the first operand.
Source rs2: register holding the second operand.
ZvbcVector CryptoBit Manipulation
Instruction Behavior
vclmulh.vx is the Zvbc vector-scalar carry-less multiply high. Broadcasts rs1, performs GF(2) multiply with vs2[i], returning high SEW bits. SEW=64.
Quick Understanding & Search Notes
VCLMULH.VX is a Zvbc vector instruction for vector-scalar carry-less multiply high. This page is checked against the official vector crypto extension and V-extension execution model.
The scalar and each element are carry-less multiplied, returning high SEW bits; SEW=64.
It follows V-extension vl, vstart, vtype, and optional vm mask rules.
Zvbc vclmul/vclmulh are defined only for SEW=64.
Common Usage Scenarios
Crypto & Security
Understand this scenario with real code like «vclmulh.vx vd, vs2, a1».
Vector Acceleration
Understand this scenario with real code like «vclmulh.vx vd, vs2, a1».
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
SEW=64. Returns high 64 bits.
FAQ
What determines the element width for VCLMULH.VX?
The current vtype SEW determines it, subject to any instruction-specific SEW restrictions in the extension.