Check vl first
The current vl determines the number of body elements. Typical code executes vsetvli, vsetivli, or vsetvl before this instruction.
VGHSH.VV
RISC-V VGHSH.VV Instruction Details
Instruction ManualR-typeVector GHASH add-multiply: update partial hash in vd using ciphertext vs1 and hash subkey vs2.
Instruction Syntax
vghsh.vv vd, vs2, vs1
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.
ZvkgVector CryptoGCM/GHASH
Instruction Behavior
vghsh.vv performs a GHASH add-multiply over 128-bit element groups with SEW=32. It reads partial hash Y_i from vd, ciphertext X_i from vs1, hash subkey H from vs2, and writes updated partial hash Y_{i+1} to vd.
Quick Understanding & Search Notes
VGHSH.VV is a Zvkg vector instruction for vector GHASH add-multiply. This page is checked against the official vector crypto extension and V-extension execution model.
Performs the GHASH (Y_i + X_i) * H update over 128-bit element groups with SEW=32.
This element-group crypto instruction has no vm mask operand and executes at element-group granularity.
SEW=32, EGW=128, EGS=4; vl and vstart must be multiples of 4, and LMUL*VLEN must hold at least one element group.
Vector Execution Context
When reading VGHSH.VV, do not stop at the mnemonic. Official V-extension semantics also depend on the current vl, vtype, and mask state. .vv: two vector sources participate element by element.
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.
Common Usage Scenarios
Crypto & Security
Understand this scenario with real code like «vghsh.vv vd, vs2, vs1».
Vector Acceleration
Understand this scenario with real code like «vghsh.vv vd, vs2, vs1».
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
No vm operand; this element-group crypto instruction is not maskable.
Requires SEW=32, EGW=128. Operates on 128-bit group granularity.
GHASH uses a special polynomial in GF(2^128), not ordinary integer arithmetic.
SEW=32, EGW=128, EGS=4; vl and vstart must be multiples of 4, and LMUL*VLEN must be at least 128.
FAQ
Can VGHSH.VV always use a v0.t mask?
No. This element-group crypto instruction has no vm operand; ordinary RVV mask syntax should not be added to examples.
What determines the element width for VGHSH.VV?
This instruction fixes SEW=32 and executes on 128-bit element groups; other SEW values are reserved/illegal cases.