Does SHA512SIG0H use floating-point or vector registers?
No. These scalar crypto extension instructions use integer X registers.
SHA512SIG0H
RISC-V SHA512SIG0H Instruction Details
Instruction ManualR-typeHigh 32 bits of SHA-512 σ0 (RV32): compute σ0 from 64-bit input (rs1=hi, rs2=lo) and return bits[63:32]
Instruction Syntax
sha512sig0h rd, rs1, rs2
Operand Breakdown
Destination rd: register receiving the operation result.
Source rs1: register holding the first operand.
Source rs2: register holding the second operand.
ZknhCrypto & Security
Instruction Behavior
sha512sig0h is the Zknh SHA-512 σ0 high-half instruction (RV32 only). Concatenates rs1 (upper 32 bits) and rs2 (lower 32 bits) as a 64-bit input, computes σ0(x) = ROTR(x, 1) ^ ROTR(x, 8) ^ SHR(x, 7), and returns bits[63:32] to rd. Paired with sha512sig0l for full 64-bit SHA-512 σ0 on RV32.
SHA512SIG0H Decode And Execute Animation
Applies the official RV32 formula for one SHA-512 Sigma result word.
rd
rs1
rs2
sha512sig0h
,
,
Execution Context
XLEN is fixed at 32. For the high form, rs1 is the input high word and rs2 is the input low word.
fixed
source
source
fixed
destination
OP
31..25
0101110
24..20
rs2=x12
19..15
rs1=x11
14..12
000
11..7
rd=x10
6..0
0110011
Execution Data Path
X(rs1)[31:0]
0x89ABCDEF
X(rs2)[31:0]
0x01234567
rs1 >> 1
0x44D5E6F7
rs1 >> 7
0x0113579B
rs1 >> 8
0x0089ABCD
rs2 << 31
0x80000000
rs2 << 24
0x67000000
result
0xA24F1AA1
Architectural Result
a0(x10) = 0xA24F1AA1
This animation shows only official ISA fields and architectural state; it does not model a complete hash algorithm or microarchitecture.
Quick Understanding & Search Notes
SHA512SIG0H is a Zknh scalar cryptography instruction for SHA-512 RV32 split transform. This page is checked against the official scalar crypto extension, avoiding confusion among round functions, key schedule steps, and operand sources.
sha512sig0h computes one half of a SHA-512 64-bit sigma result on RV32 and must be paired with the matching h/l instruction.
Scalar crypto instructions use integer X registers, and the official spec requires the relevant crypto instructions to be implemented with data-independent execution latency.
RV32 SHA-512 split forms need the official h/l or reversed-source sequence to assemble the full 64-bit result.
Common Usage Scenarios
Crypto & Security
Understand this scenario with real code like «sha512sig0h a0, a1, a2».
Hash Algorithms
Understand this scenario with real code like «sha512sig0h a0, a1, a2».
Pre-Use Checklist
Syntax Check
- Verify rd, rs1, rs2 (and rs3) are valid GPRs.
- Confirm funct3 and funct7 encoding is correct.
Semantic Check
- Check if the result affects subsequent branches or address calculations.
- Ensure the rd register is not overwritten by another instruction.
Pitfalls / Common Confusions
RV32 only. rs1=upper 32 bits, rs2=lower 32 bits (ordering may be confusing).
Must be paired with sha512sig0l for the complete 64-bit σ0 result.
h=high, l=low suffix mapping; do not swap.
FAQ
Is SHA512SIG0H a complete algorithm implementation?
No. It computes one RV32 word of the SHA-512 Sigma0 result; the documented L/H paired sequence combines the complete transform.