Does SHA256SUM0 use floating-point or vector registers?
No. These scalar crypto extension instructions use integer X registers.
SHA256SUM0
RISC-V SHA256SUM0 Instruction Details
Instruction ManualI-typeSHA-256 Σ0 function (uppercase): ROTR(rs1,2) ^ ROTR(rs1,13) ^ ROTR(rs1,22)
Instruction Syntax
sha256sum0 rd, rs1
Operand Breakdown
Destination rd: general-purpose register receiving the result.
Source rs1: register holding the first operand.
Immediate imm: 12-bit signed value, sign-extended before operation with rs1.
ZknhCrypto & Security
Instruction Behavior
sha256sum0 implements the SHA-256 compression Σ0 function: Σ0(x) = ROTR(x, 2) ^ ROTR(x, 13) ^ ROTR(x, 22). It is defined for RV32/RV64: RV32 operates on all of X(rs1), while RV64 uses X(rs1)[31:0] and sign-extends the 32-bit result before writing rd.
SHA256SUM0 Decode And Execute Animation
Bounded teaching inputs execute the official SHA-256 fixed-width bit operations; this does not model a complete algorithm or microarchitecture.
rd
rs1
sha256sum0
,
SHA256SUM0 is defined in RV32/RV64; RV64 uses X(rs1)[31:0] and sign-extends the 32-bit result to XLEN.
fixed selector
source
fixed
destination
OP-IMM
31..20
000100000000
19..15
rs1=x11
14..12
001
11..7
rd=x10
6..0
0010011
Execution Data Path
inb
0x89ABCDEF
ror32(inb, 2)
0xE26AF37B
ror32(inb, 13)
0x6F7C4D5E
ror32(inb, 22)
0xAF37BE26
result
0x22210003
Architectural Result
a0(x10) = 0x22210003
This animation shows only official ISA fields and architectural state; it does not model a complete hash algorithm, pipeline, cache, or timing implementation.
Quick Understanding & Search Notes
SHA256SUM0 is a Zknh scalar cryptography instruction for SHA-256 transform. This page is checked against the official scalar crypto extension, avoiding confusion among round functions, key schedule steps, and operand sources.
sha256sum0 performs the SHA-256 uppercase Sigma compression transform using the official fixed rotate-right combination.
Scalar crypto instructions use integer X registers, and the official spec requires the relevant crypto instructions to be implemented with data-independent execution latency.
Common Usage Scenarios
Crypto & Security
Understand this scenario with real code like «sha256sum0 a0, a1».
Hash Algorithms
Understand this scenario with real code like «sha256sum0 a0, a1».
Pre-Use Checklist
Syntax Check
- Verify the immediate field is within the valid range.
- Confirm source register rs1 points to the correct operand.
Semantic Check
- Check if the immediate sign-extension matches expectations.
- Ensure the result register rd has a clear purpose.
Pitfalls / Common Confusions
Σ0 (sum0, uppercase) for compression; σ0 (sig0, lowercase) for message schedule. Different rotate/shift amounts.
FAQ
Is SHA256SUM0 a complete algorithm implementation?
No. It implements one SHA-2 Sigma transform; software still schedules the remaining SHA-2 computation.