Does SEXT.B access memory?
No. It only reads and writes integer registers; any memory access must be performed by a separate load or store instruction.
SEXT.B
RISC-V SEXT.B Instruction Details
Instruction ManualR-typeSign-extend byte
Instruction Syntax
sext.b rd, rs1
Operand Breakdown
Destination rd: register receiving the operation result.
Source rs1: register holding the first operand.
Source rs2: register holding the second operand.
BZbbBit ManipulationInteger Operation
Instruction Behavior
Sign-extends the least-significant 8 bits of rs to XLEN. Replaces slli+srai (sign-ext) or slli+srli (zero-ext) sequences. Part of Zbb.
Quick Understanding & Search Notes
SEXT.B is a B/Zbb instruction for sign-extend low byte. This page is checked against the official B extension semantics, with emphasis on XLEN, W suffixes, .uw suffixes, and bitwise or rotate boundaries.
Only the low 8 bits are read and bit 7 is sign-extended.
It is not zero-extension; use masking or an appropriate zero-extension form for unsigned bytes.
Common Usage Scenarios
Bit Operations & Masks
Understand this scenario with real code like «sext.b x10, x11 ; x10 = sign_ext(x11[7:0])».
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
Only extends lower 8 bits
FAQ
What is the result width of SEXT.B?
Except that W-suffixed forms produce a 32-bit result then sign-extend and .uw forms first extract a 32-bit unsigned operand, the result is written to rd at XLEN width.