Does bexti access memory?
No. It reads integer register operands and writes rd only.
BEXTI
RISC-V BEXTI Instruction Details
Instruction ManualI-typeExtract single bit by immediate index
Instruction Syntax
bexti rd, rs1, uimm
Operand Breakdown
Destination rd: receives the result of the single-bit extract, invert, or set operation; a write to rd=x0 is discarded.
Source rs1: supplies the XLEN-bit value whose bit is extracted, inverted, or set.
shamt: immediate-encoded bit index. RV32 uses shamt[4:0] and encodings with shamt[5]=1 are reserved; RV64 uses shamt[5:0].
ZbsBit ManipulationSingle-Bit Operation
Related Search Terms
Instruction Behavior
bexti is a Zbs single-bit extract instruction. The bit index comes from the immediate field.
BEXTI Decode And Execute Animation
Starts with machine-code field decoding, then shows operand reads, instruction-specific execution, and ISA-visible state update.
rd
rs1
shamt
bexti
,
,
Execution Context
a0(x10)
0x00001000
31..25
24..20
19..15
14..12
11..7
6..0
0100100
fixed imm[11:5]
01100
shamt[4:0]
01010
rs1
101
funct3
00101
rd
0010011
opcode
Execution Data Path
instruction
0x48C55293
opcode
0010011 -> OP-IMM
funct3
101 -> BEXTI
imm[11:5]
imm[11:5]=0100100 fixed
rd / rs1
t0(x5) / a0(x10)=0x00001000
imm[11:5] + shamt[4:0]
imm[11:5]=0100100 fixed -> index=12
single-bit extract
(0x00001000 >> 12) & 1 = 1
x5
t0(x5) = 0x00000001
Current Step
Concept Step: receive the 32-bit instruction encoding
The machine code is split by the current instruction format; the animation starts from encoding/decode.
encoding: 0x48C55293
syntax : bexti t0(x5), a0(x10), 12
result : t0(x5) = 0x00000001
Architectural Result
t0(x5) = 0x00000001
This animation shows ISA-visible decode and state changes, not any specific CPU pipeline, cache, prediction, or timing implementation.
Quick Understanding & Search Notes
bexti is a Zbs single-bit extract instruction. The bit index comes from the immediate field.
These instructions are part of a B-extension subset and operate on XLEN-wide integer register values.
The immediate field width depends on XLEN; RV32 encodings with shamt[5]=1 are reserved, while RV64 encodes 0..63.
bext/bexti returns 0 or 1; it does not preserve the original bit position.
Common Usage Scenarios
Bit Operations & Masks
Understand this scenario with real code like «bexti x10, x11, 2 ; x10 = (x11 >> 2) & 1».
Comparison & Detection
Understand this scenario with real code like «bexti x10, x11, 2 ; x10 = (x11 >> 2) & 1».
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
The immediate field width depends on XLEN; RV32 encodings with shamt[5]=1 are reserved, while RV64 encodes 0..63.
bext/bexti returns 0 or 1; it does not preserve the original bit position.
FAQ
How is the bit index selected for bexti?
The immediate encodes the bit position directly, with the legal range determined by XLEN.