PC-relative Branch Range
Conditional branches use the B-type immediate, a signed PC-relative offset in 2-byte units, giving an approximate reach of +/-4 KiB from the current PC.
RISC-V Unprivileged ISA, RV32I control transfer instructionsBNE
RISC-V BNE Instruction Details
Instruction ManualB-typeBranch to PC-relative offset if rs1 is not equal to rs2
Instruction Syntax
bne rs1, rs2, offset
Operand Breakdown
Source rs1: first comparison operand.
Source rs2: second comparison operand.
Immediate offset: 13-bit signed branch offset (bit 0 is implicitly 0, ±4 KiB range).
RV32IControl TransferBranch
Related Search Terms
Instruction Encoding
31..25
imm[12|10:5]
24..20
rs2
19..15
rs1
14..12
funct3
11..7
imm[4:1|11]
6..0
opcode
BNE uses opcode 1100011 (0x63), funct3 001. The rs1 and rs2 fields hold the comparison operands, and the 13-bit immediate encodes the branch offset (±4 KiB).
Format: B-type
opcode: 1100011 (0x63)
funct3: 001 (0x1)
Instruction Behavior
BNE (B-type, opcode=1100011, funct3=001) compares rs1 and rs2 and takes the branch if they are not equal. The B-immediate encodes a signed 12-bit offset in multiples of 2, giving a ±4 KiB range. When the condition is false, fallthrough execution occurs.
Quick Understanding & Search Notes
BNE is a conditional branch: when rs1 and rs2 satisfy the not equal condition, the PC branches to the current PC plus the B-type offset; otherwise execution falls through.
The B-type branch offset is encoded in 2-byte units and reaches about +/-4 KiB from the current PC.
RISC-V conditional branches do not write rd and do not save a return address.
Official Spec Notes
These notes are checked against the RISC-V Unprivileged ISA manual and summarize operation semantics, immediate ranges, and edge behavior.
No Link Register Write
Conditional branches only update the PC based on the comparison result. They do not write rd or save a return address; use JAL/JALR forms for calls and returns.
RISC-V Unprivileged ISA, RV32I control transfer instructionsCommon Usage Scenarios
Comparison & Detection
Understand this scenario with real code like «bne x3, x4, label # if x3 != x4, branch to label».
Pre-Use Checklist
Syntax Check
- Confirm the current instruction format is B-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
Range ±4 KiB
Complementary to BEQ; ensure correct condition logic
FAQ
What is the BNE branch range?
Conditional branches use a B-type immediate, giving an approximate reach of +/-4 KiB from the current PC.
What is the difference between signed and unsigned branches?
BLT/BGE compare as signed integers; BLTU/BGEU compare as unsigned integers. BEQ/BNE only test equality of the bit patterns.