cbnz

Compare and Branch Non-Zero (Thumb)

CBNZ <Rn>, <label>

Branches to label if register is not zero (Thumb-only).

Details

Compares the value in Rn with zero and branches to the label if not equal. The branch offset is encoded as an unsigned 6-bit immediate (i and imm5 combined, shifted left by 1 to form a 7-bit address offset). This instruction is T32 (Thumb)-only and does not affect condition flags. If the branch is not taken, execution continues sequentially.

Pseudocode Operation

if Rn != 0 then PC ← PC + (i:imm5:0 << 1) else PC ← PC + 2

Example

CBNZ r1, label

Encoding

Binary Layout
1011
1
0
i
1
imm5
Rn
 
Format Thumb Branch
Opcode 0xB900
Extension T32 (Thumb)

Operands

  • Rn
    Register
  • label
    Label

Reference (Arm AArch32 ISA)

Instruction Forms

Encoding Instruction ISA Bit pattern
0xB900 CBNZ{<q>} <Rn>, <label> T32 1011 | 1 | 0 | i | 1 | imm5 | Rn

Description

Compare and Branch on Nonzero and Compare and Branch on Zero compare the value in a register with zero, and conditionally branch forward a constant value. They do not affect the condition flags.

Operation

EncodingSpecificOperations();
if nonzero != IsZero(R[n]) then
    CBWritePC(PC + imm32);