cbz

Compare and Branch Zero

CBZ <Wt>, <label>

Branches if register is zero.

Details

Compare and Branch if Zero. Compares the contents of the 32-bit register Wt with zero, and branches to the target address if the result equals zero. This is a non-conditional branch that does not affect the condition flags. AArch64-only instruction.

Pseudocode Operation

if Wt == 0 then PC ← PC + (imm19 << 2)

Example

CBZ w3, label

Encoding

Binary Layout
0
011010
0
imm19
Rt
 
Format Branch
Opcode 0x34000000
Extension Base

Operands

  • Wt
    Reg
  • label
    Label

Reference (Arm A64 ISA)

Instruction Forms

Encoding Instruction ISA Bit pattern
0x34000000 CBZ <Wt>, <label> A64 0 | 011010 | 0 | imm19 | Rt
0xB4000000 CBZ <Xt>, <label> A64 1 | 011010 | 0 | imm19 | Rt

Description

Compare and Branch on Zero compares the value in a register with zero, and conditionally branches to a label at a PC-relative offset if the comparison is equal. It provides a hint that this is not a subroutine call or return. This instruction does not affect condition flags.

Operation

bits(datasize) operand1 = X[t, datasize];
if IsZero(operand1) == TRUE then
    BranchTo(PC64 + offset, BranchType_DIR, TRUE);
else
    BranchNotTaken(BranchType_DIR, TRUE);