cbnz

Compare and Branch Not Zero (64-bit)

CBNZ <Xt>, <label>

Branches if 64-bit register is not zero.

Pseudocode Operation

if Xt != 0 then
  PC ← PC + SignExtend(imm19 << 2, 64)

Example

CBNZ x3, label

Encoding

Binary Layout

1

31

011010

30:25

1

24

imm19

23:5

Rt

4:0

 

Format Branch

Opcode 0xB5000000

Extension Base

Operands

• Xt
  Reg
• label
  Label

Related

Other forms of cbnz

• cbnz Compare and Branch Not Zero
• cbnz Compare and Branch Non-Zero (Thumb)

Across architectures

Compare and Branch : how x86, ARM, RISC-V, and PowerISA each do this.

More in Base

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x35000000	CBNZ <Wt>, <label>		A64		0 | 011010 | 1 | imm19 | Rt
0xB5000000	CBNZ <Xt>, <label>		A64		1 | 011010 | 1 | imm19 | Rt

Description

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

Operation

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