cbz

Compare and Branch Zero (Thumb)

CBZ <Rn>, <label>

Branches to label if register is zero (Thumb-only, does not affect flags).

Pseudocode Operation

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

Example

CBZ r1, label

Encoding

Binary Layout

1011

15:12

0

11

0

10

i

9

1

8

imm5

7:3

Rn

2:0

 

Format Thumb Branch

Opcode 0xB100

Extension T32 (Thumb)

Operands

• Rn
  Register
• label
  Label

Related

Other forms of cbz

• cbz Compare and Branch Zero
• cbz Compare and Branch Zero (64-bit)

Across architectures

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

More in T32 (Thumb)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0xB100	CBZ{<q>} <Rn>, <label>		T32		1011 | 0 | 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);