cmpi

Compare Immediate

cmpi BF, L, RA, SI

Compares the contents of register RA with a sign-extended immediate value.

Encoding

Binary Layout

Format D-form

Opcode 0x2C000000

Extension Base

Operands

BF
Condition Register Field
L
Size (0=32-bit, 1=64-bit)
RA
Source Register
SI
Signed 16-bit Immediate

Example

cmpi cr0, 1, r3, -5

// Compare r3 vs -5 (64-bit signed).

Registers Altered

CR, XER

Across architectures

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

Reference

View in PowerISA v3.1C Specification ↗ OPF Power ISA v3.1C

Description

The contents of register RA ((RA)32:63 sign-extended to 64 bits if L=0) are compared with the sign-extended value of the SI field, treating the operands as signed integers. The result of the comparison is placed into CR field BF.

Operation

if L = 0 then a ←EXTS((RA)32:63)
else a ←(RA)
if      a < EXTS(SI) then c ←0b100
else if a > EXTS(SI) then c ←0b010
else                      c ←0b001
CR4×BF+32:4×BF+35 ←c || XERSO

Extended Mnemonics

Extended Mnemonic	Equivalent Instruction
cmpdi
cmpwi

Programming Note

The cmpi instruction is commonly used for signed integer comparisons where one operand is an immediate value. Be cautious with the alignment of the register RA, as incorrect alignment can lead to unexpected results. This instruction operates at user privilege level and does not generate exceptions under normal circumstances.