vmaxub

Vector Maximum Unsigned Byte

vmaxub vD, vA, vB

Selects maximum value per byte (unsigned).

Encoding

Binary Layout

4

0:5

vD

6:10

vA

11:15

vB

16:20

4

21:31

 

Format VA-form

Opcode 0x10000002

Extension VMX (AltiVec)

Operands

• vD
  Target
• vA
  Src A
• vB
  Src B

Example

vmaxub vd, va, vb

Registers Altered

MSR

Related

More in VMX (AltiVec)

Reference

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

Description

Selects the maximum unsigned value for each corresponding byte pair from vA and vB, storing the results in vD. This is a vector operation that performs 16 independent byte-wise maximum comparisons in parallel. No condition flags or status fields are affected.

Operation

for i in 0 to 15 do
  vD[8*i:8*i+7] ← MAX_UNSIGNED(vA[8*i:8*i+7], vB[8*i:8*i+7])
end for

Programming Note

The vmaxub instruction is used to perform element-wise comparison of unsigned bytes from two vector registers and store the maximum values in a third register. Ensure that the Vector Facility (MSR.VEC) is enabled before using this instruction; otherwise, it will raise an exception. This instruction operates on 16-byte vectors, so ensure proper alignment for optimal performance.