vclrlb

Vector Clear Left Bytes

vclrlb vD, vA, RB

Clears the leftmost bytes in a vector register based on the value in a general-purpose register.

Encoding

Binary Layout

4

0:5

vD

6:10

vA

11:15

RB

16:20

397

21:31

 

Format VX-form

Opcode 0x1000018D

Extension VMX (AltiVec)

Operands

• vD
  Target
• vA
  Source
• RB
  Count (GPR)
• VRT
  Target Vector Register
• VRA
  Source Vector Register

Example

vclrlb vd, va, r5

Registers Altered

MSR

Related

More in VMX (AltiVec)

Reference

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

Description

The contents of VSR[VRA+32] are placed into VSR[VRT+32] with the leftmost 16-N bytes set to 0, where N is the integer value in GPR[RB] or 16 if GPR[RB] > 15.

Operation

if MSR.VEC=0 then
    Vector_Unavailable()
N ← (GPR[RB] > 15) ? 16 : GPR[RB]
do i = 0 to N-1
    VSR[VRT+32].byte[15-i] ← VSR[VRA+32].byte[15-i]
end
do i = N to 15
    VSR[VRT+32].byte[15-i] ← 0x00
end

Programming Note

The vclrlb instruction is useful for clearing the leftmost bytes of a vector register based on the value in GPR[RB]. Ensure that the Vector Facility (MSR.VEC) is enabled; otherwise, a Vector_Unavailable exception will be raised. Be cautious with alignment and ensure that the values in VRA and VRT are correctly set to avoid unintended data manipulation.