vstribl

Vector String Isolate Byte Left

vstribl vD, vB

Stores the leftmost byte of each element in a vector register to memory.

Encoding

Binary Layout

0:5

VRT

6:10

11:15

VRB

16:20

22:31

Format VX-form

Opcode 0x1000000D

Extension VMX (AltiVec)

Operands

vD
Target
vB
Source
VS32
Target Vector Register
VS31
Source Vector Register
RB
Base Address General Purpose Register

Example

vstribl vd, vb

Reference

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

Description

Isolates the leftmost non-zero byte in each element of the source vector register and stores the result in the destination vector register. This is a VMX instruction that does not affect condition registers or status fields.

Operation

for i in 0 to 15 do
  found ← 0
  for j in 0 to 7 do
    if vB[i*8 + j] != 0 then
      vD[i*8:(i+1)*8-1] ← vB[j*8:(j+1)*8-1]
      found ← 1
      break
    end if
  end for
  if found = 0 then
    vD[i*8:(i+1)*8-1] ← 0
  end if
end for

Programming Note

The vstribl instruction is useful for extracting the first character from strings stored in vector registers. Ensure that the input vectors are properly aligned to avoid alignment faults. This instruction operates at user privilege level and will raise an exception if executed in a kernel context without proper permissions.