xxsel

VSX Vector Select

xxsel XT, XA, XB, XC

Selects elements from two source vectors based on a mask vector.

Encoding

Binary Layout

60

XT

XA

XB

XC

3

 

Format XX4-form

Opcode 0xF0000030

Extension VSX

Operands

• XT
  Target
• XA
  True Src
• XB
  False Src
• XC
  Mask
• VRT
  Target Vector Register
• VRA
  Source Vector Register
• VRB
  Source Vector Register
• VRC
  Source Vector Register

Example

xxsel vs1, vs2, vs3, vs4

Registers Altered

MSR

Related

More in VSX

Reference

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

Description

Selects bits from XA or XB for each bit position based on the corresponding bit in the mask register XC. Where XC has a 1 bit, the result takes the bit from XA; where XC has a 0 bit, the result takes the bit from XB. This is a VSX instruction with no effect on condition or status flags.

Operation

for i in 0 to 127 do
  if XC[i] = 1 then
    XT[i] ← XA[i]
  else
    XT[i] ← XB[i]

Programming Note

The xxsel instruction is commonly used for conditional vector selection based on a mask. Ensure that the VSX feature is enabled in the MSR register to avoid an exception. The source and destination vectors must be properly aligned, typically requiring 16-byte alignment for optimal performance.