xxpermdi

VSX Permute Doubleword Immediate

xxpermdi XT, XA, XB, DM

Selects two doublewords from the four available in source registers XA and XB based on a 2-bit selector.

Encoding

Binary Layout

0:4

5:9

10:14

16:20

22:26

27:30

Format XX3-form

Opcode 0xF0000050

Extension VSX

Operands

XT
Target
XA
Source A
XB
Source B
DM
Selector (2 bits)

Example

xxpermdi 0, 1, 1, 2

// Swap high/low doublewords of vs1.

Registers Altered

MSR

Reference

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

Description

Selects two 64-bit doublewords from source registers XA and XB and places them in target register XT. The 2-bit selector DM controls which doubleword is chosen: bits [1:0] of DM select from XA for the high half of XT, and bits [3:2] select from XB for the low half. No condition registers or status flags are affected.

Operation

case DM[1:0]:
  0: XT[0:63] ← XA[0:63]
  1: XT[0:63] ← XA[64:127]
  otherwise: XT[0:63] ← ?
case DM[3:2]:
  0: XT[64:127] ← XB[0:63]
  1: XT[64:127] ← XB[64:127]
  otherwise: XT[64:127] ← ?

Extended Mnemonics

Extended Mnemonic	Equivalent Instruction
xxspltd
xxmrghd
xxmrgld
xxswapd

Programming Note

The xxpermdi instruction is used to permute doublewords from two VSX registers into a third register based on an immediate value. Ensure that the VSX facility is enabled in the MSR register; otherwise, a VSX_Unavailable exception will be raised. The immediate value DM controls which doubleword elements are selected from VSR[XB] for placement in VSR[XT].