vrlwmi

Vector Rotate Left Word then Mask Insert VX-form

vrlwmi VRT,VRA,VRB

Rotates the contents of each word element in a vector left by a specified number of bits and inserts the result into another vector under control of a mask.

Encoding

Binary Layout

0:5

VRT

6:10

VRA

11:15

VRB

16:31

Format VX-form

Opcode 0x10000085

Extension VMX (AltiVec)

Operands

VRT
Target Vector Register
VRA
Source Vector Register
VRB
Source Vector Register

Example

vrlwmi v1, v2, v3

Reference

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

Description

Rotates each word element of VRA left by the number of bits specified in VRB, then inserts the rotated result into VRT under control of a mask generated from VRB. No condition flags are affected.

Operation

for i in 0 to 3 do
  shamt ← (VRB[i*32+27:i*32+31]) & 0x1F
  word ← (u32)VRA[i*32:(i*32+31)]
  rotated ← (word << shamt) | (word >> (32 - shamt))
  mask ← Generate_Mask_From_VRB(i)
  VRT[i*32:(i*32+31)] ← (VRT[i*32:(i*32+31)] & ~mask) | (rotated & mask)
end for

Programming Note

The vrlwmi instruction is useful for performing masked insertions after rotating word elements. Ensure that the mask bits (11:15 and 19:23) are set correctly to achieve the desired insertion pattern. This instruction operates on vector registers, so ensure that the Vector Facility is enabled in the Machine State Register (MSR).