vsr

Vector Shift Right

vsr vD, vA, vB

Shifts vector right by octet count in vB.

Encoding

Binary Layout

0:5

6:10

11:15

16:20

708

21:31

Format VX-form

Opcode 0x100002C4

Extension VMX (AltiVec)

Operands

vD
Target
vA
Data
vB
Shift Count

Example

vsr vd, va, vb

Reference

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

Description

Shifts the 128-bit value in vA right by the number of octets (bytes) specified in the low 5 bits of vB, filling vacated positions on the left with zeros. The shift amount is taken from bits 123-127 of vB (the low-order 5 bits). No condition register fields are affected.

Operation

shift_count ← vB[123:127]
if shift_count > 16 then shift_count ← 16
vD ← vA >> (shift_count * 8)

Programming Note

The vsr instruction is commonly used for bit manipulation in vector operations, where each element of the vector is shifted right by a number of bits specified in a control register. Ensure that the control register contains valid shift amounts to avoid unexpected results. This operation does not require any specific privilege level and will not generate exceptions unless there are alignment issues with the vector data.

vsr