vctzlsbb

Vector Count Trailing Zero Least Significant Bits Byte

vctzlsbb RA, vB

Counts the number of trailing zero bits in each byte element of a vector.

Encoding

Binary Layout

4

0:5

RA

6:10

0

11:15

vB

16:20

1543

21:31

 

Format VX-form

Opcode 0x10010602

Extension VMX (AltiVec)

Operands

• RA
  Target GPR
• vB
  Source
• VRT
  Target Vector Register
• VRA
  Source Vector Register

Example

vctzlsbb r4, vb

Related

More in VMX (AltiVec)

Reference

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

Description

Counts the number of trailing zero bits in each byte of the source vector and stores the scalar result (the count from the least-significant byte) in a GPR. This VMX instruction updates CR6 based on the result to indicate whether all bytes contain zero or not.

Operation

RA ← count_trailing_zeros_lsb_byte(vB[0:7])

Programming Note

Use vctzlsbb to efficiently count the number of contiguous trailing zero bytes with a zero least-significant bit. Ensure that the input vector is properly aligned and that you have the necessary privileges to execute this instruction. The result is stored in a general-purpose register, so be mindful of register usage and dependencies.