popcntb

Population Count Bytes

popcntb RA,RS

Counts the number of one bits in each byte of a register.

Encoding

Binary Layout

31

0:5

RS

6:10

RA

11:15

///

16:20

122

21:30

/

31

 

Format X-form

Opcode 0x7C0000F4

Extension Base

Operands

• RA
  Target General Purpose Register
• RS
  Source General Purpose Register

Example

popcntb r4, r3

Related

Across architectures

Population Count : how x86, ARM, RISC-V, and PowerISA each do this.

More in Base

Reference

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

Description

A count of the number of one bits in each byte of register RS is placed into the corresponding byte of register RA. This number ranges from 0 to 8, inclusive.

Operation

for i = 0 to 7
    n ← 0
    for j = 0 to 7
        if (RS)(i×8)+j = 1 then
            n ← n+1
    RA(i×8):(i×8)+7 ← n