CPOP

Population Count

CPOP rd, rs1

Counts the number of set bits (1s) in the register.

Encoding

Binary Layout

011000000010

31:20

rs1

19:15

001

14:12

rd

11:7

0010011

6:0

 

Format I-Type

Opcode 0x60201013

Extension Zbb

Operands

• rd
  Destination register (integer)
• rs1
  Source

Example

CPOP x10, x11

// Hamming weight calculation.

Related

Across architectures

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

More in Zbb

Reference

View in RISC-V Unprivileged ISA Specification ↗ RISC-V ISA Manual

Description

CPOP counts the number of set bits (population count / Hamming weight) in rs1 and writes the count to rd.

Operation

R[rd] = count_set_bits(R[rs1]);