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README.rst

SIMD popcount

Sample programs for my article http://0x80.pl/articles/sse-popcount.html

https://travis-ci.org/WojciechMula/sse-popcount.svg?branch=master

Paper

Daniel Lemire, Nathan Kurz and I published an article Faster Population Counts using AVX2 Instructions.

Introduction

Subdirectory original contains code from 2008 --- it is 32-bit and GCC-centric. The root directory contains fresh C++11 code, written with intrinsics and tested on 64-bit machines.

There are two programs:

  • verify --- it tests if all non-lookup implementations counts bits properly;
  • speed --- benchmarks different implementations of popcount procedure; please read help to find all options (run the program without arguments).

There are several targets:

  • default --- builtin functions, SSE and popcnt instructions;
  • AVX2 --- all above plus AVX2 implementations;
  • AVX512BW --- all above plus experimental AVX512BW code;
  • AVX512VBMI --- all above plus experimental AVX512VBMI code;
  • AVX512 VPOPCNT --- all above plus experimental AVX512 VPOPCNT code (should be compilable with very recent GCC, software emulator doesn't support this extension yet);
  • arm --- builtin and ARM Neon implementations.

Type make help to find out details. To run the default target benchmark simply type make.

Available implementations

procedure description
lookup-8 lookup in std::uint8_t[256] LUT
lookup-64 lookup in std::uint64_t[256] LUT
bit-parallel naive bit parallel method
bit-parallel-optimized a bit better bit parallel
bit-parallel-optimized2 better utilization of 2- and 4-bit subwords
bit-parallel-mul bit-parallel with fewer instructions
bit-parallel32 naive bit parallel method (32 bit)
bit-parallel-optimized32 a bit better bit parallel (32 bit)
harley-seal Harley-Seal popcount (4th iteration)
sse-bit-parallel SSE implementation of bit-parallel-optimized (unrolled)
sse-bit-parallel-original SSE implementation of bit-parallel-optimized
sse-bit-parallel-better SSE implementation of bit-parallel with fewer instructions
sse-harley-seal SSE implementation of Harley-Seal
sse-lookup SSSE3 variant using pshufb instruction (unrolled)
sse-lookup-original SSSE3 variant using pshufb instruction
avx2-lookup AVX2 variant using pshufb instruction (unrolled)
avx2-lookup-original AVX2 variant using pshufb instruction
avx2-harley-seal AVX2 implementation of Harley-Seal
cpu CPU instruction popcnt (64-bit variant)
sse-cpu load data with SSE, then count bits using popcnt
avx2-cpu load data with AVX2, then count bits using popcnt
avx512-harley-seal AVX512 implementation of Harley-Seal
avx512bw-shuf AVX512BW implementation uses shuffle instruction
avx512vbmi-shuf AVX512VBMI implementation uses shuffle instruction
avx512-vpopcnt AVX512 VPOPCNT
builtin-popcnt builtin for popcnt
builtin-popcnt32 builtin for popcnt (32-bit variant)
builtin-popcnt-unrolled unrolled builtin-popcnt
builtin-popcnt-unrolled32 unrolled builtin-popcnt32
builtin-popcnt-unrolled-errata unrolled builtin-popcnt avoiding false-dependency
builtin-popcnt-unrolled-errata-manual unrolled builtin-popcnt avoiding false-dependency (asembly code)
builtin-popcnt-movdq builtin-popcnt where data is loaded via SSE registers
builtin-popcnt-movdq-unrolled builtin-popcnt-movdq unrolled
builtin-popcnt-movdq-unrolled_manual builtin-popcnt-movdq unrolled (assembly code)
neon-vcnt ARM Neon using VCNT
neon-HS Harley-Seal using Neon VCNT
aarch64-cnt ARMv8 Neon using CNT

Performance results

The subdirectory results contains performance results from various computers. If you can, please contribute.

Acknowledgments

  • Kim Walisch (@kimwalisch) wrote Harley-Seal scalar implementation.
  • Simon Lindholm (@simonlindholm) added unrolled versions of procedures.
  • Dan Luu (@danluu) agreed to include his procedures (builint-*) into this project. More details in Dan's article Hand coded assembly beats intrinsics in speed and simplicity

See also

  • libpopcnt --- library by Kim Walisch utilizing methods from our paper.
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