======================================================================== SIMD popcount

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

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

Paper

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

__ https://arxiv.org/abs/1611.07612

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.

__ https://github.com/gcc-mirror/gcc/commit/e0aa57d6b04908affdf4655a6b4a9f2d4d03483b

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.

__ results/README.rst

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__

__ http://danluu.com/assembly-intrinsics/

See also

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

__ https://github.com/kimwalisch/libpopcnt

.. vim: nowrap