ClickHouse/base/memcpy
2020-03-03 05:43:59 +03:00
..
impl Remove excessive empty lines 2020-03-03 05:43:59 +03:00
CMakeLists.txt libs/ → base/ 2020-02-14 17:48:30 +03:00
memcpy.c libs/ → base/ 2020-02-14 17:48:30 +03:00
memcpy.h libs/ → base/ 2020-02-14 17:48:30 +03:00
README.md libs/ → base/ 2020-02-14 17:48:30 +03:00

Internal implementation of memcpy function.

It has the following advantages over libc-supplied implementation:

  • it is linked statically, so the function is called directly, not through a PLT (procedure lookup table of shared library);
  • it is linked statically, so the function can have position-dependent code;
  • your binaries will not depend on glibc's memcpy, that forces dependency on specific symbol version like memcpy@@GLIBC_2.14 and consequently on specific version of glibc library;
  • you can include memcpy.h directly and the function has the chance to be inlined, which is beneficial for small but unknown at compile time sizes of memory regions;
  • this version of memcpy pretend to be faster (in our benchmarks, the difference is within few percents).

Currently it uses the implementation from Linwei (skywind3000@163.com). Look at https://www.zhihu.com/question/35172305 for discussion.

Drawbacks:

  • only use SSE 2, doesn't use wider (AVX, AVX 512) vector registers when available;
  • no CPU dispatching; doesn't take into account actual cache size.

Also worth to look at: