[ruby-core:78587] [Ruby trunk Bug#13019] Fix st_hash* functions

Issue #13019 has been updated by Yura Sokolov.


It passes SMHasher (at least, little-endian variant).

----------------------------------------
Bug #13019: Fix st_hash* functions
https://bugs.ruby-lang.org/issues/13019#change-61972

* Author: Yura Sokolov
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: 
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
----------------------------------------
Previous implementation had an issues:
- macros murmur1 assumes murmur_step takes rotation value
  as a second argument
- but murmur_step second argument is "next block"
- this makes st_hash_uint and st_hash_end to not mix high bits of
  hash value into lower bits
- this leads to pure hash behavior on doubles and mixing hashes using st_hash_uint.
  It didn't matter when bins amount were prime numbers, but it hurts
  when bins are powers of two.

Mistake were created cause of attempt to co-exist Murmur1 and Murmur2
in a same code.

Change it to single hash-function implementation.
- block function is in a spirit of Murmur functions,
  but handles inter-block dependency a bit better (imho).
- final block is read in bit more optimal way on CPU with unaligned word access,
- final block is mixed in simple way,
- finalizer is taken from MurmurHash3 (it makes most of magic :) )
  (64bit finalizer is taken from
  http://zimbry.blogspot.ru/2011/09/better-bit-mixing-improving-on.html)

Also remove ST_USE_FNV1: it lacks implementation of many functions,
and looks to be abandoned

---Files--------------------------------
0001-st.c-fix-st_hash-functions.patch (10.9 KB)


-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:[e-mail]?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>