[ruby-cvs:64300] nobu:r57134 (trunk): st.c: fix st_hash* functions [Bug #13019]
nobu at ruby-lang.org
nobu at ruby-lang.org
Wed Dec 21 15:22:17 JST 2016
nobu 2016-12-21 15:22:16 +0900 (Wed, 21 Dec 2016)
New Revision: 57134
https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=57134
Log:
st.c: fix st_hash* functions [Bug #13019]
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
Author: Sokolov Yura aka funny_falcon <funny.falcon at gmail.com>
Modified files:
trunk/include/ruby/st.h
trunk/st.c
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