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implement Jenkins’ one-at-a-time hash, which has better avalanche

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behaviour than DJB’s CDB hash (good if using more than one byte)
and probably no funnels

the CDB hash is good for short (5-6 char) ASCII keys though
This commit is contained in:
tg 2009-08-27 16:29:21 +00:00
parent fb6d8cd895
commit 4c1a99da7c
1 changed files with 26 additions and 1 deletions
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27
dot.mkshrc
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@ -1,4 +1,4 @@
# $MirOS: src/bin/mksh/dot.mkshrc,v 1.46 2009/08/27 16:03:52 tg Exp $
# $MirOS: src/bin/mksh/dot.mkshrc,v 1.47 2009/08/27 16:29:21 tg Exp $
#-
# Copyright (c) 2002, 2003, 2004, 2006, 2007, 2008, 2009
# Thorsten Glaser <tg@mirbsd.org>
@ -294,6 +294,31 @@ function Lcdbhash {
Lcdbhash_add "$@"
}
# Jenkins one-at-a-time hash (not via stdio, for speed)
typeset -Z11 -Uui16 Loaathash_result
function Loaathash_add {
typeset u=$-
set +U
typeset s="$*"
typeset -i i=0 n=${#s}
while (( i < n )); do
((# Loaathash_result += 1#${s:(i++):1} ))
((# Loaathash_result += Loaathash_result << 10 ))
((# Loaathash_result ^= Loaathash_result >> 6 ))
done
[[ $u = *U* ]] && set -U
:
}
function Loaathash {
Loaathash_result=0 # hmm...
Loaathash_add "$@"
((# Loaathash_result += Loaathash_result << 3 ))
((# Loaathash_result ^= Loaathash_result >> 11 ))
((# Loaathash_result += Loaathash_result << 15 ))
}
# strip comments (and leading/trailing whitespace if IFS is set) from
# any file(s) given as argument, or stdin if none, and spew to stdout
function Lstripcom {