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authorYves Orton <demerphq@gmail.com>2012-11-17 14:12:04 +0100
committerYves Orton <demerphq@gmail.com>2012-11-17 19:19:43 +0100
commit7dc8663964c66a698d31bbdc8e8abed69bddeec3 (patch)
tree92f39aa5770c2f401bbe134db921d68cbe4f758a /perlvars.h
parent867b16b50f413adfdb2addcab33ad1d6e61da9d5 (diff)
downloadperl-7dc8663964c66a698d31bbdc8e8abed69bddeec3.tar.gz
Hash Function Change - Murmur hash and true per process hash seed
This patch does the following: *) Introduces multiple new hash functions to choose from at build time. This includes Murmur-32, SDBM, DJB2, SipHash, SuperFast, and One-at-a-time. Currently this is handled by muning hv.h. Configure support hopefully to follow. *) Changes the default hash to Murmur hash which is faster than the old default One-at-a-time. *) Rips out the old HvREHASH mechanism and replaces it with a per-process random hash seed. *) Changes the old PL_hash_seed from an interpreter value to a global variable. This means it does not have to be copied during interpreter setup or cloning. *) Changes the format of the PERL_HASH_SEED variable to a hex string so that hash seeds longer than fit in an integer are possible. *) Changes the return of Hash::Util::hash_seed() from a number to a string. This is to accomodate hash functions which have more bits than can be fit in an integer. *) Adds new functions to Hash::Util to improve introspection of hashes -) hash_value() - returns an integer hash value for a given string. -) bucket_info() - returns basic hash bucket utilization info -) bucket_stats() - returns more hash bucket utilization info -) bucket_array() - which keys are in which buckets in a hash More details on the new hash functions can be found below: Murmur Hash: (v3) from google, see http://code.google.com/p/smhasher/wiki/MurmurHash3 Superfast Hash: From Paul Hsieh. http://www.azillionmonkeys.com/qed/hash.html DJB2: a hash function from Daniel Bernstein http://www.cse.yorku.ca/~oz/hash.html SDBM: a hash function sdbm. http://www.cse.yorku.ca/~oz/hash.html SipHash: by Jean-Philippe Aumasson and Daniel J. Bernstein. https://www.131002.net/siphash/ They have all be converted into Perl's ugly macro format. I have not done any rigorous testing to make sure this conversion is correct. They seem to function as expected however. All of them use the random hash seed. You can force the use of a given function by defining one of PERL_HASH_FUNC_MURMUR PERL_HASH_FUNC_SUPERFAST PERL_HASH_FUNC_DJB2 PERL_HASH_FUNC_SDBM PERL_HASH_FUNC_ONE_AT_A_TIME Setting the environment variable PERL_HASH_SEED_DEBUG to 1 will make perl output the current seed (changed to hex) and the hash function it has been built with. Setting the environment variable PERL_HASH_SEED to a hex value will cause that value to be used at the seed. Any missing bits of the seed will be set to 0. The bits are filled in from left to right, not the traditional right to left so setting it to FE results in a seed value of "FE000000" not "000000FE". Note that we do the hash seed initialization in perl_construct(). Doing it via perl_alloc() (via init_tls) causes problems under threaded builds as the buffers used for reentrant srand48 functions are not allocated. See also the p5p mail "Hash improvements blocker: portable random code that doesnt depend on a functional interpreter", Message-ID: <CANgJU+X+wNayjsNOpKRqYHnEy_+B9UH_2irRA5O3ZmcYGAAZFQ@mail.gmail.com>
Diffstat (limited to 'perlvars.h')
-rw-r--r--perlvars.h3
1 files changed, 3 insertions, 0 deletions
diff --git a/perlvars.h b/perlvars.h
index 20c3882fc8..68471a0b80 100644
--- a/perlvars.h
+++ b/perlvars.h
@@ -231,3 +231,6 @@ PERLVAR(G, sv_placeholder, SV)
#if defined(MYMALLOC) && defined(USE_ITHREADS)
PERLVAR(G, malloc_mutex, perl_mutex) /* Mutex for malloc */
#endif
+
+PERLVARI(G, hash_seed_set, bool, FALSE) /* perl.c */
+PERLVARA(G, hash_seed, 8, unsigned char) /* and hv.h */