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| author | Yves Orton <demerphq@gmail.com> | 2012-12-03 11:49:00 +0100 |
|---|---|---|
| committer | Yves Orton <demerphq@gmail.com> | 2012-12-03 11:49:00 +0100 |
| commit | 8c9e24c7f6088cb5fe0779c2c11c1fb4ca8ae693 (patch) | |
| tree | 581f3bfeccb0e1921e7ab9ddd401971face6ea43 /hv.h | |
| parent | c1abd561a0a322ca22ba5ef8301a708c37336afb (diff) | |
| download | perl-8c9e24c7f6088cb5fe0779c2c11c1fb4ca8ae693.tar.gz | |
Make it possible to simulate old style one-at-a-time hashing
With a 0 seed and ONE_AT_A_TIME_OLD hashing enabled one can simulate
older perls (with the exception there is no rehashing at play).
This includes a modest tweak to reduce ops per character by comparing
the string pointer to the end of the string, instead of maintaining
a position counter.
Diffstat (limited to 'hv.h')
| -rw-r--r-- | hv.h | 33 |
1 files changed, 25 insertions, 8 deletions
@@ -143,11 +143,19 @@ struct xpvhv { #define PERL_HASH_FUNC_MURMUR3 #define PERL_HASH_FUNC_SIPHASH #define PERL_HASH_FUNC_ONE_AT_A_TIME +#define PERL_HASH_FUNC_ONE_AT_A_TIME_OLD #define PERL_HASH_FUNC_BUZZHASH16 */ -#if !(defined(PERL_HASH_FUNC_SDBM) || defined(PERL_HASH_FUNC_DJB2) || defined(PERL_HASH_FUNC_SUPERFAST) \ - || defined(PERL_HASH_FUNC_MURMUR3) || defined(PERL_HASH_FUNC_ONE_AT_A_TIME) || defined(PERL_HASH_FUNC_BUZZHASH16)) +#if !( 0 \ + || defined(PERL_HASH_FUNC_SDBM) \ + || defined(PERL_HASH_FUNC_DJB2) \ + || defined(PERL_HASH_FUNC_SUPERFAST) \ + || defined(PERL_HASH_FUNC_MURMUR3) \ + || defined(PERL_HASH_FUNC_ONE_AT_A_TIME) \ + || defined(PERL_HASH_FUNC_ONE_AT_A_TIME_OLD) \ + || defined(PERL_HASH_FUNC_BUZZHASH16) \ + ) #define PERL_HASH_FUNC_MURMUR3 #endif @@ -627,11 +635,20 @@ struct xpvhv { (hash) = hash_PeRlHaSh;\ } STMT_END -#elif defined(PERL_HASH_FUNC_ONE_AT_A_TIME) -/* DEFAULT/HISTORIC HASH FUNCTION */ -#define PERL_HASH_FUNC "ONE_AT_A_TIME" +#elif defined(PERL_HASH_FUNC_ONE_AT_A_TIME) || defined(PERL_HASH_FUNC_ONE_AT_A_TIME_OLD) + #define PERL_HASH_SEED_BYTES 4 +#ifdef PERL_HASH_FUNC_ONE_AT_A_TIME +/* new version, add the length to the seed so that adding characters changes the "seed" being used. */ +#define PERL_HASH_FUNC "ONE_AT_A_TIME" +#define MIX_SEED_AND_LEN(seed,len) (seed + len) +#else +/* old version, just use the seed. - not recommended */ +#define PERL_HASH_FUNC "ONE_AT_A_TIME_OLD" +#define MIX_SEED_AND_LEN(seed,len) (seed) +#endif + /* FYI: This is the "One-at-a-Time" algorithm by Bob Jenkins * from requirements by Colin Plumb. * (http://burtleburtle.net/bob/hash/doobs.html) */ @@ -639,9 +656,9 @@ struct xpvhv { STMT_START { \ const char * const s_PeRlHaSh_tmp = (str); \ const unsigned char *s_PeRlHaSh = (const unsigned char *)s_PeRlHaSh_tmp; \ - I32 i_PeRlHaSh = len; \ - U32 hash_PeRlHaSh = PERL_HASH_SEED_U32 ^ len; \ - while (i_PeRlHaSh--) { \ + const unsigned char *end_PeRlHaSh = (const unsigned char *)s_PeRlHaSh_tmp + (len); \ + U32 hash_PeRlHaSh = MIX_SEED_AND_LEN(PERL_HASH_SEED_U32, len); \ + while (s_PeRlHaSh < end_PeRlHaSh) { \ hash_PeRlHaSh += (U8)*s_PeRlHaSh++; \ hash_PeRlHaSh += (hash_PeRlHaSh << 10); \ hash_PeRlHaSh ^= (hash_PeRlHaSh >> 6); \ |