diff options
| author | John Naylor | 2024-01-21 12:19:14 +0000 |
|---|---|---|
| committer | John Naylor | 2024-02-06 07:39:36 +0000 |
| commit | 9ed3ee5001b6a2d4cb0166eb8f12a457f30aaca4 (patch) | |
| tree | 67ea542a24cea71cad13cc64ca36bd425d7685f7 /src | |
| parent | 1f61680327c962d5bafdbf6a04ad9bb0f7232f92 (diff) | |
Simplify initialization of incremental hash state
The standalone functions fasthash{32,64} use length for two purposes:
how many bytes to hash, and how to perturb the internal seed.
Developers using the incremental interface may not know the length
ahead of time (e.g. for C strings). In this case, it's advised to
pass length to the finalizer, but initialization still needed some
length up front, in the form of a placeholder macro.
Separate the concerns by having the standalone functions perturb the
internal seed themselves from their own length parameter, allowing
to remove "len" from fasthash_init(), as well as the placeholder macro.
Discussion: https://postgr.es/m/CANWCAZbTUk2LOyhsFo33gjLyLAHZ7ucXCi5K9u%3D%2BPtnTShDKtw%40mail.gmail.com
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/catalog/namespace.c | 2 | ||||
| -rw-r--r-- | src/include/common/hashfn_unstable.h | 19 |
2 files changed, 9 insertions, 12 deletions
diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c index b610aa62423..8df30b24401 100644 --- a/src/backend/catalog/namespace.c +++ b/src/backend/catalog/namespace.c @@ -256,7 +256,7 @@ spcachekey_hash(SearchPathCacheKey key) fasthash_state hs; int sp_len; - fasthash_init(&hs, FH_UNKNOWN_LENGTH, 0); + fasthash_init(&hs, 0); hs.accum = key.roleid; fasthash_combine(&hs); diff --git a/src/include/common/hashfn_unstable.h b/src/include/common/hashfn_unstable.h index 3d927e1fb18..63ebe295c5f 100644 --- a/src/include/common/hashfn_unstable.h +++ b/src/include/common/hashfn_unstable.h @@ -65,15 +65,12 @@ * in fasthash_accum_cstring() : * * fasthash_state hs; - * fasthash_init(&hs, FH_UNKNOWN_LENGTH, 0); + * fasthash_init(&hs, 0); * len = fasthash_accum_cstring(&hs, *str); * ... * return fasthash_final32(&hs, len); * - * Here we pass FH_UNKNOWN_LENGTH as a convention, since passing zero - * would zero out the internal seed as well. fasthash_accum_cstring() - * returns the length of the string, which is computed on-the-fly while - * mixing the string into the hash. Experimentation has found that + * The length is computed on-the-fly. Experimentation has found that * SMHasher fails unless we incorporate the length, so it is passed to * the finalizer as a tweak. */ @@ -89,20 +86,17 @@ typedef struct fasthash_state #define FH_SIZEOF_ACCUM sizeof(uint64) -#define FH_UNKNOWN_LENGTH 1 /* * Initialize the hash state. * - * 'len' is the length of the input, if known ahead of time. - * If that is not known, pass FH_UNKNOWN_LENGTH. * 'seed' can be zero. */ static inline void -fasthash_init(fasthash_state *hs, int len, uint64 seed) +fasthash_init(fasthash_state *hs, uint64 seed) { memset(hs, 0, sizeof(fasthash_state)); - hs->hash = seed ^ (len * 0x880355f21e6d1965); + hs->hash = seed ^ 0x880355f21e6d1965; } /* both the finalizer and part of the combining step */ @@ -328,7 +322,10 @@ fasthash64(const char *k, int len, uint64 seed) { fasthash_state hs; - fasthash_init(&hs, len, seed); + fasthash_init(&hs, 0); + + /* re-initialize the seed according to input length */ + hs.hash = seed ^ (len * 0x880355f21e6d1965); while (len >= FH_SIZEOF_ACCUM) { |