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Replace hash function from bcache with fast_hash

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This function is not just slower than xxhash, it is slower than
even libiberty's iterative_hash, so there does not seem to be
a reason for it to exist.

------------------------------------------------------------
Benchmark                     Time           CPU Iterations
------------------------------------------------------------
BM_xxh3                      11 ns         11 ns   66127192
BM_xxh32                     19 ns         19 ns   36792609
BM_xxh64                     16 ns         16 ns   42941328
BM_city32                    26 ns         26 ns   27028370
BM_city64                    17 ns         17 ns   40472793
BM_iterative_hash            77 ns         77 ns    9088854
BM_bcache_hash              125 ns        125 ns    5599232

gdb/ChangeLog:

2019-12-03  Christian Biesinger  <cbiesinger@google.com>

	* bcache.c (hash): Remove.
	(hash_continue): Remove.
	* bcache.h (hash): Remove.
	(hash_continue): Remove.
	(struct bcache) <ctor>: Update.
	* psymtab.c (psymbol_hash): Update.
	* stabsread.c (hashname): Update.
	* utils.h (fast_hash): Add an argument for a start value,
	defaulting to zero.

Change-Id: I107f013eda5fdd3293326b5a206be43155dae0f8
This commit is contained in:
Christian Biesinger
2019-12-02 18:58:35 -06:00
parent 82f910ea9c
commit 4cbd39b289
6 changed files with 32 additions and 44 deletions
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25
gdb/bcache.c
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@@ -51,31 +51,6 @@ struct bstring
d;
};
/* The old hash function was stolen from SDBM. This is what DB 3.0
uses now, and is better than the old one. */
unsigned long
hash(const void *addr, int length)
{
return hash_continue (addr, length, 0);
}
/* Continue the calculation of the hash H at the given address. */
unsigned long
hash_continue (const void *addr, int length, unsigned long h)
{
const unsigned char *k, *e;
k = (const unsigned char *)addr;
e = k+length;
for (; k< e;++k)
{
h *=16777619;
h ^= *k;
}
return (h);
}
/* Growing the bcache's hash table. */