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* src/fns.c (hash_string): Speed up on large strings

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This commit is contained in:
Stefan Monnier 2020-12-08 18:08:54 -05:00
parent ca50519900
commit be0f2de179
1 changed files with 33 additions and 10 deletions
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43
src/fns.c
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@ -18,6 +18,7 @@ GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>. */
#include <stdio.h>
#include <config.h>
#include <stdlib.h>
@ -4525,18 +4526,40 @@ sweep_weak_table (struct Lisp_Hash_Table *h, bool remove_entries_p)
EMACS_UINT
hash_string (char const *ptr, ptrdiff_t len)
{
char const *p = ptr;
char const *end = p + len;
unsigned char c;
EMACS_UINT hash = 0;
while (p != end)
if (len < 16)
{
c = *p++;
hash = sxhash_combine (hash, c);
}
char const *p = ptr;
char const *end = p + len;
EMACS_UINT hash = len;
return hash;
while (p < end)
{
unsigned char c = *p++;
hash = sxhash_combine (hash, c);
}
return hash;
}
else
{
EMACS_UINT const *p = (EMACS_UINT const *) ptr;
EMACS_UINT const *end = (EMACS_UINT const *) (ptr + len);
EMACS_UINT hash = len;
/* At most 8 steps. We could reuse SXHASH_MAX_LEN, of course,
* but dividing by 8 is cheaper. */
ptrdiff_t step = max (1, (end - p) >> 3);
/* Beware: `end` might be unaligned, so `p < end` is not always the same
* as `p <= end - 1`. */
while (p <= end - 1)
{
EMACS_UINT c = *p;
p += step;
hash = sxhash_combine (hash, c);
}
return hash;
}
}
/* Return a hash for string PTR which has length LEN. The hash