Skip to content

Improve performance of mbfl_name2encoding() by using perfect hashing #12707

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Nov 17, 2023
Merged

Improve performance of mbfl_name2encoding() by using perfect hashing #12707

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 2 additions & 0 deletions UPGRADING
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -227,3 +227,5 @@ PHP 8.4 UPGRADE NOTES
* mb_strcut() is much faster now for UTF-8 and UTF-16 strings.

* get_browser() is much faster now, up to 1.5x - 2.5x for some test cases.

* Looking up mbstring encoding names is much faster now.
205 changes: 202 additions & 3 deletions ext/mbstring/libmbfl/mbfl/mbfl_encoding.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -144,13 +144,212 @@ static const mbfl_encoding *mbfl_encoding_ptr_list[] = {
NULL
};

/* The following perfect hashing table was amended from gperf, and hashing code was generated using gperf.
* The table was amended to refer to the table above such that it is lighter for the data cache.
* Command used: gperf encodings.txt --readonly-tables --null-strings --ignore-case
* The encodings.txt contains all the contents of the name fields of the mbfl_encoding_ptr_list table. */

static const int8_t mbfl_encoding_ptr_list_after_hashing[187] = {
-1, -1, -1,
65,
23,
9,
-1,
60,
36,
-1, -1,
58,
42,
-1, -1,
18,
27,
77,
26,
40,
72,
12,
10,
2,
31,
-1, -1,
75,
74,
33,
45,
-1,
67,
13,
-1,
51,
53,
11,
1,
-1,
48,
56,
-1,
38,
20,
46,
54,
-1,
14,
24,
44,
39,
43,
-1,
30,
49,
57,
76,
-1, -1,
68,
73,
7,
16,
-1,
35,
66,
-1, -1, -1,
47,
55,
-1, -1, -1,
63,
15,
8,
17,
-1,
21,
70,
-1,
29,
5,
6,
61,
-1, -1,
71,
52,
3,
37,
-1, -1,
28,
-1, -1, -1,
32,
50,
34,
-1, -1, -1,
62,
-1, -1, -1, -1, -1, -1, -1, -1, -1,
59,
0,
-1, -1, -1, -1,
22,
-1, -1, -1, -1, -1, -1, -1, -1, -1,
25,
41,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
19,
-1, -1, -1,
4,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
69,
-1, -1, -1, -1,
64,
};

static unsigned int mbfl_name2encoding_perfect_hash(const char *str, size_t len)
{
static const unsigned char asso_values[] =
{
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 0, 187, 187, 5, 20,
0, 15, 40, 10, 25, 70, 5, 60, 187, 187,
187, 187, 187, 187, 187, 75, 5, 0, 20, 5,
0, 75, 5, 0, 40, 75, 20, 0, 0, 0,
35, 45, 50, 0, 75, 0, 187, 0, 187, 187,
0, 187, 187, 187, 187, 187, 187, 75, 5, 0,
20, 5, 0, 75, 5, 0, 40, 75, 20, 0,
0, 0, 35, 45, 50, 0, 75, 0, 187, 0,
187, 187, 0, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187, 187, 187, 187, 187,
187, 187, 187, 187, 187, 187
};
unsigned int hval = len;

switch (hval)
{
default:
hval += asso_values[(unsigned char)str[6]];
ZEND_FALLTHROUGH;
case 6:
hval += asso_values[(unsigned char)str[5]];
ZEND_FALLTHROUGH;
case 5:
hval += asso_values[(unsigned char)str[4]];
ZEND_FALLTHROUGH;
case 4:
case 3:
hval += asso_values[(unsigned char)str[2]];
ZEND_FALLTHROUGH;
case 2:
case 1:
hval += asso_values[(unsigned char)str[0]];
break;
}
return hval + asso_values[(unsigned char)str[len - 1]];
}

#define NAME_HASH_MIN_NAME_LENGTH 2
#define NAME_HASH_MAX_NAME_LENGTH 23

const mbfl_encoding *mbfl_name2encoding(const char *name)
{
const mbfl_encoding **encoding;
const mbfl_encoding *const *encoding;

/* Sanity check perfect hash for name.
* Never enable this in production, this is only a development-time sanity check! */
#if ZEND_DEBUG && 0
for (encoding = mbfl_encoding_ptr_list; *encoding; encoding++) {
if (strcasecmp((*encoding)->name, name) == 0) {
return *encoding;
size_t name_length = strlen((*encoding)->name);
if (!(name_length <= NAME_HASH_MAX_NAME_LENGTH && name_length >= NAME_HASH_MIN_NAME_LENGTH)) {
fprintf(stderr, "name length is not satisfying bound check: %zu %s\n", name_length, (*encoding)->name);
abort();
}
unsigned int key = mbfl_name2encoding_perfect_hash((*encoding)->name, name_length);
if (mbfl_encoding_ptr_list[mbfl_encoding_ptr_list_after_hashing[key]] != *encoding) {
fprintf(stderr, "mbfl_name2encoding_perfect_hash: key %u %s mismatch\n", key, (*encoding)->name);
abort();
}
}
#endif

/* Use perfect hash lookup for name */
size_t name_len = strlen(name);
if (name_len <= NAME_HASH_MAX_NAME_LENGTH && name_len >= NAME_HASH_MIN_NAME_LENGTH) {
unsigned int key = mbfl_name2encoding_perfect_hash(name, name_len);
if (key <= 186) {
int8_t offset = mbfl_encoding_ptr_list_after_hashing[key];
if (offset >= 0) {
encoding = mbfl_encoding_ptr_list + offset;
if (strcasecmp((*encoding)->name, name) == 0) {
return *encoding;
}
}
}
}

Expand Down