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xstrstr: speed up analysis by avoiding string comparisons

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With large input one should see cut 15% for overall run time.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
This commit is contained in:
Sami Kerola 2013-08-31 00:30:28 +01:00
parent d70b08244f
commit 06ffa5ed04
5 changed files with 102 additions and 98 deletions
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114
src/other.c
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@ -148,53 +148,103 @@ double get_range_size(const struct range_t *r)
}
}
/*! \fn xstrstr(const char *restrict a, const char *restrict b, const int len)
* \brief Compare two strings. Similar to strcmp, but tuned to be
* quicker which is possible because input data is known to have certain
* structure.
/*! \fn xstrstr(const char *restrict str)
* \brief Categorize dhcpd.leases line.
*
* \param a String which is been compared, e.g., a haystack.
* \param b Constant string which is hoped to found, e.g., a needle.
* \param len Stop point in characters when comparison must be ended.
* \return Zero if strings differ, one if they are the same. */
* \param str A line from dhcpd.conf
* \return prefix_t enum value
*/
int
#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
__attribute__ ((hot))
#endif
xstrstr(const char *restrict a, const char *restrict b, const int len)
xstrstr(const char *restrict str)
{
int i;
size_t len;
/* Needed when dhcpd.conf has zero range definitions. */
if (config.dhcp_version == VERSION_UNKNOWN) {
if (!strcmp(prefixes[VERSION_4][PREFIX_LEASE], a)) {
if (strncmp("lease ", str, 6)) {
config.dhcp_version = VERSION_4;
return true;
}
if (!strcmp(prefixes[VERSION_6][PREFIX_LEASE], a)) {
return PREFIX_LEASE;
} else if (strncmp(" iaaddr ", str, 9)) {
config.dhcp_version = VERSION_6;
return true;
return PREFIX_LEASE;
}
return false;
return NUM_OF_PREFIX;
}
/* two spaces are very common in lease file, after them
* nearly everything differs */
if (likely(a[2] != b[2])) {
return false;
if ((config.dhcp_version == VERSION_4 && str[2] == 'b')
|| (config.dhcp_version == VERSION_6 && str[4] == 'b')
|| str[2] == 'h') {
len = strlen(str);
} else {
len = 0;
}
/* " binding state " == 16 chars, this will skip right
* to first differing line. */
if (17 < len && a[17] != b[17]) {
return false;
}
/* looking good, double check the whole thing... */
for (i = 0; a[i] != '\0' && b[i] != '\0'; i++) {
if (a[i] != b[i]) {
return false;
if (15 < len && config.dhcp_version == VERSION_4) {
switch (str[16]) {
case 'f':
if (!strncmp(" binding state free;", str, 21))
return PREFIX_BINDING_STATE_FREE;
break;
case 'a':
if (!strncmp(" binding state active;", str, 23))
return PREFIX_BINDING_STATE_ACTIVE;
if (!strncmp(" binding state abandoned;", str, 25))
return PREFIX_BINDING_STATE_ABANDONED;
break;
case 'e':
if (!strncmp(" binding state expired;", str, 24))
return PREFIX_BINDING_STATE_EXPIRED;
break;
case 'r':
if (!strncmp(" binding state released;", str, 25))
return PREFIX_BINDING_STATE_RELEASED;
break;
case 'b':
if (!strncmp(" binding state backup;", str, 23))
return PREFIX_BINDING_STATE_BACKUP;
break;
case 'n':
if (!strncmp(" hardware ethernet", str, 19))
return PREFIX_HARDWARE_ETHERNET;
break;
}
} else if (17 < len /* && config.dhcp_version == VERSION_6 */ ) {
switch (str[18]) {
case 'f':
if (!strncmp(" binding state free;", str, 23))
return PREFIX_BINDING_STATE_FREE;
break;
case 'a':
if (!strncmp(" binding state active;", str, 25))
return PREFIX_BINDING_STATE_ACTIVE;
if (!strncmp(" binding state abandoned;", str, 27))
return PREFIX_BINDING_STATE_ABANDONED;
break;
case 'e':
if (!strncmp(" binding state expired;", str, 26))
return PREFIX_BINDING_STATE_EXPIRED;
break;
case 'r':
if (!strncmp(" binding state released;", str, 27))
return PREFIX_BINDING_STATE_RELEASED;
break;
case 'b':
if (!strncmp(" binding state backup;", str, 25))
return PREFIX_BINDING_STATE_BACKUP;
break;
case 'n':
if (!strncmp(" hardware ethernet", str, 19))
return PREFIX_HARDWARE_ETHERNET;
break;
}
}
return true;
if (config.dhcp_version == VERSION_4 && !strncmp("lease ", str, 6)) {
return PREFIX_LEASE;
} else if (config.dhcp_version == VERSION_6
&& !strncmp(" iaaddr ", str, 9)) {
return PREFIX_LEASE;
}
return NUM_OF_PREFIX;
}
/*! \brief Return a double floating point value.