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Optimize Strings_startWith()

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Use strncmp() combined with a strlen() will give better performance
than a strstr in worst case. Especially when the match prefix is a
constant and not a variable.

While we are at it, replace the match() function in linux/Battery.c,
which uses a naive algorithm, with a macro that does better job by
utilizing Strings_startWith().

    $ gcc --version | head -n 1
    gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4
    $ uname -m
    x86_64
    $ size htop.old htop.new
       text   data    bss    dec    hex filename
     137929  15112   3776 156817  26491 htop.old
     137784  15104   3776 156664  263f8 htop.new

Signed-off-by: Kang-Che Sung <explorer09 @ gmail.com>
This commit is contained in:
Explorer09
2016-08-11 10:49:35 +08:00
parent b269eb24b0
commit bf35921abb
4 changed files with 15 additions and 28 deletions
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22
linux/Battery.c
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@ -179,25 +179,6 @@ static inline ssize_t xread(int fd, void *buf, size_t count) {
}
}
/**
* Returns a pointer to the suffix of `str` if its beginning matches `prefix`.
* Returns NULL if the prefix does not match.
* Examples:
* match("hello world", "hello "); -> "world"
* match("hello world", "goodbye "); -> NULL
*/
static inline const char* match(const char* str, const char* prefix) {
for (;;) {
if (*prefix == '\0') {
return str;
}
if (*prefix != *str) {
return NULL;
}
prefix++; str++;
}
}
static void Battery_getSysData(double* level, ACPresence* isOnAC) {
*level = 0;
@ -240,6 +221,8 @@ static void Battery_getSysData(double* level, ACPresence* isOnAC) {
bool full = false;
bool now = false;
while ((line = strsep(&buf, "\n")) != NULL) {
#define match(str,prefix) \
(String_startsWith(str,prefix) ? (str) + strlen(prefix) : NULL)
const char* ps = match(line, "POWER_SUPPLY_");
if (!ps) {
continue;
@ -266,6 +249,7 @@ static void Battery_getSysData(double* level, ACPresence* isOnAC) {
continue;
}
}
#undef match
} else if (entryName[0] == 'A') {
if (*isOnAC != AC_ERROR) {
continue;