分析PHP的similar_text函數

//比較字符串,傳回兩個字符串第一個相同字元的區域
static void php_similar_str(const char *txt1, int len1, const char *txt2, int len2, int *pos1, int *pos2, int *max)
{
char *p, *q;
char *end1 = (char *) txt1 + len1;
char *end2 = (char *) txt2 + len2;
int l;

*max = 0;
//遍歷字符串
for (p = (char *) txt1; p < end1; p++) {
for (q = (char *) txt2; q < end2; q++) {
for (l = 0; (p + l < end1) && (q + l < end2) && (p[l] == q[l]); l++);
if (l > *max) {
//儲存相同區域資訊
*max = l;
*pos1 = p - txt1;
*pos2 = q - txt2;
}
}
}
}

//遞迴函數,比較txt1和txt2的相同字元數量
static int php_similar_char(const char *txt1, int len1, const char *txt2, int len2)
{
int sum;
int pos1, pos2, max;

php_similar_str(txt1, len1, txt2, len2, &pos1, &pos2, &max);
if ((sum = max)) {//這樣寫有什麼意義?????!!!!!

//遞歸上次不同部分的前部
if (pos1 && pos2) {
sum += php_similar_char(txt1, pos1, txt2, pos2);
}

//遞歸上次不同部分的後部
if ((pos1 + max < len1) && (pos2 + max < len2)) {
sum += php_similar_char(txt1 + pos1 + max, len1 - pos1 - max,
txt2 + pos2 + max, len2 - pos2 - max);
}
}

//傳回本次比較後的相同字元數量
return sum;
}

//PHP函數本身，一堆宏，做了些串轉換和回傳值換算,主功能由上面兩個函數做了。
PHP_FUNCTION(similar_text)
{
zval **t1, **t2, **percent;
int ac = ZEND_NUM_ARGS();
int sim;

if (ac < 2 || ac > 3 || zend_get_parameters_ex(ac, &t1, &t2, &percent) == FAILURE) {
WRONG_PARAM_COUNT;
}

convert_to_string_ex(t1);
convert_to_string_ex(t2);

if (ac > 2) {
convert_to_double_ex(percent);
}

if (Z_STRLEN_PP(t1) + Z_STRLEN_PP(t2) == 0) {
if (ac > 2) {
Z_DVAL_PP(percent) = 0;
}

RETURN_LONG(0);
}

sim = php_similar_char(Z_STRVAL_PP(t1), Z_STRLEN_PP(t1), Z_STRVAL_PP(t2), Z_STRLEN_PP(t2));

if (ac > 2) {
Z_DVAL_PP(percent) = sim * 200.0 / (Z_STRLEN_PP(t1) + Z_STRLEN_PP(t2));
}

RETURN_LONG(sim);
}

所有看出similar_text是根據ASCII做比較的，是不考慮詞組問題的。

測試了一下，結果如下：

int main(int argc, char *argv[])
{
char *str1="weican wuxin";
char *str2="wuxin weican";
int pos1,pos2,max;

php_similar_str(str1,strlen(str1),str2,strlen(str2),&pos1,&pos2,&max);
printf("php_similar_str:%d,%d=%dn",pos1,pos2,max);

max=php_similar_char(str1,strlen(str1),str2,strlen(str2));
printf("php_similar_char:%dn",max);

system("PAUSE");
return 0;
}

php_similar_str:0,6=6
php_similar_char:6

char *str1="TCP協定通訊工作原a理";
char *str2="TCPa協定通訊運作方式";

php_similar_str:3,4=14
php_similar_char:19