分析PHP的similar_text函数

  //比较字串,返回两个字串第一个相同字符的区域
  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;
  //遍历字串
  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) {
   //保存相同区域信息
   *max = l;
   *pos1 = p - txt1;
   *pos2 = q - txt2;
   }
   }
  }
  }
  //递归函数,比较txt1和txt2的相同字符数量
  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)) {//这样写有什么意义?????!!!!!
   //递归上次不同部分的前部
   if (pos1 && pos2) {
   sum += php_similar_char(txt1, pos1, txt2, pos2);
   }
   //递归上次不同部分的后部
   if ((pos1 + max < len1) && (pos2 + max < len2)) {
   sum += php_similar_char(txt1 + pos1 + max, len1 - pos1 - max,
   txt2 + pos2 + max, len2 - pos2 - max);
   }
  }
  //返回本次比较后的相同字符数量
  return sum;
  }
  //PHP函数本身,一堆宏,做了些串转换和返回值换算,主功能由上面两个函数做了。
  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是根据ASCII做比较的,是不考虑词组问题的。
  测试了一下,结果如下:
  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=%d\n",pos1,pos2,max);
   max=php_similar_char(str1,strlen(str1),str2,strlen(str2));
   printf("php_similar_char:%d\n",max);
   system("PAUSE");
   return 0;
  }
  php_similar_str:0,6=6
  php_similar_char:6
  char *str1="TCP协议通讯工作原a理";
  char *str2="TCPa协议通讯工作原理";
  php_similar_str:3,4=14
  php_similar_char:19