New Appearance of old questions: questions about intercepting Chinese strings in PHP

The following code is used for GB2312 encoding. intercepting Chinese strings is a headache in php (as a mainstream development language, the solution is to determine whether it is a dubyte character based on whether the value is greater than or equal to 128 to avoid garbled characters. However, problems such as Chinese and English mixing and special symbols always exist. Now we write a comprehensive one for your reference only:

Program description:
1. The len parameter is based on Chinese characters. 1len is equal to 2 English characters.
2. If the magic parameter is set to false, the Chinese character and English character count are equivalent.
3. Special character strings that have been encoded with htmlspecialchars ()
4. Properly process the GB2312 entity character mode (& #93232 ;)

Program code:

Function FSubstr ($ title, $ start, $ len = "", $ magic = true)
{
/**
* Powered by Smartpig
* Mailto: d.einstein@263.net
*/

$ Length = 0;
If ($ len = "") $ len = strlen ($ title );

// Judge the starting position as incorrect
If ($ start> 0)
{
$ Cnum = 0;
For ($ I = 0; $ I <$ start; $ I ++)
{
If (ord (substr ($ title, $ I, 1) >=128) $ cnum ++;
}
If ($ cnum % 2! = 0) $ start --;

Unset ($ cnum );
}

If (strlen ($ title) <= $ len) return substr ($ title, $ start, $ len );

$ Alen = 0;
$ Blen = 0;

$ Realnum = 0;

For ($ I = $ start; $ I <strlen ($ title); $ I ++)
{
$ Ctype = 0;
$ Cstep = 0;
$ Cur = substr ($ title, $ I, 1 );
If ($ cur = "&")
{
If (substr ($ title, $ I, 4) = "& lt ;")
{
$ Cstep = 4;
$ Length + = 4;
$ I + = 3;
$ Realnum ++;
If ($ magic)
{
$ Alen ++;
}
}
Else if (substr ($ title, $ I, 4) = "& gt ;")
{
$ Cstep = 4;
$ Length + = 4;
$ I + = 3;
$ Realnum ++;
If ($ magic)
{
$ Alen ++;
}
}
Else if (substr ($ title, $ I, 5) = "& amp ;")
{
$ Cstep = 5;
$ Length + = 5;
$ I + = 4;
$ Realnum ++;
If ($ magic)
{
$ Alen ++;
}
}
Else if (substr ($ title, $ I, 6) = "& quot ;")
{
$ Cstep = 6;
$ Length + = 6;
$ I + = 5;
$ Realnum ++;
If ($ magic)
{
$ Alen ++;
}
}
Else if (substr ($ title, $ I, 6) = "& #039 ;")
{
$ Cstep = 6;
$ Length + = 6;
$ I + = 5;
$ Realnum ++;
If ($ magic)
{
$ Alen ++;
}
}
Else if (preg_match ("/& # (d +);/I", substr ($ title, $ I, 8), $ match ))
{
$ Cstep = strlen ($ match [0]);
$ Length + = strlen ($ match [0]);
$ I + = strlen ($ match [0])-1;
$ Realnum ++;
If ($ magic)
{
$ Blen ++;