C routine to convert UTF-8 to UCS2

This simple routine takes input of a UTF-8 Unicode character in the variable input and returns its equivalent in the UCS2 encoding. The second variable end_ptr, is set to one byte beyond the bytes read to form the next character.

/* Convert a UTF-8 encoded character in "input" into a number. This
   function returns the unicode value of the UTF-8 character if
   successful, and -1 if not successful. "end_ptr" is set to the next
   character after the read character on success. "end_ptr" is set to
   the start of input on failure. "end_ptr" may not be null. */

int utf8_to_ucs2 (const unsigned char * input, const unsigned char ** end_ptr)
{
    *end_ptr = input;
    if (input[0] == 0)
        return -1;
    if (input[0] < 0x80) {
        * end_ptr = input + 1;
        return input[0];
    }
    if ((input[0] & 0xE0) == 0xE0) {
        if (input[1] == 0 || input[2] == 0)
            return -1;
        * end_ptr = input + 3;
        return
            (input[0] & 0x0F)<<12 |
            (input[1] & 0x3F)<<6  |
            (input[2] & 0x3F);
    }
    if ((input[0] & 0xC0) == 0xC0) {
        if (input[1] == 0)
            return -1;
        * end_ptr = input + 2;
        return
            (input[0] & 0x1F)<<6  |
            (input[1] & 0x3F);
    }
    return -1;
}