用MIPS实现字符串操作子程序？

vaqeteart

想找一个用MIPS实现的下面字符串程序，找了一下午，没有，哪位帮帮忙？谢谢！！
1.strcat (s1,s2)
appends a copy of string s2,including the terminating null
      character, to the end of string s 1. The function returns a pointer to the null-
        terminated result. The initial character of s2  overrides the null character at the
        end of s 1.
2.strcmp(sl,s2)
compares two strings byte-by-byte.  The function returns  an
      integer greater than, equal to, or less than 0, if the string pointed to by s 1  is
      greater than, equal to, or less than the string pointed to by s2  respectively.
      The sign of a non-zero return value is determined by the sign of the difference
      between the values of the first pair of bytes that differ in the strings being
      compared. Bytes following a null byte are not compared.
3.strcmpi(s1,s2)
this function performs in the same manner as strcmp, except that
      it considers both the lower and upper case version of a letter to be the same
      character. Hint: study the ASCII table in binary.
4.strstr(sl,s2)
locates the first occurrence of the string s2  in the string s1
      (excluding the terminating null character). The address of the start of the
        located stringy (or 0 if the stringy is not found) is returned.