def StrIndexOf(input_string, substring, startIndex, bitlength):
try:<EOL><INDENT>s = input_string.value<EOL>t = substring.value<EOL>i = startIndex.value<EOL>return BVV(i + s[i:].index(t), bitlength)<EOL><DEDENT>except ValueError:<EOL><INDENT>return BVV(-<NUM_LIT:1>, bitlength)<EOL><DEDENT>
Return True if the concrete value of the input_string ends with suffix
otherwise false.

:param input_string: the string we want to check
:param substring: the substring we want to find the index
:param startIndex: the index to start searching at
:param bitlength: bitlength of the bitvector representing the index of the substring

:return BVV: index of the substring in bit-vector representation or -1 in bitvector representation