int count = 0;
    long a = 0L;
    long b = 0L;
    long overflow = 0L;
    long max = 4294967296L;
    long c = 0;

    if (str.length() != 7) {
        System.out.println("- Failed clientcode proof length test: " + str + " -> length: " + str.length());
        return false;
        }

    while (count < str.length() -1) {

        a = c << 4;
        b = str.getBytes()[count];
        c = a ^ b;
        overflow = c >> 32;
        c = c & 0xFFFFFFFF;
        c = c ^ overflow;

        System.out.printf( "a=%15d %45sn", a, Long.toBinaryString( a ));
        System.out.printf( "b=%15d %45sn", b, Long.toBinaryString( b ));
        System.out.printf( "c=%15d %45sn", c, Long.toBinaryString( c ));
        System.out.println( "---------------------------------------------------------------");
        count++;
    }

    if (c > 2147483647) {
        c = c - max;
    } else if (c >= 32768 && c <= 65535) {
        c = c - 65536;
    } else if (c >= 128 && c <= 255) {
        c = c - 256;
    }

    String strTekenreeks = "BCDFGHJKMNPQRSTWXYZ23456789";
//  Java result
//        int intModulus = toIntExact(c) % 27;
    int intModulus = (int)c % 27;
    String strCalculatedChar = strTekenreeks.substring(intModulus, intModulus + 1);
    System.out.printf("Java checksum  : %s, modulo %d=%d, %s, %sn", c, 27, toIntExact(c) % 27, strTekenreeks, strCalculatedChar);

//  T-SQl result
    intModulus = 158510959 % 27;
    strCalculatedChar = strTekenreeks.substring(intModulus, intModulus + 1);
    System.out.printf("T-SQL checksum : %s, modulo %d=%d, %s, %sn", "158510959", 27, toIntExact(158510959) % 27, strTekenreeks, strCalculatedChar);
//
    String strLastChar = str.substring(6, 7);
    if (strLastChar.equals(strCalculatedChar)) {
       System.out.println("- Passed clientcode proof");
       return true;
    } else {
       System.out.println("- Failed clientcode proof: " + str + ", calculated character: " + strCalculatedChar);
       return false;
//           return true;
    }

File: S5WKBCK_testcodeS5WKBCK.pdf
a=              0                                             0
b=             83                                       1010011
c=             83                                       1010011
---------------------------------------------------------------
a=           1328                                   10100110000
b=             53                                        110101
c=           1285                                   10100000101
---------------------------------------------------------------
a=          20560                               101000001010000
b=             87                                       1010111
c=          20487                               101000000000111
---------------------------------------------------------------
a=         327792                           1010000000001110000
b=             75                                       1001011
c=         327739                           1010000000000111011
---------------------------------------------------------------
a=        5243824                       10100000000001110110000
b=             66                                       1000010
c=        5243890                       10100000000001111110010
---------------------------------------------------------------
a=       83902240                   101000000000011111100100000
b=             67                                       1000011
c=       83902307                   101000000000011111101100011
---------------------------------------------------------------
Java binary_checksum()  : 83902307, modulo 27=23, BCDFGHJKMNPQRSTWXYZ23456789, 6
- Failed proof: S5WKBCK, calculated character: 6

T-SQL binary_checksum() : 158510959, modulo 27=7, BCDFGHJKMNPQRSTWXYZ23456789, K
- Passed proof: S5WKBCK, calculated character: K