SWAP     CSECT ,                   control section start
         BAKR  14,0                stack caller's registers
         LR    12,15               entry point address to reg.12
         USING SWAP,12             use as base
         MVC   A,=C'5678____'      init field A
         MVC   B,=C'____1234'      init field B
         LA    2,L                 address of length field in reg.2
         WTO   TEXT=(2)            Write To Operator, results in:
*                                  +5678________1234
         XC    A,B                 XOR A,B
         XC    B,A                 XOR B,A
         XC    A,B                 XOR A,B. A holds B, B holds A
         WTO   TEXT=(2)            Write To Operator, results in:
*                                  +____12345678____
         PR    ,                   return to caller
         LTORG ,                   literals displacement
L        DC    H'16'               halfword containg decimal 16
A        DS    CL8                 field A, 8 bytes
B        DS    CL8                 field B, 8 bytes
         END   SWAP                program end