Call / Return Macros in Redcode, a Possible Solution

Here's one solution to the call / ret problem in Redcode. Unfortunately the offsets in multi-line-equates can be slightly out. In this solution, the offsets are adjusted the first time the call is executed.  Here's how it works:

call routine compiles as follows:

        mov    #2-return, <stack ; save return address
        jmp    callsub,   1+routine ; jump to callsub which adjusts the address
                                    ; b-field pointer is either correct or out by 1

callsub then adjusts the pointer if necessary and moves it to the a-field of the jmp:

         mov    #2-return, <stack ; save return address
         jmp    routine,   1+routine ; jump to routine, a-field is correct

The jmp now contains the correct offset and jumps directly to routine in future.

Here's the code:

stack   dat    0

call    equ    mov    #2-return, <stack
        equ    jmp    callsub,   1+

ret     equ    jmp    return

return  mov.b  >stack,    #0
        jmp    @return

callsub mov.b  @stack,    #0
        add    #return-callsub, callsub
        mov.ba <callsub,  @callsub
        slt.b  @callsub,  #CORESIZE/2
        jmp    @callsub
        djn.a  @callsub,  @callsub