Re: Using C as a back end

Randall Hyde <rhyde@cs.ucr.edu> wrote:
> Tom Payne at thp@cs.ucr.edu wrote on 10/31/00 12:39 PM:


>> For many applications, indirect jumps (computed gotos) are essential.
[...]
>> [Once again, an indirect jump is, in Fortran-ese, an assigned goto.
>> Or if you speak Cobol, it's an ALTERed goto. -John]


> In Tom's defense, I'd point out that you could create an array of
> these pointers and do the equivalent of a FORTRAN assigned GOTO
> by indexing into the array. Arguably a bit more flexible than
> a switch statement.


Good point. The point I was making went in the opposite direction,
namely, one can use a switch-based hack to emulate gcc's indirect goto
(assigned goto, altered goto, or whatever) within standard C. Here's
the general idea:


      // gcc // standard C equivalent
                                                                  #define LABEL enum pseudolabel
                                                                  #define GOTO(X) target = X; goto target
                                                                  LABEL { L1, L2 };
                                                                  LABEL target;
      ... ...
      void* p; LABEL p;
      ... ...
      L1: ... L1: ...
      ... ...
      ... ...
      L2: ... L2: ...
      ... ...
      p =&& whatever ? L1 : L2; p = whatever ? L1 : L2;
      ... ...
      goto* p; GOTO(p);
      ... ...
                                                                  target: switch ( target ) {
                                                                      case L1: goto L1;
                                                                      case L2: goto L2;
                                                                  }


Tom Payne

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