clang jmp-cflow.c -Weverything -Wno-shadow -Wno-unused-variable -Wno-missing-noreturn -Wno-reserved-id-macro -Wno-unused-macros -Werror

more-jmp.c

#include <setjmp.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

#define BEGIN_BLOCK                             \
  {                                             \
  volatile uint8_t orig_exc_i = exc_i;          \
  volatile uint8_t exc_i = orig_exc_i + 1;      \
  switch(setjmp(exc[exc_i].catcher)) {          \
  case 0:                                       \
  case 1:

#define __E_CATCHER(off) exc[exc_i-off].catcher
#define __E_RESUMER(off) exc[exc_i-off].resumer

#define __E_THROW(n)    if(setjmp(__E_RESUMER(0)) == 0) { longjmp(__E_CATCHER(0), n); }
#define __E_THROW_UP(n) if(setjmp(__E_RESUMER(1)) == 0) { longjmp(__E_CATCHER(1), n); }
#define __E_CATCH(n)    break; case (n):

#define END_BLOCK                               \
  break;                                        \
  default:                                      \
  fprintf(stderr, "missing CATCH for THROW - did you mean to use THROW_UP? aborting...\n"); \
  abort();                                      \
  }                                             \
  }

#define THROW(n)    __E_THROW((n)+2)
#define CATCH(n)    __E_CATCH((n)+2)
#define RESTART     longjmp(__E_CATCHER(0), 1)
#define RESUME      longjmp(__E_RESUMER(0), 1)

#define THROW_UP(n) __E_THROW_UP((n)+2)
#define RESTART_UP  longjmp(__E_CATCHER(1), 1)
#define RESUME_UP   longjmp(__E_RESUMER(1), 1)

#define BEGIN_E_FUNC(ty, name, ...)             \
  __attribute__((always_inline))                \
  __attribute__((noreturn))                     \
  static inline ty name(uint8_t exc_i, __VA_ARGS__) {

#define END_E_FUNC                              \
  fprintf(stderr, "control has reached end of E_FUNC.  aborting...\n"); \
  abort();                                      \
  }

#define CALL_E_FUNC(name, ...) name(exc_i, __VA_ARGS__)


static struct {
  jmp_buf catcher;
  jmp_buf resumer;
} exc[255];

/* THROWs true or false */
BEGIN_E_FUNC(void, check_numbers, int a, int b)
  THROW(a == b);

  printf("\nTry again, but enter two equal numbers this time!\n\n");
  RESTART;
END_E_FUNC

BEGIN_E_FUNC(void, e_main, int *ret)
  volatile int a, b;

  BEGIN_BLOCK
    printf("Enter a number:\n");
    scanf("%d", &a);
    printf("Enter a second number:\n");
    scanf("%d", &b);
    CALL_E_FUNC(check_numbers, a, b);
  CATCH(true)
    printf("%d == %d\n", a, b);
    THROW_UP(256);
    printf("yay!\n");
    *ret = 0;
    THROW_UP(42);
  CATCH(false)
    printf("%d != %d\n", a, b);
    RESUME;
  END_BLOCK
END_E_FUNC

int main(void) {
  uint8_t exc_i = 0;
  int ret = 1;
  switch(setjmp(__E_CATCHER(0))) {
  case 0:
  case 1:
    e_main(exc_i, &ret);
  case 42:
    printf("returning\n");
    break;
  default:
    fprintf(stderr, "uncaught exception!\n");
    longjmp(__E_RESUMER(0), 1);
  }
  return ret;
}