Source: /app/hbasic/hbasic/runtime_lib/runtime_stack.h

#define COMP_ALLOC_SIZE 5000

/* runtime stack handling. */
extern RT_VALUE *rt_comp_ptr;		/* top of comp_stack (first empty position) */
extern RT_VALUE *rt_comp_mem;          /* Start of allocated memory. */
extern RT_VALUE *rt_comp_top;          /* Top of allocated memory */
extern long rt_comp_allocated;         /* allocated memory size for rt_comp_ptr */

/* stack for local variables at runtime */
extern char *rt_runtime_stack;
extern char *rt_lvar_stack_ptr;   /* Pointer to current top of stack. */
extern long rt_lvar_allocated;    /* Size of allocated memory */
extern long rt_lvar_topadr;       /* top address (rt_runtime_stack + rt_comp_allocated) */
// pointer to current top of address stack
extern long *rt_address_ptr;	/* Current pointer into address stack. */
extern long *rt_address_mem;   /* Pointer to allocated memory */
extern long *rt_address_top;   /* Top of allocated address stack */
extern long rt_address_allocated;   /* size of allocated address memory. */

/* Stack for pointer to class memory in Interpreter. */
extern long *rt_classstack_mem;       /* Start of memory allocated for classpointer. */
extern long *rt_classstack_ptr;
extern long rt_classstack_allocated;

/* ------------------------------------------------------------- */

/* Initialize or free stack pointer */
short alloc_runtime_stacks( void );
void free_runtime_stacks( void );

/* ------------------------------------------------------------- */
/* Inc or dec comp_stack */
void inc_rt_comp_ptr( void );
void dec_rt_comp_ptr( void );

/* ------------------------------------------------------------- */
/* Inc or dec address_ptr */
void inc_rt_address_ptr( void );
void dec_rt_address_ptr( void );