#include <stdlib.h>
#include <stdio.h>
#include <string.h>

/*
 * VLA_ALLOC_LIMIT - define upper limit for VLA allocations
 *
 * This should be derived from |getpagesize()| but we
 * can't do it directly here because |getpagesize()| is
 * a syscall and therefore causes too much per-allocation
 * overhead
 */
#define VLA_ALLOC_LIMIT (4096*8)

#if (__STDC_VERSION__ - 0 >= 199901L) /* C99 */ && \
    (__STDC_NO_VLA__  - 0 <  1L)      /* C11 feature test for VLA support */

/*
 * VLA_ALLOC_ALLOCATE - allocate a chunk of memory from stack
 * if the size is smaller than |VLA_ALLOC_LIMIT| (and use
 * |malloc()| otherwise) and store the pointer to that memory
 * into |dest|
 *
 * Notes:
 * - We still use |1| as size for the VLA array if we use the
 * |malloc()| codepath because the ISO C1X standard is a bit
 * unclear in this corner case and (Sun Studio) lint(1) complains
 * about zero-sized VLA arrays
 * - We do not provide a codepath for |alloca()| as fallback
 * because there are platforms which define |alloca()| via a
 * wrapper around |malloc()| and therefore do not provide any
 * performance benefits
 */
#define VLA_ALLOC_ALLOCATE(dest, name, size) \
	const size_t mem_mallocsize##name = (size); \
        void *mem_malloc##name; \
	char *mem_vla##name[mem_mallocsize##name > VLA_ALLOC_LIMIT?1:(mem_mallocsize##name)]; \
        (((mem_mallocsize##name) > VLA_ALLOC_LIMIT)? \
                ((dest) = mem_malloc##name = malloc(mem_mallocsize##name)): \
                (mem_malloc##name = NULL, (dest) = mem_vla##name))
#else
#define VLA_ALLOC_ALLOCATE(dest, name, size) \
        void *mem_malloc##name; \
        ((dest) = mem_malloc##name = malloc(size))
#endif

/*
 * Free memory allocated via |VLA_ALLOC_ALLOCATE()|
 * POSIX |free()| handles NULL-pointers automagically
 */
#define VLA_ALLOC_FREE(name) free(mem_malloc##name)


int main(int ac, char *av[])
{
        void	*frog_mem,
		*fish_mem;
        size_t	i;
        
        for (i=0 ; i < ((VLA_ALLOC_LIMIT*5L)/4L) ; i++)
        {
                VLA_ALLOC_ALLOCATE(frog_mem, frog, i);
		if (frog_mem)
		{
			(void)strncpy(frog_mem, 
				"use memory to store frog data",
				i);
		}

                VLA_ALLOC_ALLOCATE(fish_mem, fish, i*2);
		if (frog_mem)
		{
			(void)strncpy(fish_mem,
				"use memory to store fish data",
				i*2);
		}

                VLA_ALLOC_FREE(frog);
                VLA_ALLOC_FREE(fish);
        }

        return (EXIT_SUCCESS);
}