/*
 */

#include <stdlib.h>   /* malloc()/free() prototypes */
#include <string.h>   /* mem*() */
#include <sys/mman.h> /* mmap() */

#define SB_MALLOC_TO_MMAP(ptr) ((void*)(((size_t*)ptr) - 1))
#define SB_MMAP_TO_MALLOC(ptr) ((void*)(((size_t*)ptr) + 1))
#define SB_MALLOC_TO_SIZE(ptr) (*((size_t*)SB_MALLOC_TO_MMAP(ptr)))

void *malloc(size_t size)
{
	size_t *ret;
	size += sizeof(size_t);
	ret = mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
	if (ret == MAP_FAILED)
		return NULL;
	*ret = size;
	return SB_MMAP_TO_MALLOC(ret);
}

void free(void *ptr)
{
	if (ptr == NULL)
		return;
	munmap(SB_MALLOC_TO_MMAP(ptr), SB_MALLOC_TO_SIZE(ptr));
}

void *calloc(size_t nmemb, size_t size)
{
	void *ret;
	size_t malloc_size = nmemb * size;
	ret = malloc(malloc_size); /* dont care about overflow */
	memset(ret, 0x00, malloc_size);
	return ret;
}

void *realloc(void *ptr, size_t size)
{
	void *ret;
	size_t old_malloc_size;

	if (ptr == NULL)
		return malloc(size);
	if (size == 0) {
		free(ptr);
		return ptr;
	}

	old_malloc_size = SB_MALLOC_TO_SIZE(ptr);
	ret = malloc(size);
	memcpy(ret, ptr, old_malloc_size);
	free(ptr);
	return ret;
}