/*
 * Copyright (c) 2016 Simon Schmidt
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include <stdint.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>
#include <string.h>

#ifndef MAP_ANONYMOUS
#define MAP_ANONYMOUS MAP_ANON
#endif

#define MPT MAP_PRIVATE|MAP_ANONYMOUS

#define PRT PROT_WRITE|PROT_READ

typedef union Premap_s {
	uintptr_t align;
	size_t allocsize;
} Premap;

static size_t rndup(size_t size){
	int pgs = getpagesize()-1;
	size+=sizeof(Premap);
	size+=pgs;
	size&=~pgs;
	return size;
}

void *malloc(size_t size){
	if(!size)return NULL;
	size=rndup(size);
	Premap* map = mmap(NULL,size,PRT,MPT,-1,0);
	if(map==MAP_FAILED)return NULL;
	map->allocsize=size;
	return &map[1];
}
void free(void *ptr){
	if(!ptr)return;
	Premap* map = (ptr-sizeof(Premap));
	size_t size = map->allocsize;
	munmap(map,size);
}
void *calloc(size_t nmemb, size_t size){
	size*=nmemb;
	return malloc(size);
}
void *realloc(void *ptr, size_t size){
	size_t oldsz,rsize;
	Premap *map,*nmap;
	void* nptr;

	if(!size){
		free(ptr);
		return NULL;
	}
	if(!ptr)return malloc(size);
	rsize=rndup(size);
	map = (ptr-sizeof(Premap));
	oldsz=map->allocsize;
	if(oldsz<rsize){ /* Growing the area */
		nmap = mmap(NULL,rsize,PRT,MPT,-1,0);
		if(nmap==MAP_FAILED) return NULL;
		memcpy(nmap,map,oldsz);
		nmap->allocsize = rsize;
		free(ptr);
		return &nmap[1];
	}else if(oldsz>rsize){ /* Shrinking the area */
		nmap = mmap(NULL,rsize,PRT,MPT,-1,0);
		if(nmap==MAP_FAILED) return ptr;
		memcpy(nmap,map,rsize);
		nmap->allocsize = rsize;
		free(ptr);
		return &nmap[1];
	}
	return ptr;
}