ptrtag.h

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/*
 * Copyright (C) 2020 Otto-von-Guericke-Universität Magdeburg
 *
 * This file is subject to the terms and conditions of the GNU Lesser General
 * Public License v2.1. See the file LICENSE in the top level directory for more
 * details.
 */
 
#pragma once
 
#include <assert.h>
#include <inttypes.h>
#include <stdint.h>
 
#ifdef __cplusplus
extern "C" {
#endif
 
#define PTRTAG  __attribute__((aligned(4)))
 
static inline void * ptrtag(void *ptr, uint8_t tag)
{
    uintptr_t tmp = (uintptr_t)ptr;
    /* ensure ptr is aligned to four bytes and tag fits in two bits */
    assert((tag < 4) && !(tmp & 0x3));
    return (void *)(tmp | tag);
}
 
static inline void * ptrtag_ptr(void *tagged_ptr)
{
    uintptr_t tagged = (uintptr_t)tagged_ptr;
    const uintptr_t mask = 0x3;
    return (void *)(tagged & (~mask));
}
 
static inline uint8_t ptrtag_tag(void *tagged_ptr)
{
    uintptr_t tagged = (uintptr_t)tagged_ptr;
    return tagged & 0x3;
}
 
#ifdef __cplusplus
}
#endif