ptrtag.h

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/*
 * SPDX-FileCopyrightText: 2020 Otto-von-Guericke-Universität Magdeburg
 * SPDX-License-Identifier: LGPL-2.1-only
 */
 
#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