layers/cast_utils.h

/* Copyright (c) 2019 The Khronos Group Inc.
 * Copyright (c) 2019 Valve Corporation
 * Copyright (c) 2019 LunarG, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Author: John Zulauf <jzulauf@lunarg.com>
 *
 */
#pragma once
#ifndef CAST_UTILS_H_
#define CAST_UTILS_H_

#include <cassert>
#include <cstddef>
#include <cstdint>
#include <functional>

#define CAST_TO_FROM_UTILS
// Casts to allow various types of less than 64 bits to be cast to and from uint64_t safely and portably
template <typename HandleType, typename Uint>
static inline HandleType CastFromUint(Uint untyped_handle) {
    static_assert(sizeof(HandleType) == sizeof(Uint), "HandleType must be the same size as untyped handle");
    return *reinterpret_cast<HandleType *>(&untyped_handle);
}
template <typename HandleType, typename Uint>
static inline Uint CastToUint(HandleType handle) {
    static_assert(sizeof(HandleType) == sizeof(Uint), "HandleType must be the same size as untyped handle");
    return *reinterpret_cast<Uint *>(&handle);
}

// Ensure that the size changing casts are *static* to ensure portability
template <typename HandleType>
static inline HandleType CastFromUint64(uint64_t untyped_handle) {
    static_assert(sizeof(HandleType) <= sizeof(uint64_t), "HandleType must be not larger than the untyped handle size");
    typedef
        typename std::conditional<sizeof(HandleType) == sizeof(uint8_t), uint8_t,
                                  typename std::conditional<sizeof(HandleType) == sizeof(uint16_t), uint16_t,
                                                            typename std::conditional<sizeof(HandleType) == sizeof(uint32_t),
                                                                                      uint32_t, uint64_t>::type>::type>::type Uint;
    return CastFromUint<HandleType, Uint>(static_cast<Uint>(untyped_handle));
}

template <typename HandleType>
static uint64_t CastToUint64(HandleType handle) {
    static_assert(sizeof(HandleType) <= sizeof(uint64_t), "HandleType must be not larger than the untyped handle size");
    typedef
        typename std::conditional<sizeof(HandleType) == sizeof(uint8_t), uint8_t,
                                  typename std::conditional<sizeof(HandleType) == sizeof(uint16_t), uint16_t,
                                                            typename std::conditional<sizeof(HandleType) == sizeof(uint32_t),
                                                                                      uint32_t, uint64_t>::type>::type>::type Uint;
    return static_cast<uint64_t>(CastToUint<HandleType, Uint>(handle));
}

// Convenience functions to case between handles and the types the handles abstract, reflecting the Vulkan handle scheme, where
// Handles are either pointers (dispatchable) or sizeof(uint64_t) (non-dispatchable), s.t. full size-safe casts are used and
// we ensure that handles are large enough to contain the underlying type.
template <typename HandleType, typename ValueType>
void CastToHandle(ValueType value, HandleType *handle) {
    static_assert(sizeof(HandleType) >= sizeof(ValueType), "HandleType must large enough to hold internal value");
    *handle = CastFromUint64<HandleType>(CastToUint64<ValueType>(value));
}
// This form is conveniently "inline", you should only need to specify the handle type (the value type being deducible from the arg)
template <typename HandleType, typename ValueType>
HandleType CastToHandle(ValueType value) {
    HandleType handle;
    CastToHandle(value, &handle);
    return handle;
}

template <typename ValueType, typename HandleType>
void CastFromHandle(HandleType handle, ValueType *value) {
    static_assert(sizeof(HandleType) >= sizeof(ValueType), "HandleType must large enough to hold internal value");
    *value = CastFromUint64<ValueType>(CastToUint64<HandleType>(handle));
}
template <typename ValueType, typename HandleType>
ValueType CastFromHandle(HandleType handle) {
    ValueType value;
    CastFromHandle(handle, &value);
    return value;
}

#endif  // CAST_UTILS_H_