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/***************************************************************************************************
* Copyright (c) 2023 - 2024 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
* SPDX-License-Identifier: BSD-3-Clause
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* 3. Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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*
**************************************************************************************************/
/*! \file
\brief Portable bit field that supports byte and word straddling that can
be used in unions to bit-wise define parameters.
*/
#pragma once
#include <cute/config.hpp>
#include <cute/numeric/numeric_types.hpp> // uint_bit_t
namespace cute
{
class dummy_type {};
template <uint32_t BitStart, uint32_t NumBits, class OtherValueType = dummy_type>
struct bit_field
{
static_assert(0 < NumBits && NumBits <= 64, "bit_fields with more than 64 bits are not supported.");
// value_type: Use the smallest value type that fits NumBits
static constexpr uint32_t value_type_bits = (NumBits <= 8) ? 8 :
(NumBits <= 16) ? 16 :
(NumBits <= 32) ? 32 : 64;
using value_type = cute::uint_bit_t<value_type_bits>;
// storage_type: Use the smallest storage_type that avoids boundary crossing
static constexpr uint32_t storage_type_bits = (BitStart / 8 == (BitStart + NumBits - 1) / 8) ? 8 :
(BitStart / 16 == (BitStart + NumBits - 1) / 16) ? 16 :
(BitStart / 32 == (BitStart + NumBits - 1) / 32) ? 32 : 64;
using storage_type = cute::uint_bit_t<storage_type_bits>;
static_assert(sizeof(OtherValueType) == sizeof(value_type) || is_same<OtherValueType,dummy_type>::value,
"sizeof(OtherValueType) must be same as sizeof(value_type).");
// Number of storage values needed: ceil_div(BitStart + NumBits, storage_type_bits)
static constexpr uint32_t N = (BitStart + NumBits + storage_type_bits - 1) / storage_type_bits;
// Index of storage value for BitStart
static constexpr uint32_t idx = BitStart / storage_type_bits;
// Bit of data_[idx] for BitStart
static constexpr uint32_t bit_lo = BitStart % storage_type_bits;
// Number of bits in data_[idx] used for NumBits if straddling, else 0
static constexpr uint32_t bit_hi = (idx + 1 < N) ? (storage_type_bits - bit_lo) : 0;
public:
// NumBits mask
static constexpr value_type mask = value_type(uint64_t(-1) >> (64u - NumBits));
// NumBits mask for BitStart
static constexpr storage_type mask_lo = storage_type(mask) << bit_lo;
// NumBits mask for leftover bits in data_[idx+1] if straddling, else 0
static constexpr storage_type mask_hi = (idx + 1 < N) ? (storage_type(mask) >> bit_hi) : 0;
storage_type data_[N];
// Get value
CUTE_HOST_DEVICE constexpr
value_type get() const {
storage_type result = (data_[idx] & mask_lo) >> bit_lo;
if constexpr (bit_hi != 0) {
result |= (data_[idx+1] & mask_hi) << bit_hi;
}
return static_cast<value_type>(result);
}
// Set value
CUTE_HOST_DEVICE constexpr
void set(value_type x) {
storage_type item = static_cast<storage_type>(x & mask);
data_[idx] = static_cast<storage_type>((data_[idx] & ~mask_lo) | (item << bit_lo));
if constexpr (bit_hi != 0) {
data_[idx+1] = static_cast<storage_type>((data_[idx+1] & ~mask_hi) | (item >> bit_hi));
}
}
// Assign value
CUTE_HOST_DEVICE constexpr
bit_field& operator=(value_type x) {
set(x);
return *this;
}
// Cast to value
CUTE_HOST_DEVICE constexpr
operator value_type () const {
return get();
}
// Assign OtherValueType
CUTE_HOST_DEVICE constexpr
bit_field& operator=(OtherValueType x) {
return *this = *reinterpret_cast<value_type*>(&x);
}
// Cast to OtherValueType
CUTE_HOST_DEVICE constexpr
operator OtherValueType () const {
value_type x = get();
return *reinterpret_cast<OtherValueType*>(&x);
}
};
} // end namespace cute
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