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