511 lines
12 KiB
C++
511 lines
12 KiB
C++
// This file Copyright © 2008-2023 Mnemosyne LLC.
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// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
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// or any future license endorsed by Mnemosyne LLC.
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// License text can be found in the licenses/ folder.
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#include <algorithm>
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#include <array>
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#include <climits> // SIZE_MAX
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#include <vector>
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#include "libtransmission/transmission.h"
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#include "libtransmission/bitfield.h"
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#include "libtransmission/tr-assert.h"
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#include "libtransmission/tr-popcount.h"
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// ---
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namespace
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{
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[[nodiscard]] constexpr size_t getBytesNeeded(size_t bit_count) noexcept
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{
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/* NB: If can guarantee bit_count <= SIZE_MAX - 8 then faster logic
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is ((bit_count + 7) >> 3). */
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return (bit_count >> 3) + ((bit_count & 7) != 0 ? 1 : 0);
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}
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/* Used only in cases where it can be guaranteed bit_count <= SIZE_MAX - 8 */
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[[nodiscard]] constexpr size_t getBytesNeededSafe(size_t bit_count) noexcept
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{
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return ((bit_count + 7) >> 3);
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}
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void setAllTrue(uint8_t* array, size_t bit_count)
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{
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uint8_t constexpr Val = 0xFF;
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/* Only ever called internally with in-use bit counts. Impossible
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for bitcount > SIZE_MAX - 8. */
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size_t const n = getBytesNeededSafe(bit_count);
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if (n > 0)
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{
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std::fill_n(array, n, Val);
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/* -bit_count & 7U. Since bitcount is unsigned do ~bitcount +
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1 to replace -bitcount as linters warn about negating
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unsigned types. Any compiler will optimize ~x + 1 to -x in
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the backend. */
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uint32_t const shift = ((~bit_count) + 1) & 7U;
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array[n - 1] = Val << shift;
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}
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}
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/* Switch to std::popcount if project upgrades to c++20 or newer */
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[[nodiscard]] uint32_t doPopcount(uint8_t flags) noexcept
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{
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/* If flags are ever expanded to use machine words instead of
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uint8_t popcnt64 is also available */
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return tr_popcnt<uint8_t>::count(flags);
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}
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[[nodiscard]] size_t rawCountFlags(uint8_t const* flags, size_t n) noexcept
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{
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auto ret = size_t{};
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for (auto const* const end = flags + n; flags != end; ++flags)
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{
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ret += doPopcount(*flags);
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}
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return ret;
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}
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} // namespace
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// ---
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size_t tr_bitfield::count_flags() const noexcept
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{
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return rawCountFlags(std::data(flags_), std::size(flags_));
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}
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size_t tr_bitfield::count_flags(size_t begin, size_t end) const noexcept
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{
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auto ret = size_t{};
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size_t const first_byte = begin >> 3U;
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size_t const last_byte = (end - 1) >> 3U;
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if (bit_count_ == 0)
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{
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return 0;
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}
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if (first_byte >= std::size(flags_))
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{
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return 0;
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}
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TR_ASSERT(begin < end);
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TR_ASSERT(!std::empty(flags_));
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if (first_byte == last_byte)
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{
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uint8_t val = flags_[first_byte];
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auto i = begin & 7U;
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val <<= i;
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i = (begin - end) & 7U;
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val >>= i;
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ret = doPopcount(val);
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}
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else
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{
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size_t const walk_end = std::min(std::size(flags_), last_byte);
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/* first byte */
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size_t const first_shift = begin & 7U;
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uint8_t val = flags_[first_byte];
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val <<= first_shift;
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/* No need to shift back val for correct popcount. */
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ret = doPopcount(val);
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/* middle bytes */
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/* Use 2x accumulators to help alleviate high latency of
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popcnt instruction on many architectures. */
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size_t tmp_accum = 0;
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for (size_t i = first_byte + 1; i < walk_end;)
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{
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tmp_accum += doPopcount(flags_[i]);
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i += 2;
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if (i > walk_end)
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{
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break;
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}
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ret += doPopcount(flags_[i - 1]);
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}
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ret += tmp_accum;
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/* last byte */
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if (last_byte < std::size(flags_))
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{
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/* -end & 7U. Since bitcount is unsigned do ~end + 1 to
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replace -end as linters warn about negating unsigned
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types. Any compiler will optimize ~x + 1 to -x in the
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backend. */
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uint32_t const last_shift = (~end + 1) & 7U;
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val = flags_[last_byte];
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val >>= last_shift;
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/* No need to shift back val for correct popcount. */
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ret += doPopcount(val);
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}
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}
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TR_ASSERT(ret <= (begin - end));
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return ret;
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}
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size_t tr_bitfield::count(size_t begin, size_t end) const
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{
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if (has_all())
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{
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return end - begin;
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}
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if (has_none())
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{
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return 0;
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}
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return count_flags(begin, end);
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}
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// ---
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bool tr_bitfield::is_valid() const
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{
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return std::empty(flags_) || true_count_ == count_flags();
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}
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std::vector<uint8_t> tr_bitfield::raw() const
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{
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/* Impossible for bit_count_ to exceed SIZE_MAX - 8 */
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auto const n = getBytesNeededSafe(bit_count_);
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if (!std::empty(flags_))
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{
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return flags_;
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}
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auto raw = std::vector<uint8_t>(n);
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if (has_all())
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{
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setAllTrue(std::data(raw), bit_count_);
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}
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return raw;
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}
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void tr_bitfield::ensure_bits_alloced(size_t n)
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{
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bool const has_all = this->has_all();
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/* Can't use getBytesNeededSafe as n can be > SIZE_MAX - 8. */
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size_t const bytes_needed = has_all ? getBytesNeeded(std::max(n, true_count_)) : getBytesNeeded(n);
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if (std::size(flags_) < bytes_needed)
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{
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flags_.resize(bytes_needed);
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if (has_all)
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{
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setAllTrue(std::data(flags_), true_count_);
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}
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}
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}
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bool tr_bitfield::ensure_nth_bit_alloced(size_t nth)
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{
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// count is zero-based, so we need to allocate nth+1 bits before setting the nth */
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if (nth == SIZE_MAX)
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{
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return false;
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}
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ensure_bits_alloced(nth + 1);
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return true;
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}
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void tr_bitfield::set_true_count(size_t n) noexcept
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{
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TR_ASSERT(bit_count_ == 0 || n <= bit_count_);
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true_count_ = n;
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have_all_hint_ = n == bit_count_;
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have_none_hint_ = n == 0;
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if (has_all() || has_none())
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{
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free_array();
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}
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TR_ASSERT(is_valid());
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}
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void tr_bitfield::increment_true_count(size_t inc) noexcept
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{
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TR_ASSERT(bit_count_ == 0 || inc <= bit_count_);
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TR_ASSERT(bit_count_ == 0 || true_count_ <= bit_count_ - inc);
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set_true_count(true_count_ + inc);
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}
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void tr_bitfield::decrement_true_count(size_t dec) noexcept
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{
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TR_ASSERT(bit_count_ == 0 || dec <= bit_count_);
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TR_ASSERT(bit_count_ == 0 || true_count_ >= dec);
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set_true_count(true_count_ - dec);
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}
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// ---
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tr_bitfield::tr_bitfield(size_t bit_count)
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: bit_count_{ bit_count }
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{
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TR_ASSERT(is_valid());
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}
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void tr_bitfield::set_has_none() noexcept
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{
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free_array();
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true_count_ = 0;
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have_all_hint_ = false;
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have_none_hint_ = true;
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TR_ASSERT(is_valid());
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}
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void tr_bitfield::set_has_all() noexcept
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{
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free_array();
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true_count_ = bit_count_;
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have_all_hint_ = true;
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have_none_hint_ = false;
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TR_ASSERT(is_valid());
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}
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void tr_bitfield::set_raw(uint8_t const* raw, size_t byte_count)
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{
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flags_.assign(raw, raw + byte_count);
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// ensure any excess bits at the end of the array are set to '0'.
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if (byte_count == getBytesNeededSafe(bit_count_))
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{
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auto const excess_bit_count = byte_count * 8 - bit_count_;
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TR_ASSERT(excess_bit_count <= 7);
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if (excess_bit_count != 0)
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{
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flags_.back() &= 0xff << excess_bit_count;
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}
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}
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rebuild_true_count();
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}
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void tr_bitfield::set_from_bools(bool const* flags, size_t n)
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{
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size_t true_count = 0;
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free_array();
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ensure_bits_alloced(n);
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for (size_t i = 0; i < n; ++i)
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{
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if (flags[i])
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{
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++true_count;
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flags_[i >> 3U] |= (0x80 >> (i & 7U));
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}
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}
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set_true_count(true_count);
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}
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void tr_bitfield::set(size_t nth, bool value)
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{
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if (test(nth) == value)
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{
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return;
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}
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if (!ensure_nth_bit_alloced(nth))
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{
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return;
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}
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/* Already tested that val != nth bit so just swap */
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auto& byte = flags_[nth >> 3U];
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#ifdef TR_ENABLE_ASSERTS
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auto const old_byte_pop = doPopcount(byte);
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#endif
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byte ^= 0x80 >> (nth & 7U);
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#ifdef TR_ENABLE_ASSERTS
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auto const new_byte_pop = doPopcount(byte);
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#endif
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if (value)
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{
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++true_count_;
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TR_ASSERT(old_byte_pop + 1 == new_byte_pop);
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}
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else
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{
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--true_count_;
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TR_ASSERT(new_byte_pop + 1 == old_byte_pop);
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}
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have_all_hint_ = true_count_ == bit_count_;
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have_none_hint_ = true_count_ == 0;
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}
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/* Sets bit range [begin, end) to 1 */
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void tr_bitfield::set_span(size_t begin, size_t end, bool value)
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{
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// bounds check
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end = std::min(end, bit_count_);
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if (end == 0 || begin >= end)
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{
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return;
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}
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// NB: count(begin, end) can be quite expensive. Might be worth it
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// to fuse the count and set loop
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size_t const old_count = count(begin, end);
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size_t const new_count = value ? (end - begin) : 0;
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// did anything change?
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if (old_count == new_count)
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{
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return;
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}
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--end;
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if (!ensure_nth_bit_alloced(end))
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{
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return;
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}
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auto walk = begin >> 3;
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auto const last_byte = end >> 3;
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unsigned char first_mask = 0xff >> (begin & 7U);
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unsigned char last_mask = 0xff << ((~end) & 7U);
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if (value)
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{
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if (walk == last_byte)
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{
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flags_[walk] |= first_mask & last_mask;
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}
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else
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{
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flags_[walk] |= first_mask;
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/* last_byte is expected to be hot in cache due to earlier
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count(begin, end) */
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flags_[last_byte] |= last_mask;
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if (++walk < last_byte)
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{
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std::fill_n(std::data(flags_) + walk, last_byte - walk, 0xff);
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}
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}
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increment_true_count(new_count - old_count);
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}
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else
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{
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first_mask = ~first_mask;
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last_mask = ~last_mask;
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if (walk == last_byte)
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{
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flags_[walk] &= first_mask | last_mask;
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}
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else
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{
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flags_[walk] &= first_mask;
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/* last_byte is expected to be hot in cache due to earlier
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count(begin, end) */
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flags_[last_byte] &= last_mask;
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if (++walk < last_byte)
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{
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std::fill_n(std::data(flags_) + walk, last_byte - walk, 0);
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}
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}
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decrement_true_count(old_count);
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}
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}
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tr_bitfield& tr_bitfield::operator|=(tr_bitfield const& that) noexcept
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{
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if (has_all() || that.has_none())
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{
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return *this;
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}
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if (that.has_all() || has_none())
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{
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*this = that;
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return *this;
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}
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flags_.resize(std::max(std::size(flags_), std::size(that.flags_)));
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for (size_t i = 0, n = std::size(that.flags_); i < n; ++i)
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{
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flags_[i] |= that.flags_[i];
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}
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rebuild_true_count();
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return *this;
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}
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tr_bitfield& tr_bitfield::operator&=(tr_bitfield const& that) noexcept
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{
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if (has_none() || that.has_all())
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{
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return *this;
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}
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if (that.has_none() || has_all())
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{
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*this = that;
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return *this;
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}
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flags_.resize(std::min(std::size(flags_), std::size(that.flags_)));
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for (size_t i = 0, n = std::size(flags_); i < n; ++i)
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{
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flags_[i] &= that.flags_[i];
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}
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rebuild_true_count();
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return *this;
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}
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bool tr_bitfield::intersects(tr_bitfield const& that) const noexcept
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{
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if (has_none() || that.has_none())
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{
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return false;
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}
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if (has_all() || that.has_all())
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{
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return true;
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}
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for (size_t i = 0, n = std::min(std::size(flags_), std::size(that.flags_)); i < n; ++i)
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{
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if ((flags_[i] & that.flags_[i]) != 0U)
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{
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return true;
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}
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}
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return false;
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}
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