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114 lines
4.8 KiB
C++
114 lines
4.8 KiB
C++
/*
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* Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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#include <cstring>
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#include "utilities/align.hpp"
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#include "utilities/count_leading_zeros.hpp"
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#include "utilities/packedTable.hpp"
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// The thresholds are inclusive, and in practice the limits are rounded
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// to the nearest power-of-two - 1.
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// Based on the max_key and max_value we figure out the number of bits required to store
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// key and value; imagine that only as bits (not aligned to byte boundary... yet).
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// Then we concatenate the bits for key and value, and 'add' 1-7 padding zeroes
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// (high-order bits) to align on bytes.
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// In the end we have each element in the table consuming 1-8 bytes (case with 0 bits for key
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// is ruled out).
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PackedTableBase::PackedTableBase(uint32_t max_key, uint32_t max_value) {
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unsigned int key_bits = max_key == 0 ? 0 : 32 - count_leading_zeros(max_key);
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unsigned int value_bits = max_value == 0 ? 0 : 32 - count_leading_zeros(max_value);
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_element_bytes = align_up(key_bits + value_bits, 8) / 8;
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// shifting left by 32 is undefined behaviour, and in practice returns 1
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_key_mask = key_bits >= 32 ? -1 : (1U << key_bits) - 1;
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_value_shift = key_bits;
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_value_mask = value_bits >= 32 ? -1 : (1U << value_bits) - 1;
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guarantee(_element_bytes > 0, "wouldn't work");
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assert(_element_bytes <= sizeof(uint64_t), "shouldn't happen");
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}
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// Note: we require the supplier to provide the elements in the final order as we can't easily sort
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// within this method - qsort() accepts only pure function as comparator.
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void PackedTableBuilder::fill(u1* table, size_t table_length, Supplier &supplier) const {
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uint32_t key, value;
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size_t offset = 0;
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for (; offset <= table_length && supplier.next(&key, &value); offset += _element_bytes) {
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assert((key & ~_key_mask) == 0, "key out of bounds");
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assert((value & ~_value_mask) == 0, "value out of bounds: %x vs. %x (%x)", value, _value_mask, ~_value_mask);
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uint64_t element = static_cast<uint64_t>(key) | (static_cast<uint64_t>(value) << _value_shift);
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for (unsigned int i = 0; i < _element_bytes; ++i) {
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table[offset + i] = static_cast<u1>(0xFF & element);
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element >>= 8;
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}
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}
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assert(offset == table_length, "Did not fill whole array");
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assert(!supplier.next(&key, &value), "Supplier has more elements");
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}
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uint64_t PackedTableLookup::read_element(size_t offset) const {
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uint64_t element = 0;
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for (unsigned int i = 0; i < _element_bytes; ++i) {
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element |= static_cast<uint64_t>(_table[offset + i]) << (8 * i);
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}
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assert((element & ~((uint64_t) _key_mask | ((uint64_t) _value_mask << _value_shift))) == 0, "read too much");
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return element;
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}
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bool PackedTableLookup::search(Comparator& comparator, uint32_t* found_key, uint32_t* found_value) const {
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unsigned int low = 0, high = checked_cast<unsigned int>(_table_length / _element_bytes);
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assert(low < high, "must be");
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while (low < high) {
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unsigned int mid = low + (high - low) / 2;
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assert(mid >= low && mid < high, "integer overflow?");
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uint64_t element = read_element(_element_bytes * mid);
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// Ignoring high 32 bits in element on purpose
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uint32_t key = static_cast<uint32_t>(element) & _key_mask;
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int cmp = comparator.compare_to(key);
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if (cmp == 0) {
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*found_key = key;
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// Since __builtin_memcpy in read_element does not copy bits outside the element
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// anything above _value_mask << _value_shift should be zero.
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*found_value = checked_cast<uint32_t>(element >> _value_shift) & _value_mask;
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return true;
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} else if (cmp < 0) {
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high = mid;
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} else {
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low = mid + 1;
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}
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}
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return false;
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}
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#ifdef ASSERT
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void PackedTableLookup::validate_order(Comparator &comparator) const {
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auto validator = [&] (size_t offset, uint32_t key, uint32_t value) {
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if (offset != 0) {
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assert(comparator.compare_to(key) < 0, "not sorted");
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}
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comparator.reset(key);
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};
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iterate(validator);
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}
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#endif
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