4ed7e529db
There are instantiations of binary_search() used in sstables.cc, but defined in partition.cc. The instantiations are explicitly declared in partition.cc, but the types changed and they became obsolete. The thing worked because partition.cc also instantiated it with the right type. But after that code will be removed, it no longer would, and we would get a linker error. To avoid such problems, define binary_search() in a header.
90 lines
3.0 KiB
C++
90 lines
3.0 KiB
C++
/*
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* Copyright (C) 2017 ScyllaDB
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*
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include "sstables/key.hh"
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#include "dht/i_partitioner.hh"
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namespace sstables {
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/**
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* @returns: >= 0, if key is found. That is the index where the key is found.
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* -1, if key is not found, and is smaller than the first key in the list.
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* <= -2, if key is not found, but is greater than one of the keys. By adding 2 and
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* negating, one can determine the index before which the key would have to
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* be inserted.
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*
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* Origin uses this slightly modified binary search for the Summary, that will
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* indicate in which bucket the element would be in case it is not a match.
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*
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* For the Index entries, it uses a "normal", java.lang binary search. Because
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* we have made the explicit decision to open code the comparator for
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* efficiency, using a separate binary search would be possible, but very
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* messy.
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*
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* It's easier to reuse the same code for both binary searches, and just ignore
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* the extra information when not needed.
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*
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* This code should work in all kinds of vectors in whose's elements is possible to aquire
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* a key view via get_key().
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*/
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template <typename T>
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int binary_search(const T& entries, const key& sk, const dht::token& token) {
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int low = 0, mid = entries.size(), high = mid - 1, result = -1;
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auto& partitioner = dht::global_partitioner();
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while (low <= high) {
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// The token comparison should yield the right result most of the time.
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// So we avoid expensive copying operations that happens at key
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// creation by keeping only a key view, and then manually carrying out
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// both parts of the comparison ourselves.
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mid = low + ((high - low) >> 1);
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key_view mid_key = entries[mid].get_key();
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auto mid_token = partitioner.get_token(mid_key);
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if (token == mid_token) {
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result = sk.tri_compare(mid_key);
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} else {
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result = token < mid_token ? -1 : 1;
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}
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if (result > 0) {
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low = mid + 1;
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} else if (result < 0) {
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high = mid - 1;
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} else {
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return mid;
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}
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}
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return -mid - (result < 0 ? 1 : 2);
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}
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template <typename T>
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int binary_search(const T& entries, const key& sk) {
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return binary_search(entries, sk, dht::global_partitioner().get_token(key_view(sk)));
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}
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}
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