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construct/include/ircd/db/comparator.h

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/*
* Copyright (C) 2016 Charybdis Development Team
* Copyright (C) 2016 Jason Volk <jason@zemos.net>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice is present in all copies.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
* IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
*/
#pragma once
#define HAVE_IRCD_DB_COMPARATOR_H
namespace ircd::db
{
struct comparator;
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struct cmp_int64_t;
struct reverse_cmp_int64_t;
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struct cmp_string_view;
struct reverse_cmp_string_view;
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}
struct ircd::db::comparator
{
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string_view name;
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std::function<bool (const string_view &, const string_view &)> less;
std::function<bool (const string_view &, const string_view &)> equal;
};
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struct ircd::db::cmp_string_view
:db::comparator
{
static bool less(const string_view &a, const string_view &b)
{
return a < b;
}
static bool equal(const string_view &a, const string_view &b)
{
return a == b;
}
cmp_string_view()
:db::comparator{"string_view", &less, &equal}
{}
};
struct ircd::db::reverse_cmp_string_view
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:db::comparator
{
static bool less(const string_view &a, const string_view &b)
{
/// RocksDB sez things will not work correctly unless a shorter string
/// result returns less than a longer string even if one intends some
/// reverse ordering
if(a.size() < b.size())
return true;
/// Furthermore, b.size() < a.size() returning false from this function
/// appears to not be correct. The reversal also has to also come in
/// the form of a bytewise forward iteration.
return std::memcmp(a.data(), b.data(), std::min(a.size(), b.size())) > 0;
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}
static bool equal(const string_view &a, const string_view &b)
{
return a == b;
}
reverse_cmp_string_view()
:db::comparator{"reverse_string_view", &less, &equal}
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{}
};
struct ircd::db::cmp_int64_t
:db::comparator
{
static bool less(const string_view &sa, const string_view &sb)
{
assert(sa.size() == sizeof(int64_t) && sb.size() == sizeof(int64_t));
const byte_view<int64_t> a{sa}, b{sb};
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return a < b;
}
static bool equal(const string_view &sa, const string_view &sb)
{
assert(sa.size() == sizeof(int64_t) && sb.size() == sizeof(int64_t));
const byte_view<int64_t> a{sa}, b{sb};
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return a == b;
}
cmp_int64_t()
:db::comparator{"int64_t", &less, &equal}
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{}
};
struct ircd::db::reverse_cmp_int64_t
:db::comparator
{
static bool less(const string_view &a, const string_view &b)
{
return !cmp_int64_t::less(a, b);
}
static bool equal(const string_view &a, const string_view &b)
{
return cmp_int64_t::equal(a, b);
}
reverse_cmp_int64_t()
:db::comparator{"reverse_int64_t", &less, &equal}
{}
};