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construct/include/ircd/db/comparator.h

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// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 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
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// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.
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#pragma once
#define HAVE_IRCD_DB_COMPARATOR_H
namespace ircd::db
{
struct comparator;
template<class T> struct cmp_integer;
template<class T> struct reverse_cmp_integer;
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struct cmp_int64_t;
struct reverse_cmp_int64_t;
struct cmp_uint64_t;
struct reverse_cmp_uint64_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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{}
};
template<class T>
struct ircd::db::cmp_integer
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:db::comparator
{
static bool less(const string_view &sa, const string_view &sb)
{
const byte_view<T> a{sa}, b{sb};
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return a < b;
}
static bool equal(const string_view &sa, const string_view &sb)
{
const byte_view<T> a{sa}, b{sb};
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return a == b;
}
cmp_integer()
:db::comparator{"integer", &less, &equal}
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{}
};
template<class T>
struct ircd::db::reverse_cmp_integer
:db::comparator
{
static bool less(const string_view &sa, const string_view &sb)
{
const byte_view<T> a{sa}, b{sb};
return a > b;
}
static bool equal(const string_view &sa, const string_view &sb)
{
return cmp_integer<T>::equal(sa, sb);
}
reverse_cmp_integer()
:db::comparator{"reverse_integer", &less, &equal}
{}
};
struct ircd::db::cmp_int64_t
:cmp_integer<int64_t>
{
using cmp_integer<int64_t>::cmp_integer;
};
struct ircd::db::reverse_cmp_int64_t
:reverse_cmp_integer<int64_t>
{
using reverse_cmp_integer<int64_t>::reverse_cmp_integer;
};
struct ircd::db::cmp_uint64_t
:cmp_integer<uint64_t>
{
using cmp_integer<uint64_t>::cmp_integer;
};
struct ircd::db::reverse_cmp_uint64_t
:reverse_cmp_integer<uint64_t>
{
using reverse_cmp_integer<uint64_t>::reverse_cmp_integer;
};