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58 lines
2.1 KiB
Go
58 lines
2.1 KiB
Go
// Copyright (c) 2012, Suryandaru Triandana <syndtr@gmail.com>
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// All rights reserved.
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//
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// Package comparer provides interface and implementation for ordering
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// sets of data.
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package comparer
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// BasicComparer is the interface that wraps the basic Compare method.
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type BasicComparer interface {
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// Compare returns -1, 0, or +1 depending on whether a is 'less than',
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// 'equal to' or 'greater than' b. The two arguments can only be 'equal'
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// if their contents are exactly equal. Furthermore, the empty slice
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// must be 'less than' any non-empty slice.
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Compare(a, b []byte) int
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}
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// Comparer defines a total ordering over the space of []byte keys: a 'less
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// than' relationship.
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type Comparer interface {
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BasicComparer
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// Name returns name of the comparer.
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//
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// The Level-DB on-disk format stores the comparer name, and opening a
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// database with a different comparer from the one it was created with
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// will result in an error.
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//
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// An implementation to a new name whenever the comparer implementation
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// changes in a way that will cause the relative ordering of any two keys
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// to change.
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//
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// Names starting with "leveldb." are reserved and should not be used
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// by any users of this package.
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Name() string
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// Bellow are advanced functions used used to reduce the space requirements
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// for internal data structures such as index blocks.
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// Separator appends a sequence of bytes x to dst such that a <= x && x < b,
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// where 'less than' is consistent with Compare. An implementation should
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// return nil if x equal to a.
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//
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// Either contents of a or b should not by any means modified. Doing so
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// may cause corruption on the internal state.
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Separator(dst, a, b []byte) []byte
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// Successor appends a sequence of bytes x to dst such that x >= b, where
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// 'less than' is consistent with Compare. An implementation should return
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// nil if x equal to b.
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//
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// Contents of b should not by any means modified. Doing so may cause
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// corruption on the internal state.
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Successor(dst, b []byte) []byte
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}
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