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58 lines
2 KiB
Go
58 lines
2 KiB
Go
// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package triegen
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// This file defines Compacter and its implementations.
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import "io"
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// A Compacter generates an alternative, more space-efficient way to store a
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// trie value block. A trie value block holds all possible values for the last
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// byte of a UTF-8 encoded rune. Excluding ASCII characters, a trie value block
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// always has 64 values, as a UTF-8 encoding ends with a byte in [0x80, 0xC0).
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type Compacter interface {
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// Size returns whether the Compacter could encode the given block as well
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// as its size in case it can. len(v) is always 64.
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Size(v []uint64) (sz int, ok bool)
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// Store stores the block using the Compacter's compression method.
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// It returns a handle with which the block can be retrieved.
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// len(v) is always 64.
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Store(v []uint64) uint32
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// Print writes the data structures associated to the given store to w.
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Print(w io.Writer) error
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// Handler returns the name of a function that gets called during trie
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// lookup for blocks generated by the Compacter. The function should be of
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// the form func (n uint32, b byte) uint64, where n is the index returned by
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// the Compacter's Store method and b is the last byte of the UTF-8
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// encoding, where 0x80 <= b < 0xC0, for which to do the lookup in the
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// block.
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Handler() string
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}
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// simpleCompacter is the default Compacter used by builder. It implements a
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// normal trie block.
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type simpleCompacter builder
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func (b *simpleCompacter) Size([]uint64) (sz int, ok bool) {
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return blockSize * b.ValueSize, true
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}
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func (b *simpleCompacter) Store(v []uint64) uint32 {
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h := uint32(len(b.ValueBlocks) - blockOffset)
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b.ValueBlocks = append(b.ValueBlocks, v)
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return h
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}
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func (b *simpleCompacter) Print(io.Writer) error {
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// Structures are printed in print.go.
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return nil
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}
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func (b *simpleCompacter) Handler() string {
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panic("Handler should be special-cased for this Compacter")
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}
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