Don Newton | 379ae25 | 2019-04-01 12:17:06 -0400 | [diff] [blame^] | 1 | // Copyright 2014 The Go Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | package triegen |
| 6 | |
| 7 | // This file defines Compacter and its implementations. |
| 8 | |
| 9 | import "io" |
| 10 | |
| 11 | // A Compacter generates an alternative, more space-efficient way to store a |
| 12 | // trie value block. A trie value block holds all possible values for the last |
| 13 | // byte of a UTF-8 encoded rune. Excluding ASCII characters, a trie value block |
| 14 | // always has 64 values, as a UTF-8 encoding ends with a byte in [0x80, 0xC0). |
| 15 | type Compacter interface { |
| 16 | // Size returns whether the Compacter could encode the given block as well |
| 17 | // as its size in case it can. len(v) is always 64. |
| 18 | Size(v []uint64) (sz int, ok bool) |
| 19 | |
| 20 | // Store stores the block using the Compacter's compression method. |
| 21 | // It returns a handle with which the block can be retrieved. |
| 22 | // len(v) is always 64. |
| 23 | Store(v []uint64) uint32 |
| 24 | |
| 25 | // Print writes the data structures associated to the given store to w. |
| 26 | Print(w io.Writer) error |
| 27 | |
| 28 | // Handler returns the name of a function that gets called during trie |
| 29 | // lookup for blocks generated by the Compacter. The function should be of |
| 30 | // the form func (n uint32, b byte) uint64, where n is the index returned by |
| 31 | // the Compacter's Store method and b is the last byte of the UTF-8 |
| 32 | // encoding, where 0x80 <= b < 0xC0, for which to do the lookup in the |
| 33 | // block. |
| 34 | Handler() string |
| 35 | } |
| 36 | |
| 37 | // simpleCompacter is the default Compacter used by builder. It implements a |
| 38 | // normal trie block. |
| 39 | type simpleCompacter builder |
| 40 | |
| 41 | func (b *simpleCompacter) Size([]uint64) (sz int, ok bool) { |
| 42 | return blockSize * b.ValueSize, true |
| 43 | } |
| 44 | |
| 45 | func (b *simpleCompacter) Store(v []uint64) uint32 { |
| 46 | h := uint32(len(b.ValueBlocks) - blockOffset) |
| 47 | b.ValueBlocks = append(b.ValueBlocks, v) |
| 48 | return h |
| 49 | } |
| 50 | |
| 51 | func (b *simpleCompacter) Print(io.Writer) error { |
| 52 | // Structures are printed in print.go. |
| 53 | return nil |
| 54 | } |
| 55 | |
| 56 | func (b *simpleCompacter) Handler() string { |
| 57 | panic("Handler should be special-cased for this Compacter") |
| 58 | } |