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77 lines
2.3 KiB
Markdown
77 lines
2.3 KiB
Markdown
7 years ago
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# unicode-trie
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A data structure for fast Unicode character metadata lookup, ported from ICU
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## Background
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When implementing many Unicode algorithms such as text segmentation,
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normalization, bidi processing, etc., fast access to character metadata
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is crucial to good performance. There over a million code points in the
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Unicode standard, many of which produce the same result when looked up,
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so an array or hash table is not appropriate - those data structures are
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fast but would require a lot of memory. The data is generally
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grouped in ranges, so you could do a binary search, but that is not
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fast enough for some applications.
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The [International Components for Unicode](http://site.icu-project.org) (ICU) project
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came up with a data structure based on a [Trie](http://en.wikipedia.org/wiki/Trie) that provides fast access
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to Unicode metadata. The range data is precompiled to a serialized
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and flattened trie, which is then used at runtime to lookup the necessary
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data. According to my own tests, this is generally at least 50% faster
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than binary search, with not too much additional memory required.
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## Installation
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npm install unicode-trie
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## Building a Trie
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Unicode Tries are generally precompiled from data in the Unicode database
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for faster runtime performance. To build a Unicode Trie, use the
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`UnicodeTrieBuilder` class.
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```coffeescript
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UnicodeTrieBuilder = require 'unicode-trie/builder'
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# create a trie
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t = new UnicodeTrieBuilder
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# optional parameters for default value, and error value
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# if not provided, both are set to 0
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t = new UnicodeTrieBuilder 10, 999
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# set individual values and ranges
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t.set 0x4567, 99
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t.setRange 0x40, 0xe7, 0x1234
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# you can lookup a value if you like
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t.get 0x4567 # => 99
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# get a compiled trie (returns a UnicodeTrie object)
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trie = t.freeze()
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# write compressed trie to a binary file
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fs.writeFile 'data.trie', t.toBuffer()
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```
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## Using a precompiled Trie
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Once you've built a precompiled trie, you can load it into the
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`UnicodeTrie` class, which is a readonly representation of the
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trie. From there, you can lookup values.
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```coffeescript
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UnicodeTrie = require 'unicode-trie'
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fs = require 'fs'
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# load serialized trie from binary file
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data = fs.readFileSync 'data.trie'
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trie = new UnicodeTrie data
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# lookup a value
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trie.get 0x4567 # => 99
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```
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## License
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MIT
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