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// Copyright 2020-2021 the Blobloom authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// This package implements a toy interactive spell checker.
//
// It reads a dictionary from /usr/share/dict/words and a text from standard
// input. It then reports any misspelled words on standard output.
package main
import (
"bufio"
"bytes"
"fmt"
"hash/maphash"
"log"
"os"
"unicode"
"github.com/greatroar/blobloom"
)
func main() {
dict := loadDictionary()
sc := bufio.NewScanner(os.Stdin)
sc.Split(bufio.ScanWords)
for sc.Scan() {
word := normalize(sc.Bytes())
if !dict.has(word) {
fmt.Printf(">>> %s\n", word)
}
}
if err := sc.Err(); err != nil {
log.Fatal(err)
}
}
// A Bloom filter with a randomized hash function.
type bloomfilter struct {
*blobloom.Filter
maphash.Seed
}
func newBloomfilter(capacity uint64, fprate float64) *bloomfilter {
cfg := blobloom.Config{Capacity: capacity, FPRate: .001}
return &bloomfilter{
Filter: blobloom.NewOptimized(cfg),
Seed: maphash.MakeSeed(),
}
}
func (f *bloomfilter) add(key []byte) { f.Filter.Add(f.hash(key)) }
func (f *bloomfilter) has(key []byte) bool { return f.Filter.Has(f.hash(key)) }
func (f *bloomfilter) hash(key []byte) uint64 {
var h maphash.Hash
h.SetSeed(f.Seed)
_, _ = h.Write(key)
return h.Sum64()
}
func normalize(word []byte) []byte {
word = bytes.TrimFunc(word, unicode.IsPunct)
word = bytes.ToLower(word)
return word
}
// To estimate the number of keys without scanning the file twice, we need
// an estimate of the average length of a word. This comes close for English.
const avgWordLength = 10
func loadDictionary() *bloomfilter {
f, err := os.Open("/usr/share/dict/words")
if err != nil {
log.Fatal(err)
}
defer f.Close()
info, err := f.Stat()
if err != nil {
log.Fatal(err)
}
filesize := uint64(info.Size())
dict := newBloomfilter(filesize/avgWordLength, .001)
sc := bufio.NewScanner(f)
for sc.Scan() {
dict.add(normalize(sc.Bytes()))
filesize-- // Subtract newline, for fairness.
}
if err := sc.Err(); err != nil {
log.Fatal(err)
}
log.Printf("dictionary loaded: %dkiB on disk, %dkiB in memory",
filesize/1024, dict.NumBits()/(8*1024))
return dict
}
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