336 lines
8.9 KiB
Go
336 lines
8.9 KiB
Go
// Copyright 2011 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 misspell
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import (
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"io"
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// "log"
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"strings"
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)
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// StringReplacer replaces a list of strings with replacements.
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// It is safe for concurrent use by multiple goroutines.
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type StringReplacer struct {
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r replacer
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}
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// replacer is the interface that a replacement algorithm needs to implement.
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type replacer interface {
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Replace(s string) string
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WriteString(w io.Writer, s string) (n int, err error)
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}
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// NewStringReplacer returns a new Replacer from a list of old, new string pairs.
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// Replacements are performed in order, without overlapping matches.
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func NewStringReplacer(oldnew ...string) *StringReplacer {
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if len(oldnew)%2 == 1 {
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panic("strings.NewReplacer: odd argument count")
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}
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return &StringReplacer{r: makeGenericReplacer(oldnew)}
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}
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// Replace returns a copy of s with all replacements performed.
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func (r *StringReplacer) Replace(s string) string {
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return r.r.Replace(s)
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}
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// WriteString writes s to w with all replacements performed.
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func (r *StringReplacer) WriteString(w io.Writer, s string) (n int, err error) {
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return r.r.WriteString(w, s)
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}
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// trieNode is a node in a lookup trie for prioritized key/value pairs. Keys
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// and values may be empty. For example, the trie containing keys "ax", "ay",
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// "bcbc", "x" and "xy" could have eight nodes:
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//
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// n0 -
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// n1 a-
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// n2 .x+
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// n3 .y+
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// n4 b-
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// n5 .cbc+
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// n6 x+
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// n7 .y+
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//
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// n0 is the root node, and its children are n1, n4 and n6; n1's children are
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// n2 and n3; n4's child is n5; n6's child is n7. Nodes n0, n1 and n4 (marked
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// with a trailing "-") are partial keys, and nodes n2, n3, n5, n6 and n7
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// (marked with a trailing "+") are complete keys.
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type trieNode struct {
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// value is the value of the trie node's key/value pair. It is empty if
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// this node is not a complete key.
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value string
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// priority is the priority (higher is more important) of the trie node's
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// key/value pair; keys are not necessarily matched shortest- or longest-
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// first. Priority is positive if this node is a complete key, and zero
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// otherwise. In the example above, positive/zero priorities are marked
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// with a trailing "+" or "-".
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priority int
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// A trie node may have zero, one or more child nodes:
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// * if the remaining fields are zero, there are no children.
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// * if prefix and next are non-zero, there is one child in next.
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// * if table is non-zero, it defines all the children.
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//
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// Prefixes are preferred over tables when there is one child, but the
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// root node always uses a table for lookup efficiency.
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// prefix is the difference in keys between this trie node and the next.
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// In the example above, node n4 has prefix "cbc" and n4's next node is n5.
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// Node n5 has no children and so has zero prefix, next and table fields.
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prefix string
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next *trieNode
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// table is a lookup table indexed by the next byte in the key, after
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// remapping that byte through genericReplacer.mapping to create a dense
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// index. In the example above, the keys only use 'a', 'b', 'c', 'x' and
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// 'y', which remap to 0, 1, 2, 3 and 4. All other bytes remap to 5, and
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// genericReplacer.tableSize will be 5. Node n0's table will be
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// []*trieNode{ 0:n1, 1:n4, 3:n6 }, where the 0, 1 and 3 are the remapped
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// 'a', 'b' and 'x'.
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table []*trieNode
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}
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func (t *trieNode) add(key, val string, priority int, r *genericReplacer) {
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if key == "" {
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if t.priority == 0 {
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t.value = val
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t.priority = priority
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}
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return
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}
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if t.prefix != "" {
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// Need to split the prefix among multiple nodes.
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var n int // length of the longest common prefix
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for ; n < len(t.prefix) && n < len(key); n++ {
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if t.prefix[n] != key[n] {
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break
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}
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}
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if n == len(t.prefix) {
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t.next.add(key[n:], val, priority, r)
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} else if n == 0 {
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// First byte differs, start a new lookup table here. Looking up
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// what is currently t.prefix[0] will lead to prefixNode, and
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// looking up key[0] will lead to keyNode.
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var prefixNode *trieNode
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if len(t.prefix) == 1 {
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prefixNode = t.next
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} else {
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prefixNode = &trieNode{
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prefix: t.prefix[1:],
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next: t.next,
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}
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}
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keyNode := new(trieNode)
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t.table = make([]*trieNode, r.tableSize)
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t.table[r.mapping[t.prefix[0]]] = prefixNode
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t.table[r.mapping[key[0]]] = keyNode
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t.prefix = ""
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t.next = nil
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keyNode.add(key[1:], val, priority, r)
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} else {
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// Insert new node after the common section of the prefix.
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next := &trieNode{
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prefix: t.prefix[n:],
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next: t.next,
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}
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t.prefix = t.prefix[:n]
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t.next = next
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next.add(key[n:], val, priority, r)
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}
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} else if t.table != nil {
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// Insert into existing table.
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m := r.mapping[key[0]]
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if t.table[m] == nil {
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t.table[m] = new(trieNode)
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}
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t.table[m].add(key[1:], val, priority, r)
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} else {
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t.prefix = key
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t.next = new(trieNode)
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t.next.add("", val, priority, r)
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}
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}
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func (r *genericReplacer) lookup(s string, ignoreRoot bool) (val string, keylen int, found bool) {
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// Iterate down the trie to the end, and grab the value and keylen with
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// the highest priority.
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bestPriority := 0
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node := &r.root
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n := 0
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for node != nil {
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if node.priority > bestPriority && !(ignoreRoot && node == &r.root) {
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bestPriority = node.priority
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val = node.value
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keylen = n
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found = true
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}
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if s == "" {
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break
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}
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if node.table != nil {
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index := r.mapping[ByteToLower(s[0])]
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if int(index) == r.tableSize {
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break
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}
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node = node.table[index]
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s = s[1:]
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n++
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} else if node.prefix != "" && StringHasPrefixFold(s, node.prefix) {
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n += len(node.prefix)
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s = s[len(node.prefix):]
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node = node.next
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} else {
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break
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}
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}
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return
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}
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// genericReplacer is the fully generic algorithm.
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// It's used as a fallback when nothing faster can be used.
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type genericReplacer struct {
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root trieNode
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// tableSize is the size of a trie node's lookup table. It is the number
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// of unique key bytes.
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tableSize int
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// mapping maps from key bytes to a dense index for trieNode.table.
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mapping [256]byte
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}
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func makeGenericReplacer(oldnew []string) *genericReplacer {
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r := new(genericReplacer)
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// Find each byte used, then assign them each an index.
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for i := 0; i < len(oldnew); i += 2 {
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key := strings.ToLower(oldnew[i])
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for j := 0; j < len(key); j++ {
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r.mapping[key[j]] = 1
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}
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}
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for _, b := range r.mapping {
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r.tableSize += int(b)
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}
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var index byte
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for i, b := range r.mapping {
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if b == 0 {
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r.mapping[i] = byte(r.tableSize)
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} else {
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r.mapping[i] = index
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index++
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}
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}
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// Ensure root node uses a lookup table (for performance).
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r.root.table = make([]*trieNode, r.tableSize)
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for i := 0; i < len(oldnew); i += 2 {
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r.root.add(strings.ToLower(oldnew[i]), oldnew[i+1], len(oldnew)-i, r)
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}
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return r
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}
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type appendSliceWriter []byte
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// Write writes to the buffer to satisfy io.Writer.
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func (w *appendSliceWriter) Write(p []byte) (int, error) {
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*w = append(*w, p...)
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return len(p), nil
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}
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// WriteString writes to the buffer without string->[]byte->string allocations.
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func (w *appendSliceWriter) WriteString(s string) (int, error) {
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*w = append(*w, s...)
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return len(s), nil
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}
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type stringWriterIface interface {
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WriteString(string) (int, error)
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}
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type stringWriter struct {
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w io.Writer
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}
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func (w stringWriter) WriteString(s string) (int, error) {
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return w.w.Write([]byte(s))
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}
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func getStringWriter(w io.Writer) stringWriterIface {
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sw, ok := w.(stringWriterIface)
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if !ok {
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sw = stringWriter{w}
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}
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return sw
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}
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func (r *genericReplacer) Replace(s string) string {
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buf := make(appendSliceWriter, 0, len(s))
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r.WriteString(&buf, s)
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return string(buf)
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}
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func (r *genericReplacer) WriteString(w io.Writer, s string) (n int, err error) {
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sw := getStringWriter(w)
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var last, wn int
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var prevMatchEmpty bool
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for i := 0; i <= len(s); {
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// Fast path: s[i] is not a prefix of any pattern.
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if i != len(s) && r.root.priority == 0 {
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index := int(r.mapping[ByteToLower(s[i])])
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if index == r.tableSize || r.root.table[index] == nil {
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i++
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continue
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}
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}
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// Ignore the empty match iff the previous loop found the empty match.
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val, keylen, match := r.lookup(s[i:], prevMatchEmpty)
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prevMatchEmpty = match && keylen == 0
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if match {
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orig := s[i : i+keylen]
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switch CaseStyle(orig) {
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case CaseUnknown:
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// pretend we didn't match
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// i++
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// continue
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case CaseUpper:
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val = strings.ToUpper(val)
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case CaseLower:
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val = strings.ToLower(val)
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case CaseTitle:
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if len(val) < 2 {
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val = strings.ToUpper(val)
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} else {
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val = strings.ToUpper(val[:1]) + strings.ToLower(val[1:])
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}
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}
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wn, err = sw.WriteString(s[last:i])
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n += wn
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if err != nil {
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return
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}
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//log.Printf("%d: Going to correct %q with %q", i, s[i:i+keylen], val)
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wn, err = sw.WriteString(val)
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n += wn
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if err != nil {
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return
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}
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i += keylen
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last = i
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continue
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}
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i++
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}
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if last != len(s) {
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wn, err = sw.WriteString(s[last:])
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n += wn
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}
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return
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}
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