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path: root/src/pkg/strings/replace.go
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-rw-r--r--src/pkg/strings/replace.go416
1 files changed, 326 insertions, 90 deletions
diff --git a/src/pkg/strings/replace.go b/src/pkg/strings/replace.go
index f53a96ee0..f63b1792c 100644
--- a/src/pkg/strings/replace.go
+++ b/src/pkg/strings/replace.go
@@ -33,47 +33,45 @@ func NewReplacer(oldnew ...string) *Replacer {
panic("strings.NewReplacer: odd argument count")
}
- // Possible implementations.
- var (
- bb byteReplacer
- bs byteStringReplacer
- gen genericReplacer
- )
-
- allOldBytes, allNewBytes := true, true
- for len(oldnew) > 0 {
- old, new := oldnew[0], oldnew[1]
- oldnew = oldnew[2:]
- if len(old) != 1 {
- allOldBytes = false
+ if len(oldnew) == 2 && len(oldnew[0]) > 1 {
+ return &Replacer{r: makeSingleStringReplacer(oldnew[0], oldnew[1])}
+ }
+
+ allNewBytes := true
+ for i := 0; i < len(oldnew); i += 2 {
+ if len(oldnew[i]) != 1 {
+ return &Replacer{r: makeGenericReplacer(oldnew)}
}
- if len(new) != 1 {
+ if len(oldnew[i+1]) != 1 {
allNewBytes = false
}
+ }
- // generic
- gen.p = append(gen.p, pair{old, new})
-
- // byte -> string
- if allOldBytes {
- bs.old.set(old[0])
- bs.new[old[0]] = []byte(new)
- }
-
- // byte -> byte
- if allOldBytes && allNewBytes {
- bb.old.set(old[0])
- bb.new[old[0]] = new[0]
+ if allNewBytes {
+ bb := &byteReplacer{}
+ for i := 0; i < len(oldnew); i += 2 {
+ o, n := oldnew[i][0], oldnew[i+1][0]
+ if bb.old[o>>5]&uint32(1<<(o&31)) != 0 {
+ // Later old->new maps do not override previous ones with the same old string.
+ continue
+ }
+ bb.old.set(o)
+ bb.new[o] = n
}
+ return &Replacer{r: bb}
}
- if allOldBytes && allNewBytes {
- return &Replacer{r: &bb}
- }
- if allOldBytes {
- return &Replacer{r: &bs}
+ bs := &byteStringReplacer{}
+ for i := 0; i < len(oldnew); i += 2 {
+ o, new := oldnew[i][0], oldnew[i+1]
+ if bs.old[o>>5]&uint32(1<<(o&31)) != 0 {
+ // Later old->new maps do not override previous ones with the same old string.
+ continue
+ }
+ bs.old.set(o)
+ bs.new[o] = []byte(new)
}
- return &Replacer{r: &gen}
+ return &Replacer{r: bs}
}
// Replace returns a copy of s with all replacements performed.
@@ -86,79 +84,326 @@ func (r *Replacer) WriteString(w io.Writer, s string) (n int, err error) {
return r.r.WriteString(w, s)
}
-// genericReplacer is the fully generic (and least optimized) algorithm.
+// trieNode is a node in a lookup trie for prioritized key/value pairs. Keys
+// and values may be empty. For example, the trie containing keys "ax", "ay",
+// "bcbc", "x" and "xy" could have eight nodes:
+//
+// n0 -
+// n1 a-
+// n2 .x+
+// n3 .y+
+// n4 b-
+// n5 .cbc+
+// n6 x+
+// n7 .y+
+//
+// n0 is the root node, and its children are n1, n4 and n6; n1's children are
+// n2 and n3; n4's child is n5; n6's child is n7. Nodes n0, n1 and n4 (marked
+// with a trailing "-") are partial keys, and nodes n2, n3, n5, n6 and n7
+// (marked with a trailing "+") are complete keys.
+type trieNode struct {
+ // value is the value of the trie node's key/value pair. It is empty if
+ // this node is not a complete key.
+ value string
+ // priority is the priority (higher is more important) of the trie node's
+ // key/value pair; keys are not necessarily matched shortest- or longest-
+ // first. Priority is positive if this node is a complete key, and zero
+ // otherwise. In the example above, positive/zero priorities are marked
+ // with a trailing "+" or "-".
+ priority int
+
+ // A trie node may have zero, one or more child nodes:
+ // * if the remaining fields are zero, there are no children.
+ // * if prefix and next are non-zero, there is one child in next.
+ // * if table is non-zero, it defines all the children.
+ //
+ // Prefixes are preferred over tables when there is one child, but the
+ // root node always uses a table for lookup efficiency.
+
+ // prefix is the difference in keys between this trie node and the next.
+ // In the example above, node n4 has prefix "cbc" and n4's next node is n5.
+ // Node n5 has no children and so has zero prefix, next and table fields.
+ prefix string
+ next *trieNode
+
+ // table is a lookup table indexed by the next byte in the key, after
+ // remapping that byte through genericReplacer.mapping to create a dense
+ // index. In the example above, the keys only use 'a', 'b', 'c', 'x' and
+ // 'y', which remap to 0, 1, 2, 3 and 4. All other bytes remap to 5, and
+ // genericReplacer.tableSize will be 5. Node n0's table will be
+ // []*trieNode{ 0:n1, 1:n4, 3:n6 }, where the 0, 1 and 3 are the remapped
+ // 'a', 'b' and 'x'.
+ table []*trieNode
+}
+
+func (t *trieNode) add(key, val string, priority int, r *genericReplacer) {
+ if key == "" {
+ if t.priority == 0 {
+ t.value = val
+ t.priority = priority
+ }
+ return
+ }
+
+ if t.prefix != "" {
+ // Need to split the prefix among multiple nodes.
+ var n int // length of the longest common prefix
+ for ; n < len(t.prefix) && n < len(key); n++ {
+ if t.prefix[n] != key[n] {
+ break
+ }
+ }
+ if n == len(t.prefix) {
+ t.next.add(key[n:], val, priority, r)
+ } else if n == 0 {
+ // First byte differs, start a new lookup table here. Looking up
+ // what is currently t.prefix[0] will lead to prefixNode, and
+ // looking up key[0] will lead to keyNode.
+ var prefixNode *trieNode
+ if len(t.prefix) == 1 {
+ prefixNode = t.next
+ } else {
+ prefixNode = &trieNode{
+ prefix: t.prefix[1:],
+ next: t.next,
+ }
+ }
+ keyNode := new(trieNode)
+ t.table = make([]*trieNode, r.tableSize)
+ t.table[r.mapping[t.prefix[0]]] = prefixNode
+ t.table[r.mapping[key[0]]] = keyNode
+ t.prefix = ""
+ t.next = nil
+ keyNode.add(key[1:], val, priority, r)
+ } else {
+ // Insert new node after the common section of the prefix.
+ next := &trieNode{
+ prefix: t.prefix[n:],
+ next: t.next,
+ }
+ t.prefix = t.prefix[:n]
+ t.next = next
+ next.add(key[n:], val, priority, r)
+ }
+ } else if t.table != nil {
+ // Insert into existing table.
+ m := r.mapping[key[0]]
+ if t.table[m] == nil {
+ t.table[m] = new(trieNode)
+ }
+ t.table[m].add(key[1:], val, priority, r)
+ } else {
+ t.prefix = key
+ t.next = new(trieNode)
+ t.next.add("", val, priority, r)
+ }
+}
+
+func (r *genericReplacer) lookup(s string, ignoreRoot bool) (val string, keylen int, found bool) {
+ // Iterate down the trie to the end, and grab the value and keylen with
+ // the highest priority.
+ bestPriority := 0
+ node := &r.root
+ n := 0
+ for node != nil {
+ if node.priority > bestPriority && !(ignoreRoot && node == &r.root) {
+ bestPriority = node.priority
+ val = node.value
+ keylen = n
+ found = true
+ }
+
+ if s == "" {
+ break
+ }
+ if node.table != nil {
+ index := r.mapping[s[0]]
+ if int(index) == r.tableSize {
+ break
+ }
+ node = node.table[index]
+ s = s[1:]
+ n++
+ } else if node.prefix != "" && HasPrefix(s, node.prefix) {
+ n += len(node.prefix)
+ s = s[len(node.prefix):]
+ node = node.next
+ } else {
+ break
+ }
+ }
+ return
+}
+
+// genericReplacer is the fully generic algorithm.
// It's used as a fallback when nothing faster can be used.
type genericReplacer struct {
- p []pair
+ root trieNode
+ // tableSize is the size of a trie node's lookup table. It is the number
+ // of unique key bytes.
+ tableSize int
+ // mapping maps from key bytes to a dense index for trieNode.table.
+ mapping [256]byte
}
-type pair struct{ old, new string }
+func makeGenericReplacer(oldnew []string) *genericReplacer {
+ r := new(genericReplacer)
+ // Find each byte used, then assign them each an index.
+ for i := 0; i < len(oldnew); i += 2 {
+ key := oldnew[i]
+ for j := 0; j < len(key); j++ {
+ r.mapping[key[j]] = 1
+ }
+ }
+
+ for _, b := range r.mapping {
+ r.tableSize += int(b)
+ }
+
+ var index byte
+ for i, b := range r.mapping {
+ if b == 0 {
+ r.mapping[i] = byte(r.tableSize)
+ } else {
+ r.mapping[i] = index
+ index++
+ }
+ }
+ // Ensure root node uses a lookup table (for performance).
+ r.root.table = make([]*trieNode, r.tableSize)
-type appendSliceWriter struct {
- b []byte
+ for i := 0; i < len(oldnew); i += 2 {
+ r.root.add(oldnew[i], oldnew[i+1], len(oldnew)-i, r)
+ }
+ return r
}
+type appendSliceWriter []byte
+
+// Write writes to the buffer to satisfy io.Writer.
func (w *appendSliceWriter) Write(p []byte) (int, error) {
- w.b = append(w.b, p...)
+ *w = append(*w, p...)
return len(p), nil
}
+// WriteString writes to the buffer without string->[]byte->string allocations.
+func (w *appendSliceWriter) WriteString(s string) (int, error) {
+ *w = append(*w, s...)
+ return len(s), nil
+}
+
+type stringWriterIface interface {
+ WriteString(string) (int, error)
+}
+
+type stringWriter struct {
+ w io.Writer
+}
+
+func (w stringWriter) WriteString(s string) (int, error) {
+ return w.w.Write([]byte(s))
+}
+
+func getStringWriter(w io.Writer) stringWriterIface {
+ sw, ok := w.(stringWriterIface)
+ if !ok {
+ sw = stringWriter{w}
+ }
+ return sw
+}
+
func (r *genericReplacer) Replace(s string) string {
- // TODO(bradfitz): optimized version
- n, _ := r.WriteString(discard, s)
- w := appendSliceWriter{make([]byte, 0, n)}
- r.WriteString(&w, s)
- return string(w.b)
+ buf := make(appendSliceWriter, 0, len(s))
+ r.WriteString(&buf, s)
+ return string(buf)
}
func (r *genericReplacer) WriteString(w io.Writer, s string) (n int, err error) {
- lastEmpty := false // the last replacement was of the empty string
-Input:
- // TODO(bradfitz): optimized version
- for i := 0; i < len(s); {
- for _, p := range r.p {
- if p.old == "" && lastEmpty {
- // Don't let old match twice in a row.
- // (it doesn't advance the input and
- // would otherwise loop forever)
- continue
+ sw := getStringWriter(w)
+ var last, wn int
+ var prevMatchEmpty bool
+ for i := 0; i <= len(s); {
+ // Ignore the empty match iff the previous loop found the empty match.
+ val, keylen, match := r.lookup(s[i:], prevMatchEmpty)
+ prevMatchEmpty = match && keylen == 0
+ if match {
+ wn, err = sw.WriteString(s[last:i])
+ n += wn
+ if err != nil {
+ return
}
- if HasPrefix(s[i:], p.old) {
- if p.new != "" {
- wn, err := w.Write([]byte(p.new))
- n += wn
- if err != nil {
- return n, err
- }
- }
- i += len(p.old)
- lastEmpty = p.old == ""
- continue Input
+ wn, err = sw.WriteString(val)
+ n += wn
+ if err != nil {
+ return
}
- }
- wn, err := w.Write([]byte{s[i]})
- n += wn
- if err != nil {
- return n, err
+ i += keylen
+ last = i
+ continue
}
i++
}
+ if last != len(s) {
+ wn, err = sw.WriteString(s[last:])
+ n += wn
+ }
+ return
+}
- // Final empty match at end.
- for _, p := range r.p {
- if p.old == "" {
- if p.new != "" {
- wn, err := w.Write([]byte(p.new))
- n += wn
- if err != nil {
- return n, err
- }
- }
+// singleStringReplacer is the implementation that's used when there is only
+// one string to replace (and that string has more than one byte).
+type singleStringReplacer struct {
+ finder *stringFinder
+ // value is the new string that replaces that pattern when it's found.
+ value string
+}
+
+func makeSingleStringReplacer(pattern string, value string) *singleStringReplacer {
+ return &singleStringReplacer{finder: makeStringFinder(pattern), value: value}
+}
+
+func (r *singleStringReplacer) Replace(s string) string {
+ var buf []byte
+ i := 0
+ for {
+ match := r.finder.next(s[i:])
+ if match == -1 {
break
}
+ buf = append(buf, s[i:i+match]...)
+ buf = append(buf, r.value...)
+ i += match + len(r.finder.pattern)
+ }
+ if buf == nil {
+ return s
}
+ buf = append(buf, s[i:]...)
+ return string(buf)
+}
- return n, nil
+func (r *singleStringReplacer) WriteString(w io.Writer, s string) (n int, err error) {
+ sw := getStringWriter(w)
+ var i, wn int
+ for {
+ match := r.finder.next(s[i:])
+ if match == -1 {
+ break
+ }
+ wn, err = sw.WriteString(s[i : i+match])
+ n += wn
+ if err != nil {
+ return
+ }
+ wn, err = sw.WriteString(r.value)
+ n += wn
+ if err != nil {
+ return
+ }
+ i += match + len(r.finder.pattern)
+ }
+ wn, err = sw.WriteString(s[i:])
+ n += wn
+ return
}
// byteReplacer is the implementation that's used when all the "old"
@@ -301,12 +546,3 @@ func (r *byteStringReplacer) WriteString(w io.Writer, s string) (n int, err erro
}
return n, nil
}
-
-// strings is too low-level to import io/ioutil
-var discard io.Writer = devNull(0)
-
-type devNull int
-
-func (devNull) Write(p []byte) (int, error) {
- return len(p), nil
-}
generated by cgit v1.2.3 (git 2.39.1) at 2025-02-13 00:46:28 +0000