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78 lines
2.3 KiB
Go
78 lines
2.3 KiB
Go
// Copyright 2012 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 atom provides integer codes (also known as atoms) for a fixed set of
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// frequently occurring HTML strings: tag names and attribute keys such as "p"
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// and "id".
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//
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// Sharing an atom's name between all elements with the same tag can result in
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// fewer string allocations when tokenizing and parsing HTML. Integer
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// comparisons are also generally faster than string comparisons.
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//
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// The value of an atom's particular code is not guaranteed to stay the same
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// between versions of this package. Neither is any ordering guaranteed:
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// whether atom.H1 < atom.H2 may also change. The codes are not guaranteed to
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// be dense. The only guarantees are that e.g. looking up "div" will yield
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// atom.Div, calling atom.Div.String will return "div", and atom.Div != 0.
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package atom // import "golang.org/x/net/html/atom"
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// Atom is an integer code for a string. The zero value maps to "".
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type Atom uint32
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// String returns the atom's name.
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func (a Atom) String() string {
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start := uint32(a >> 8)
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n := uint32(a & 0xff)
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if start+n > uint32(len(atomText)) {
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return ""
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}
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return atomText[start : start+n]
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}
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func (a Atom) string() string {
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return atomText[a>>8 : a>>8+a&0xff]
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}
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// fnv computes the FNV hash with an arbitrary starting value h.
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func fnv(h uint32, s []byte) uint32 {
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for i := range s {
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h ^= uint32(s[i])
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h *= 16777619
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}
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return h
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}
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func match(s string, t []byte) bool {
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for i, c := range t {
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if s[i] != c {
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return false
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}
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}
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return true
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}
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// Lookup returns the atom whose name is s. It returns zero if there is no
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// such atom. The lookup is case sensitive.
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func Lookup(s []byte) Atom {
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if len(s) == 0 || len(s) > maxAtomLen {
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return 0
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}
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h := fnv(hash0, s)
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if a := table[h&uint32(len(table)-1)]; int(a&0xff) == len(s) && match(a.string(), s) {
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return a
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}
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if a := table[(h>>16)&uint32(len(table)-1)]; int(a&0xff) == len(s) && match(a.string(), s) {
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return a
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}
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return 0
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}
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// String returns a string whose contents are equal to s. In that sense, it is
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// equivalent to string(s) but may be more efficient.
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func String(s []byte) string {
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if a := Lookup(s); a != 0 {
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return a.String()
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}
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return string(s)
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}
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