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