text: // 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)
  }
  