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mirror of https://github.com/golang/go synced 2024-11-22 04:24:39 -07:00

exp/html/atom: faster Lookup with smaller tables

Use perfect cuckoo hash, to avoid binary search.
Define Atom bits as offset+len in long string instead
of enumeration, to avoid string headers.

Before: 1909 string bytes + 6060 tables = 7969 total data
After: 1406 string bytes + 2048 tables = 3454 total data

benchmark          old ns/op    new ns/op    delta
BenchmarkLookup        83878        64681  -22.89%

R=nigeltao, r
CC=golang-dev
https://golang.org/cl/6262051
This commit is contained in:
Russ Cox 2012-06-02 22:43:11 -04:00
parent 911f802b37
commit 192550592a
5 changed files with 1216 additions and 1081 deletions

View File

@ -15,69 +15,64 @@
// 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.
//
// TODO(rsc): When this package moves out of exp we need to freeze atom values
// across releases.
package atom
// The hash function must be the same as the one used in gen.go
func hash(s []byte) (h uint32) {
for i := 0; i < len(s); i++ {
h = h<<5 ^ h>>27 ^ uint32(s[i])
// 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
}
// Atom is an integer code for a string. The zero value maps to "".
type Atom int
// String returns the atom's name.
func (a Atom) String() string {
if 0 <= a && a < Atom(len(table)) {
return table[a]
func match(s string, t []byte) bool {
for i, c := range t {
if s[i] != c {
return false
}
}
return ""
return true
}
// Lookup returns the atom whose name is s. It returns zero if there is no
// such atom.
func Lookup(s []byte) Atom {
if len(s) == 0 || len(s) > maxLen {
if len(s) == 0 || len(s) > maxAtomLen {
return 0
}
if len(s) == 1 {
x := s[0]
if x < 'a' || x > 'z' {
return 0
}
return oneByteAtoms[x-'a']
h := fnv(hash0, s)
if a := table[h&uint32(len(table)-1)]; int(a&0xff) == len(s) && match(a.string(), s) {
return a
}
hs := hash(s)
// Binary search for hs. Unlike sort.Search, this returns early on an exact match.
// A loop invariant is that len(table[i]) == len(s) for all i in [lo, hi).
lo := Atom(loHi[len(s)])
hi := Atom(loHi[len(s)+1])
for lo < hi {
mid := (lo + hi) / 2
if ht := hashes[mid]; hs == ht {
// The gen.go program ensures that each atom's name has a distinct hash.
// However, arbitrary strings may collide with the atom's name. We have
// to check that string(s) == table[mid].
t := table[mid]
for i, si := range s {
if si != t[i] {
return 0
}
}
return mid
} else if hs > ht {
lo = mid + 1
} else {
hi = mid
}
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.
// equivalent to string(s) but may be more efficient.
func String(s []byte) string {
if a := Lookup(s); a != 0 {
return a.String()

View File

@ -9,11 +9,22 @@ import (
"testing"
)
func TestKnown(t *testing.T) {
for _, s := range testAtomList {
if atom := Lookup([]byte(s)); atom.String() != s {
t.Errorf("Lookup(%q) = %#x (%q)", s, uint32(atom), atom.String())
}
}
}
func TestHits(t *testing.T) {
for i, s := range table {
got := Lookup([]byte(s))
if got != Atom(i) {
t.Errorf("Lookup(%q): got %d, want %d", s, got, i)
for _, a := range table {
if a == 0 {
continue
}
got := Lookup([]byte(a.String()))
if got != a {
t.Errorf("Lookup(%q) = %#x, want %#x", a.String(), uint32(got), uint32(a))
}
}
}
@ -55,8 +66,12 @@ func TestMisses(t *testing.T) {
}
func BenchmarkLookup(b *testing.B) {
sortedTable := make([]string, len(table))
copy(sortedTable, table[:])
sortedTable := make([]string, 0, len(table))
for _, a := range table {
if a != 0 {
sortedTable = append(sortedTable, a.String())
}
}
sort.Strings(sortedTable)
x := make([][]byte, 1000)

View File

@ -6,37 +6,21 @@
package main
// This program generates table.go
// This program generates table.go and table_test.go.
// Invoke as
//
// go run gen.go |gofmt >table.go
// go run gen.go -test |gofmt >table_test.go
import (
"flag"
"fmt"
"math/rand"
"os"
"sort"
"strings"
)
// The hash function must be the same as the one used in atom.go
func hash(s string) (h uint32) {
for i := 0; i < len(s); i++ {
h = h<<5 ^ h>>27 ^ uint32(s[i])
}
return h
}
// lhash returns a uint64 whose high 32 bits are len(s) and whose low 32 bits
// are hash(s).
func lhash(s string) uint64 {
return uint64(len(s))<<32 | uint64(hash(s))
}
type byLhash []string
func (b byLhash) Len() int { return len(b) }
func (b byLhash) Less(i, j int) bool { return lhash(b[i]) < lhash(b[j]) }
func (b byLhash) Swap(i, j int) { b[i], b[j] = b[j], b[i] }
// identifier converts s to a Go exported identifier.
// It converts "div" to "Div" and "accept-charset" to "AcceptCharset".
func identifier(s string) string {
@ -56,94 +40,247 @@ func identifier(s string) string {
return string(b)
}
var test = flag.Bool("test", false, "generate table_test.go")
func main() {
// Construct a list of atoms, sorted by their lhash.
m0 := map[string]bool{
"": true,
}
for _, list := range [][]string{elements, attributes, eventHandlers, extra} {
for _, s := range list {
m0[s] = true
}
}
atoms := make([]string, 0, len(m0))
for s := range m0 {
atoms = append(atoms, s)
}
sort.Sort(byLhash(atoms))
flag.Parse()
// Calculate the magic constants to output as table.go.
byInt := []string{}
byStr := map[string]int{}
ident := []string{}
lhashes := []uint64{}
var all []string
all = append(all, elements...)
all = append(all, attributes...)
all = append(all, eventHandlers...)
all = append(all, extra...)
sort.Strings(all)
if *test {
fmt.Printf("// generated by go run gen.go -test; DO NOT EDIT\n\n")
fmt.Printf("package atom\n\n")
fmt.Printf("var testAtomList = []string{\n")
for _, s := range all {
fmt.Printf("\t%q,\n", s)
}
fmt.Printf("}\n")
return
}
// uniq - lists have dups
// compute max len too
maxLen := 0
for i, s := range atoms {
byInt = append(byInt, s)
byStr[s] = i
ident = append(ident, identifier(s))
lhashes = append(lhashes, lhash(s))
if maxLen < len(s) {
maxLen = len(s)
w := 0
for _, s := range all {
if w == 0 || all[w-1] != s {
if maxLen < len(s) {
maxLen = len(s)
}
all[w] = s
w++
}
}
all = all[:w]
// Find hash that minimizes table size.
var best *table
for i := 0; i < 1000000; i++ {
if best != nil && 1<<(best.k-1) < len(all) {
break
}
h := rand.Uint32()
for k := uint(0); k <= 16; k++ {
if best != nil && k >= best.k {
break
}
var t table
if t.init(h, k, all) {
best = &t
break
}
}
}
if best == nil {
fmt.Fprintf(os.Stderr, "failed to construct string table\n")
os.Exit(1)
}
// Lay out strings, using overlaps when possible.
layout := append([]string{}, all...)
// Remove strings that are substrings of other strings
for changed := true; changed; {
changed = false
for i, s := range layout {
if s == "" {
continue
}
for j, t := range layout {
if i != j && t != "" && strings.Contains(s, t) {
changed = true
layout[j] = ""
}
}
}
}
// Check for hash collisions.
m1 := map[uint64]int{}
for i, h := range lhashes {
h &= 1<<32 - 1
if j, ok := m1[h]; ok {
fmt.Fprintf(os.Stderr, "hash collision at 0x%08x: %q, %q\n", h, byInt[i], byInt[j])
os.Exit(1)
// Join strings where one suffix matches another prefix.
for {
// Find best i, j, k such that layout[i][len-k:] == layout[j][:k],
// maximizing overlap length k.
besti := -1
bestj := -1
bestk := 0
for i, s := range layout {
if s == "" {
continue
}
for j, t := range layout {
if i == j {
continue
}
for k := bestk + 1; k <= len(s) && k <= len(t); k++ {
if s[len(s)-k:] == t[:k] {
besti = i
bestj = j
bestk = k
}
}
}
}
m1[h] = i
if bestk > 0 {
layout[besti] += layout[bestj][bestk:]
layout[bestj] = ""
continue
}
break
}
text := strings.Join(layout, "")
atom := map[string]uint32{}
for _, s := range all {
off := strings.Index(text, s)
if off < 0 {
panic("lost string " + s)
}
atom[s] = uint32(off<<8 | len(s))
}
// Generate the Go code.
fmt.Printf("// generated by go run gen.go; DO NOT EDIT\n\n")
fmt.Printf("package atom\n\nconst (\n")
{
// Print the Atoms in alphabetical order.
lines := []string{}
for i, _ := range byInt {
if i == 0 {
continue
}
lines = append(lines, fmt.Sprintf("\t%s Atom = %d", ident[i], i))
for _, s := range all {
fmt.Printf("\t%s Atom = %#x\n", identifier(s), atom[s])
}
fmt.Printf(")\n\n")
fmt.Printf("const hash0 = %#x\n\n", best.h0)
fmt.Printf("const maxAtomLen = %d\n\n", maxLen)
fmt.Printf("var table = [1<<%d]Atom{\n", best.k)
for i, s := range best.tab {
if s == "" {
continue
}
sort.Strings(lines)
for _, line := range lines {
fmt.Println(line)
fmt.Printf("\t%#x: %#x, // %s\n", i, atom[s], s)
}
fmt.Printf("}\n")
datasize := (1 << best.k) * 4
fmt.Printf("const atomText =\n")
textsize := len(text)
for len(text) > 60 {
fmt.Printf("\t%q +\n", text[:60])
text = text[60:]
}
fmt.Printf("\t%q\n\n", text)
fmt.Fprintf(os.Stderr, "%d atoms; %d string bytes + %d tables = %d total data\n", len(all), textsize, datasize, textsize+datasize)
}
type byLen []string
func (x byLen) Less(i, j int) bool { return len(x[i]) > len(x[j]) }
func (x byLen) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
func (x byLen) Len() int { return len(x) }
// fnv computes the FNV hash with an arbitrary starting value h.
func fnv(h uint32, s string) uint32 {
for i := 0; i < len(s); i++ {
h ^= uint32(s[i])
h *= 16777619
}
return h
}
// A table represents an attempt at constructing the lookup table.
// The lookup table uses cuckoo hashing, meaning that each string
// can be found in one of two positions.
type table struct {
h0 uint32
k uint
mask uint32
tab []string
}
// hash returns the two hashes for s.
func (t *table) hash(s string) (h1, h2 uint32) {
h := fnv(t.h0, s)
h1 = h & t.mask
h2 = (h >> 16) & t.mask
return
}
// init initializes the table with the given parameters.
// h0 is the initial hash value,
// k is the number of bits of hash value to use, and
// x is the list of strings to store in the table.
// init returns false if the table cannot be constructed.
func (t *table) init(h0 uint32, k uint, x []string) bool {
t.h0 = h0
t.k = k
t.tab = make([]string, 1<<k)
t.mask = 1<<k - 1
for _, s := range x {
if !t.insert(s) {
return false
}
fmt.Printf(")\n\n")
}
fmt.Printf("const maxLen = %d\n\n", maxLen)
fmt.Printf("var table = [...]string{\n")
for _, s := range byInt {
fmt.Printf("\t%q,\n", s)
return true
}
// insert inserts s in the table.
func (t *table) insert(s string) bool {
h1, h2 := t.hash(s)
if t.tab[h1] == "" {
t.tab[h1] = s
return true
}
fmt.Printf("}\n\n")
fmt.Printf("var hashes = [...]uint32{\n")
for _, s := range byInt {
fmt.Printf("\t0x%08x,\n", hash(s))
if t.tab[h2] == "" {
t.tab[h2] = s
return true
}
fmt.Printf("}\n\n")
fmt.Printf("var loHi = [maxLen + 2]uint16{\n")
for n := 0; n <= maxLen; n++ {
fmt.Printf("\t%d,\n", sort.Search(len(byInt), func(i int) bool {
return int(lhashes[i]>>32) >= n
}))
if t.push(h1, 0) {
t.tab[h1] = s
return true
}
fmt.Printf("\t%d,\n", len(byInt))
fmt.Printf("}\n\n")
fmt.Printf("var oneByteAtoms = [26]Atom{\n")
for i := 'a'; i <= 'z'; i++ {
val := "0"
if x := byStr[string(i)]; x != 0 {
val = ident[x]
}
fmt.Printf("\t%s,\n", val)
if t.push(h2, 0) {
t.tab[h2] = s
return true
}
fmt.Printf("}\n\n")
return false
}
// push attempts to push aside the entry in slot i.
func (t *table) push(i uint32, depth int) bool {
if depth > len(t.tab) {
return false
}
s := t.tab[i]
h1, h2 := t.hash(s)
j := h1 + h2 - i
if t.tab[j] != "" && !t.push(j, depth+1) {
return false
}
t.tab[j] = s
return true
}
// The lists of element names and attribute keys were taken from

File diff suppressed because it is too large Load Diff

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@ -0,0 +1,309 @@
// generated by go run gen.go -test; DO NOT EDIT
package atom
var testAtomList = []string{
"a",
"abbr",
"accept",
"accept-charset",
"accesskey",
"action",
"address",
"align",
"alt",
"annotation",
"applet",
"area",
"article",
"aside",
"async",
"audio",
"autocomplete",
"autofocus",
"autoplay",
"b",
"base",
"bdi",
"bdo",
"blockquote",
"body",
"border",
"br",
"button",
"canvas",
"caption",
"center",
"challenge",
"charset",
"checked",
"cite",
"cite",
"class",
"code",
"col",
"colgroup",
"color",
"cols",
"colspan",
"command",
"command",
"content",
"contenteditable",
"contextmenu",
"controls",
"coords",
"crossorigin",
"data",
"data",
"datalist",
"datetime",
"dd",
"default",
"defer",
"del",
"details",
"dfn",
"dialog",
"dir",
"dirname",
"disabled",
"div",
"dl",
"download",
"draggable",
"dropzone",
"dt",
"em",
"embed",
"enctype",
"fieldset",
"figcaption",
"figure",
"font",
"footer",
"for",
"form",
"form",
"formaction",
"formenctype",
"formmethod",
"formnovalidate",
"formtarget",
"frame",
"frameset",
"h1",
"h2",
"h3",
"h4",
"h5",
"h6",
"head",
"header",
"headers",
"height",
"hgroup",
"hidden",
"high",
"hr",
"href",
"hreflang",
"html",
"http-equiv",
"i",
"icon",
"id",
"iframe",
"img",
"inert",
"input",
"ins",
"ismap",
"itemid",
"itemprop",
"itemref",
"itemscope",
"itemtype",
"kbd",
"keygen",
"keytype",
"kind",
"label",
"label",
"lang",
"legend",
"li",
"link",
"list",
"loop",
"low",
"manifest",
"map",
"mark",
"max",
"maxlength",
"media",
"mediagroup",
"menu",
"meta",
"meter",
"method",
"min",
"multiple",
"muted",
"name",
"nav",
"nobr",
"noscript",
"novalidate",
"object",
"ol",
"onabort",
"onafterprint",
"onbeforeprint",
"onbeforeunload",
"onblur",
"oncancel",
"oncanplay",
"oncanplaythrough",
"onchange",
"onclick",
"onclose",
"oncontextmenu",
"oncuechange",
"ondblclick",
"ondrag",
"ondragend",
"ondragenter",
"ondragleave",
"ondragover",
"ondragstart",
"ondrop",
"ondurationchange",
"onemptied",
"onended",
"onerror",
"onfocus",
"onhashchange",
"oninput",
"oninvalid",
"onkeydown",
"onkeypress",
"onkeyup",
"onload",
"onloadeddata",
"onloadedmetadata",
"onloadstart",
"onmessage",
"onmousedown",
"onmousemove",
"onmouseout",
"onmouseover",
"onmouseup",
"onmousewheel",
"onoffline",
"ononline",
"onpagehide",
"onpageshow",
"onpause",
"onplay",
"onplaying",
"onpopstate",
"onprogress",
"onratechange",
"onreset",
"onresize",
"onscroll",
"onseeked",
"onseeking",
"onselect",
"onshow",
"onstalled",
"onstorage",
"onsubmit",
"onsuspend",
"ontimeupdate",
"onunload",
"onvolumechange",
"onwaiting",
"open",
"optgroup",
"optimum",
"option",
"output",
"p",
"param",
"pattern",
"ping",
"placeholder",
"poster",
"pre",
"preload",
"progress",
"q",
"radiogroup",
"readonly",
"rel",
"required",
"reversed",
"rows",
"rowspan",
"rp",
"rt",
"ruby",
"s",
"samp",
"sandbox",
"scope",
"scoped",
"script",
"seamless",
"section",
"select",
"selected",
"shape",
"size",
"sizes",
"small",
"source",
"span",
"span",
"spellcheck",
"src",
"srcdoc",
"srclang",
"start",
"step",
"strong",
"style",
"style",
"sub",
"summary",
"sup",
"tabindex",
"table",
"target",
"tbody",
"td",
"textarea",
"tfoot",
"th",
"thead",
"time",
"title",
"title",
"tr",
"track",
"translate",
"type",
"typemustmatch",
"u",
"ul",
"usemap",
"value",
"var",
"video",
"wbr",
"width",
"wrap",
}