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// 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.
// The trie in this file is used to associate the first full character
// in a UTF-8 string to a collation element.
// All but the last byte in a UTF-8 byte sequence are
// used to look up offsets in the index table to be used for the next byte.
// The last byte is used to index into a table of collation elements.
// This file contains the code for the generation of the trie.
package build
import (
"fmt"
"hash/fnv"
"io"
"reflect"
)
const (
blockSize = 64
blockOffset = 2 // Subtract 2 blocks to compensate for the 0x80 added to continuation bytes.
)
type trieHandle struct {
lookupStart uint16 // offset in table for first byte
valueStart uint16 // offset in table for first byte
}
type trie struct {
index []uint16
values []uint32
}
// trieNode is the intermediate trie structure used for generating a trie.
type trieNode struct {
index []*trieNode
value []uint32
b byte
refValue uint16
refIndex uint16
}
func newNode() *trieNode {
return &trieNode{
index: make([]*trieNode, 64),
value: make([]uint32, 128), // root node size is 128 instead of 64
}
}
func (n *trieNode) isInternal() bool {
return n.value != nil
}
func (n *trieNode) insert(r rune, value uint32) {
const maskx = 0x3F // mask out two most-significant bits
str := string(r)
if len(str) == 1 {
n.value[str[0]] = value
return
}
for i := 0; i < len(str)-1; i++ {
b := str[i] & maskx
if n.index == nil {
n.index = make([]*trieNode, blockSize)
}
nn := n.index[b]
if nn == nil {
nn = &trieNode{}
nn.b = b
n.index[b] = nn
}
n = nn
}
if n.value == nil {
n.value = make([]uint32, blockSize)
}
b := str[len(str)-1] & maskx
n.value[b] = value
}
type trieBuilder struct {
t *trie
roots []*trieHandle
lookupBlocks []*trieNode
valueBlocks []*trieNode
lookupBlockIdx map[uint32]*trieNode
valueBlockIdx map[uint32]*trieNode
}
func newTrieBuilder() *trieBuilder {
index := &trieBuilder{}
index.lookupBlocks = make([]*trieNode, 0)
index.valueBlocks = make([]*trieNode, 0)
index.lookupBlockIdx = make(map[uint32]*trieNode)
index.valueBlockIdx = make(map[uint32]*trieNode)
// The third nil is the default null block. The other two blocks
// are used to guarantee an offset of at least 3 for each block.
index.lookupBlocks = append(index.lookupBlocks, nil, nil, nil)
index.t = &trie{}
return index
}
func (b *trieBuilder) computeOffsets(n *trieNode) *trieNode {
hasher := fnv.New32()
if n.index != nil {
for i, nn := range n.index {
var vi, vv uint16
if nn != nil {
nn = b.computeOffsets(nn)
n.index[i] = nn
vi = nn.refIndex
vv = nn.refValue
}
hasher.Write([]byte{byte(vi >> 8), byte(vi)})
hasher.Write([]byte{byte(vv >> 8), byte(vv)})
}
h := hasher.Sum32()
nn, ok := b.lookupBlockIdx[h]
if !ok {
n.refIndex = uint16(len(b.lookupBlocks)) - blockOffset
b.lookupBlocks = append(b.lookupBlocks, n)
b.lookupBlockIdx[h] = n
} else {
n = nn
}
} else {
for _, v := range n.value {
hasher.Write([]byte{byte(v >> 24), byte(v >> 16), byte(v >> 8), byte(v)})
}
h := hasher.Sum32()
nn, ok := b.valueBlockIdx[h]
if !ok {
n.refValue = uint16(len(b.valueBlocks)) - blockOffset
n.refIndex = n.refValue
b.valueBlocks = append(b.valueBlocks, n)
b.valueBlockIdx[h] = n
} else {
n = nn
}
}
return n
}
func (b *trieBuilder) addStartValueBlock(n *trieNode) uint16 {
hasher := fnv.New32()
for _, v := range n.value[:2*blockSize] {
hasher.Write([]byte{byte(v >> 24), byte(v >> 16), byte(v >> 8), byte(v)})
}
h := hasher.Sum32()
nn, ok := b.valueBlockIdx[h]
if !ok {
n.refValue = uint16(len(b.valueBlocks))
n.refIndex = n.refValue
b.valueBlocks = append(b.valueBlocks, n)
// Add a dummy block to accommodate the double block size.
b.valueBlocks = append(b.valueBlocks, nil)
b.valueBlockIdx[h] = n
} else {
n = nn
}
return n.refValue
}
func genValueBlock(t *trie, n *trieNode) {
if n != nil {
for _, v := range n.value {
t.values = append(t.values, v)
}
}
}
func genLookupBlock(t *trie, n *trieNode) {
for _, nn := range n.index {
v := uint16(0)
if nn != nil {
if n.index != nil {
v = nn.refIndex
} else {
v = nn.refValue
}
}
t.index = append(t.index, v)
}
}
func (b *trieBuilder) addTrie(n *trieNode) *trieHandle {
h := &trieHandle{}
b.roots = append(b.roots, h)
h.valueStart = b.addStartValueBlock(n)
if len(b.roots) == 1 {
// We insert a null block after the first start value block.
// This ensures that continuation bytes UTF-8 sequences of length
// greater than 2 will automatically hit a null block if there
// was an undefined entry.
b.valueBlocks = append(b.valueBlocks, nil)
}
n = b.computeOffsets(n)
// Offset by one extra block as the first byte starts at 0xC0 instead of 0x80.
h.lookupStart = n.refIndex - 1
return h
}
// generate generates and returns the trie for n.
func (b *trieBuilder) generate() (t *trie, err error) {
t = b.t
if len(b.valueBlocks) >= 1<<16 {
return nil, fmt.Errorf("maximum number of value blocks exceeded (%d > %d)", len(b.valueBlocks), 1<<16)
}
if len(b.lookupBlocks) >= 1<<16 {
return nil, fmt.Errorf("maximum number of lookup blocks exceeded (%d > %d)", len(b.lookupBlocks), 1<<16)
}
genValueBlock(t, b.valueBlocks[0])
genValueBlock(t, &trieNode{value: make([]uint32, 64)})
for i := 2; i < len(b.valueBlocks); i++ {
genValueBlock(t, b.valueBlocks[i])
}
n := &trieNode{index: make([]*trieNode, 64)}
genLookupBlock(t, n)
genLookupBlock(t, n)
genLookupBlock(t, n)
for i := 3; i < len(b.lookupBlocks); i++ {
genLookupBlock(t, b.lookupBlocks[i])
}
return b.t, nil
}
func (t *trie) printArrays(w io.Writer, name string) (n, size int, err error) {
p := func(f string, a ...interface{}) {
nn, e := fmt.Fprintf(w, f, a...)
n += nn
if err == nil {
err = e
}
}
nv := len(t.values)
p("// %sValues: %d entries, %d bytes\n", name, nv, nv*4)
p("// Block 2 is the null block.\n")
p("var %sValues = [%d]uint32 {", name, nv)
var printnewline bool
for i, v := range t.values {
if i%blockSize == 0 {
p("\n\t// Block %#x, offset %#x", i/blockSize, i)
}
if i%4 == 0 {
printnewline = true
}
if v != 0 {
if printnewline {
p("\n\t")
printnewline = false
}
p("%#04x:%#08x, ", i, v)
}
}
p("\n}\n\n")
ni := len(t.index)
p("// %sLookup: %d entries, %d bytes\n", name, ni, ni*2)
p("// Block 0 is the null block.\n")
p("var %sLookup = [%d]uint16 {", name, ni)
printnewline = false
for i, v := range t.index {
if i%blockSize == 0 {
p("\n\t// Block %#x, offset %#x", i/blockSize, i)
}
if i%8 == 0 {
printnewline = true
}
if v != 0 {
if printnewline {
p("\n\t")
printnewline = false
}
p("%#03x:%#02x, ", i, v)
}
}
p("\n}\n\n")
return n, nv*4 + ni*2, err
}
func (t *trie) printStruct(w io.Writer, handle *trieHandle, name string) (n, sz int, err error) {
const msg = "trie{ %sLookup[%d:], %sValues[%d:], %sLookup[:], %sValues[:]}"
n, err = fmt.Fprintf(w, msg, name, handle.lookupStart*blockSize, name, handle.valueStart*blockSize, name, name)
sz += int(reflect.TypeOf(trie{}).Size())
return
}
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