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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.
package build
import (
"fmt"
"io"
"reflect"
"sort"
"strings"
)
// This file contains code for detecting contractions and generating
// the necessary tables.
// Any Unicode Collation Algorithm (UCA) table entry that has more than
// one rune one the left-hand side is called a contraction.
// See http://www.unicode.org/reports/tr10/#Contractions for more details.
//
// We define the following terms:
// initial: a rune that appears as the first rune in a contraction.
// suffix: a sequence of runes succeeding the initial rune
// in a given contraction.
// non-initial: a rune that appears in a suffix.
//
// A rune may be both a initial and a non-initial and may be so in
// many contractions. An initial may typically also appear by itself.
// In case of ambiguities, the UCA requires we match the longest
// contraction.
//
// Many contraction rules share the same set of possible suffixes.
// We store sets of suffixes in a trie that associates an index with
// each suffix in the set. This index can be used to look up a
// collation element associated with the (starter rune, suffix) pair.
//
// The trie is defined on a UTF-8 byte sequence.
// The overall trie is represented as an array of ctEntries. Each node of the trie
// is represented as a subsequence of ctEntries, where each entry corresponds to
// a possible match of a next character in the search string. An entry
// also includes the length and offset to the next sequence of entries
// to check in case of a match.
const (
final = 0
noIndex = 0xFF
)
// ctEntry associates to a matching byte an offset and/or next sequence of
// bytes to check. A ctEntry c is called final if a match means that the
// longest suffix has been found. An entry c is final if c.n == 0.
// A single final entry can match a range of characters to an offset.
// A non-final entry always matches a single byte. Note that a non-final
// entry might still resemble a completed suffix.
// Examples:
// The suffix strings "ab" and "ac" can be represented as:
// []ctEntry{
// {'a', 1, 1, noIndex}, // 'a' by itself does not match, so i is 0xFF.
// {'b', 'c', 0, 1}, // "ab" -> 1, "ac" -> 2
// }
//
// The suffix strings "ab", "abc", "abd", and "abcd" can be represented as:
// []ctEntry{
// {'a', 1, 1, noIndex}, // 'a' must be followed by 'b'.
// {'b', 1, 2, 1}, // "ab" -> 1, may be followed by 'c' or 'd'.
// {'d', 'd', final, 3}, // "abd" -> 3
// {'c', 4, 1, 2}, // "abc" -> 2, may be followed by 'd'.
// {'d', 'd', final, 4}, // "abcd" -> 4
// }
// See genStateTests in contract_test.go for more examples.
type ctEntry struct {
l uint8 // non-final: byte value to match; final: lowest match in range.
h uint8 // non-final: relative index to next block; final: highest match in range.
n uint8 // non-final: length of next block; final: final
i uint8 // result offset. Will be noIndex if more bytes are needed to complete.
}
// contractTrieSet holds a set of contraction tries. The tries are stored
// consecutively in the entry field.
type contractTrieSet []struct{ l, h, n, i uint8 }
// ctHandle is used to identify a trie in the trie set, consisting in an offset
// in the array and the size of the first node.
type ctHandle struct {
index, n int
}
// appendTrie adds a new trie for the given suffixes to the trie set and returns
// a handle to it. The handle will be invalid on error.
func (ct *contractTrieSet) appendTrie(suffixes []string) (ctHandle, error) {
es := make([]stridx, len(suffixes))
for i, s := range suffixes {
es[i].str = s
}
sort.Sort(offsetSort(es))
for i := range es {
es[i].index = i + 1
}
sort.Sort(genidxSort(es))
i := len(*ct)
n, err := ct.genStates(es)
if err != nil {
*ct = (*ct)[:i]
return ctHandle{}, err
}
return ctHandle{i, n}, nil
}
// genStates generates ctEntries for a given suffix set and returns
// the number of entries for the first node.
func (ct *contractTrieSet) genStates(sis []stridx) (int, error) {
if len(sis) == 0 {
return 0, fmt.Errorf("genStates: list of suffices must be non-empty")
}
start := len(*ct)
// create entries for differing first bytes.
for _, si := range sis {
s := si.str
if len(s) == 0 {
continue
}
added := false
c := s[0]
if len(s) > 1 {
for j := len(*ct) - 1; j >= start; j-- {
if (*ct)[j].l == c {
added = true
break
}
}
if !added {
*ct = append(*ct, ctEntry{l: c, i: noIndex})
}
} else {
for j := len(*ct) - 1; j >= start; j-- {
// Update the offset for longer suffixes with the same byte.
if (*ct)[j].l == c {
(*ct)[j].i = uint8(si.index)
added = true
}
// Extend range of final ctEntry, if possible.
if (*ct)[j].h+1 == c {
(*ct)[j].h = c
added = true
}
}
if !added {
*ct = append(*ct, ctEntry{l: c, h: c, n: final, i: uint8(si.index)})
}
}
}
n := len(*ct) - start
// Append nodes for the remainder of the suffixes for each ctEntry.
sp := 0
for i, end := start, len(*ct); i < end; i++ {
fe := (*ct)[i]
if fe.h == 0 { // uninitialized non-final
ln := len(*ct) - start - n
if ln > 0xFF {
return 0, fmt.Errorf("genStates: relative block offset too large: %d > 255", ln)
}
fe.h = uint8(ln)
// Find first non-final strings with same byte as current entry.
for ; sis[sp].str[0] != fe.l; sp++ {
}
se := sp + 1
for ; se < len(sis) && len(sis[se].str) > 1 && sis[se].str[0] == fe.l; se++ {
}
sl := sis[sp:se]
sp = se
for i, si := range sl {
sl[i].str = si.str[1:]
}
nn, err := ct.genStates(sl)
if err != nil {
return 0, err
}
fe.n = uint8(nn)
(*ct)[i] = fe
}
}
sort.Sort(entrySort((*ct)[start : start+n]))
return n, nil
}
// There may be both a final and non-final entry for a byte if the byte
// is implied in a range of matches in the final entry.
// We need to ensure that the non-final entry comes first in that case.
type entrySort contractTrieSet
func (fe entrySort) Len() int { return len(fe) }
func (fe entrySort) Swap(i, j int) { fe[i], fe[j] = fe[j], fe[i] }
func (fe entrySort) Less(i, j int) bool {
return fe[i].l > fe[j].l
}
// stridx is used for sorting suffixes and their associated offsets.
type stridx struct {
str string
index int
}
// For computing the offsets, we first sort by size, and then by string.
// This ensures that strings that only differ in the last byte by 1
// are sorted consecutively in increasing order such that they can
// be packed as a range in a final ctEntry.
type offsetSort []stridx
func (si offsetSort) Len() int { return len(si) }
func (si offsetSort) Swap(i, j int) { si[i], si[j] = si[j], si[i] }
func (si offsetSort) Less(i, j int) bool {
if len(si[i].str) != len(si[j].str) {
return len(si[i].str) > len(si[j].str)
}
return si[i].str < si[j].str
}
// For indexing, we want to ensure that strings are sorted in string order, where
// for strings with the same prefix, we put longer strings before shorter ones.
type genidxSort []stridx
func (si genidxSort) Len() int { return len(si) }
func (si genidxSort) Swap(i, j int) { si[i], si[j] = si[j], si[i] }
func (si genidxSort) Less(i, j int) bool {
if strings.HasPrefix(si[j].str, si[i].str) {
return false
}
if strings.HasPrefix(si[i].str, si[j].str) {
return true
}
return si[i].str < si[j].str
}
// lookup matches the longest suffix in str and returns the associated offset
// and the number of bytes consumed.
func (ct *contractTrieSet) lookup(h ctHandle, str []byte) (index, ns int) {
states := (*ct)[h.index:]
p := 0
n := h.n
for i := 0; i < n && p < len(str); {
e := states[i]
c := str[p]
if c >= e.l {
if e.l == c {
p++
if e.i != noIndex {
index, ns = int(e.i), p
}
if e.n != final {
// set to new state
i, states, n = 0, states[int(e.h)+n:], int(e.n)
} else {
return
}
continue
} else if e.n == final && c <= e.h {
p++
return int(c-e.l) + int(e.i), p
}
}
i++
}
return
}
// print writes the contractTrieSet t as compilable Go code to w. It returns
// the total number of bytes written and the size of the resulting data structure in bytes.
func (t *contractTrieSet) print(w io.Writer, name string) (n, size int, err error) {
update3 := func(nn, sz int, e error) {
n += nn
if err == nil {
err = e
}
size += sz
}
update2 := func(nn int, e error) { update3(nn, 0, e) }
update3(t.printArray(w, name))
update2(fmt.Fprintf(w, "var %sContractTrieSet = ", name))
update3(t.printStruct(w, name))
update2(fmt.Fprintln(w))
return
}
func (ct contractTrieSet) printArray(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
}
}
size = len(ct) * 4
p("// %sCTEntries: %d entries, %d bytes\n", name, len(ct), size)
p("var %sCTEntries = [%d]struct{l,h,n,i uint8}{\n", name, len(ct))
for _, fe := range ct {
p("\t{0x%X, 0x%X, %d, %d},\n", fe.l, fe.h, fe.n, fe.i)
}
p("}\n")
return
}
func (ct contractTrieSet) printStruct(w io.Writer, name string) (n, size int, err error) {
n, err = fmt.Fprintf(w, "contractTrieSet( %sCTEntries[:] )", name)
size = int(reflect.TypeOf(ct).Size())
return
}