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160 lines
3.2 KiB
Go
160 lines
3.2 KiB
Go
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// The trie in this file is used to associate the first full character in an
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// UTF-8 string to a collation element. All but the last byte in a UTF-8 byte
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// sequence are used to lookup offsets in the index table to be used for the
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// next byte. The last byte is used to index into a table of collation elements.
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// For a full description, see go.text/collate/build/trie.go.
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package colltab
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const blockSize = 64
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type Trie struct {
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Index0 []uint16 // index for first byte (0xC0-0xFF)
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Values0 []uint32 // index for first byte (0x00-0x7F)
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Index []uint16
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Values []uint32
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}
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const (
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t1 = 0x00 // 0000 0000
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tx = 0x80 // 1000 0000
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t2 = 0xC0 // 1100 0000
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t3 = 0xE0 // 1110 0000
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t4 = 0xF0 // 1111 0000
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t5 = 0xF8 // 1111 1000
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t6 = 0xFC // 1111 1100
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te = 0xFE // 1111 1110
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)
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func (t *Trie) lookupValue(n uint16, b byte) Elem {
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return Elem(t.Values[int(n)<<6+int(b)])
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}
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// lookup returns the trie value for the first UTF-8 encoding in s and
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// the width in bytes of this encoding. The size will be 0 if s does not
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// hold enough bytes to complete the encoding. len(s) must be greater than 0.
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func (t *Trie) lookup(s []byte) (v Elem, sz int) {
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c0 := s[0]
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switch {
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case c0 < tx:
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return Elem(t.Values0[c0]), 1
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case c0 < t2:
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return 0, 1
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case c0 < t3:
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if len(s) < 2 {
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return 0, 0
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}
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i := t.Index0[c0]
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c1 := s[1]
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if c1 < tx || t2 <= c1 {
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return 0, 1
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}
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return t.lookupValue(i, c1), 2
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case c0 < t4:
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if len(s) < 3 {
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return 0, 0
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}
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i := t.Index0[c0]
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c1 := s[1]
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if c1 < tx || t2 <= c1 {
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return 0, 1
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}
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o := int(i)<<6 + int(c1)
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i = t.Index[o]
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c2 := s[2]
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if c2 < tx || t2 <= c2 {
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return 0, 2
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}
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return t.lookupValue(i, c2), 3
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case c0 < t5:
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if len(s) < 4 {
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return 0, 0
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}
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i := t.Index0[c0]
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c1 := s[1]
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if c1 < tx || t2 <= c1 {
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return 0, 1
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}
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o := int(i)<<6 + int(c1)
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i = t.Index[o]
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c2 := s[2]
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if c2 < tx || t2 <= c2 {
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return 0, 2
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}
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o = int(i)<<6 + int(c2)
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i = t.Index[o]
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c3 := s[3]
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if c3 < tx || t2 <= c3 {
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return 0, 3
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}
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return t.lookupValue(i, c3), 4
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}
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// Illegal rune
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return 0, 1
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}
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// The body of lookupString is a verbatim copy of that of lookup.
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func (t *Trie) lookupString(s string) (v Elem, sz int) {
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c0 := s[0]
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switch {
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case c0 < tx:
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return Elem(t.Values0[c0]), 1
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case c0 < t2:
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return 0, 1
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case c0 < t3:
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if len(s) < 2 {
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return 0, 0
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}
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i := t.Index0[c0]
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c1 := s[1]
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if c1 < tx || t2 <= c1 {
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return 0, 1
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}
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return t.lookupValue(i, c1), 2
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case c0 < t4:
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if len(s) < 3 {
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return 0, 0
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}
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i := t.Index0[c0]
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c1 := s[1]
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if c1 < tx || t2 <= c1 {
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return 0, 1
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}
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o := int(i)<<6 + int(c1)
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i = t.Index[o]
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c2 := s[2]
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if c2 < tx || t2 <= c2 {
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return 0, 2
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}
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return t.lookupValue(i, c2), 3
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case c0 < t5:
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if len(s) < 4 {
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return 0, 0
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}
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i := t.Index0[c0]
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c1 := s[1]
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if c1 < tx || t2 <= c1 {
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return 0, 1
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}
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o := int(i)<<6 + int(c1)
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i = t.Index[o]
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c2 := s[2]
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if c2 < tx || t2 <= c2 {
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return 0, 2
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}
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o = int(i)<<6 + int(c2)
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i = t.Index[o]
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c3 := s[3]
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if c3 < tx || t2 <= c3 {
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return 0, 3
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}
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return t.lookupValue(i, c3), 4
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}
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// Illegal rune
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return 0, 1
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}
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