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