blob: 9380624fd9e556f989d82d6c265626206b5c8e20 [file] [log] [blame]
// Copyright 2009 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.
// This package provides data and functions to test some properties of Unicode code points.
package unicode
const (
MaxRune = 0x10FFFF // Maximum valid Unicode code point.
ReplacementChar = 0xFFFD // Represents invalid code points.
)
// The representation of a range of Unicode code points. The range runs from Lo to Hi
// inclusive and has the specified stride.
type Range struct {
Lo int
Hi int
Stride int
}
// CaseRange represents a range of Unicode code points for simple (one
// code point to one code point) case conversion.
// The range runs from Lo to Hi inclusive, with a fixed stride of 1. Deltas
// are the number to add to the code point to reach the code point for a
// different case for that character. They may be negative. If zero, it
// means the character is in the corresponding case. There is a special
// case representing sequences of alternating corresponding Upper and Lower
// pairs. It appears with a fixed Delta of
// {UpperLower, UpperLower, UpperLower}
// The constant UpperLower has an otherwise impossible delta value.
type CaseRange struct {
Lo int
Hi int
Delta d
}
// SpecialCase represents language-specific case mappings such as Turkish.
// Methods of SpecialCase customize (by overriding) the standard mappings.
type SpecialCase []CaseRange
//BUG(r): Provide a mechanism for full case folding (those that involve
// multiple runes in the input or output).
// Indices into the Delta arrays inside CaseRanges for case mapping.
const (
UpperCase = iota
LowerCase
TitleCase
MaxCase
)
type d [MaxCase]int32 // to make the CaseRanges text shorter
// If the Delta field of a CaseRange is UpperLower or LowerUpper, it means
// this CaseRange represents a sequence of the form (say)
// Upper Lower Upper Lower.
const (
UpperLower = MaxRune + 1 // (Cannot be a valid delta.)
)
// Is tests whether rune is in the specified table of ranges.
func Is(ranges []Range, rune int) bool {
// common case: rune is ASCII or Latin-1
if rune < 0x100 {
for _, r := range ranges {
if rune > r.Hi {
continue
}
if rune < r.Lo {
return false
}
return (rune-r.Lo)%r.Stride == 0
}
return false
}
// binary search over ranges
lo := 0
hi := len(ranges)
for lo < hi {
m := lo + (hi-lo)/2
r := ranges[m]
if r.Lo <= rune && rune <= r.Hi {
return (rune-r.Lo)%r.Stride == 0
}
if rune < r.Lo {
hi = m
} else {
lo = m + 1
}
}
return false
}
// IsUpper reports whether the rune is an upper case letter.
func IsUpper(rune int) bool {
if rune < 0x80 { // quick ASCII check
return 'A' <= rune && rune <= 'Z'
}
return Is(Upper, rune)
}
// IsLower reports whether the rune is a lower case letter.
func IsLower(rune int) bool {
if rune < 0x80 { // quick ASCII check
return 'a' <= rune && rune <= 'z'
}
return Is(Lower, rune)
}
// IsTitle reports whether the rune is a title case letter.
func IsTitle(rune int) bool {
if rune < 0x80 { // quick ASCII check
return false
}
return Is(Title, rune)
}
// IsLetter reports whether the rune is a letter.
func IsLetter(rune int) bool {
if rune < 0x80 { // quick ASCII check
rune &^= 'a' - 'A'
return 'A' <= rune && rune <= 'Z'
}
return Is(Letter, rune)
}
// IsSpace reports whether the rune is a white space character.
func IsSpace(rune int) bool {
if rune <= 0xFF { // quick Latin-1 check
switch rune {
case '\t', '\n', '\v', '\f', '\r', ' ', 0x85, 0xA0:
return true
}
return false
}
return Is(White_Space, rune)
}
// to maps the rune using the specified case mapping.
func to(_case int, rune int, caseRange []CaseRange) int {
if _case < 0 || MaxCase <= _case {
return ReplacementChar // as reasonable an error as any
}
// binary search over ranges
lo := 0
hi := len(caseRange)
for lo < hi {
m := lo + (hi-lo)/2
r := caseRange[m]
if r.Lo <= rune && rune <= r.Hi {
delta := int(r.Delta[_case])
if delta > MaxRune {
// In an Upper-Lower sequence, which always starts with
// an UpperCase letter, the real deltas always look like:
// {0, 1, 0} UpperCase (Lower is next)
// {-1, 0, -1} LowerCase (Upper, Title are previous)
// The characters at even offsets from the beginning of the
// sequence are upper case; the ones at odd offsets are lower.
// The correct mapping can be done by clearing or setting the low
// bit in the sequence offset.
// The constants UpperCase and TitleCase are even while LowerCase
// is odd so we take the low bit from _case.
return r.Lo + ((rune-r.Lo)&^1 | _case&1)
}
return rune + delta
}
if rune < r.Lo {
hi = m
} else {
lo = m + 1
}
}
return rune
}
// To maps the rune to the specified case: UpperCase, LowerCase, or TitleCase.
func To(_case int, rune int) int {
return to(_case, rune, CaseRanges)
}
// ToUpper maps the rune to upper case.
func ToUpper(rune int) int {
if rune < 0x80 { // quick ASCII check
if 'a' <= rune && rune <= 'z' {
rune -= 'a' - 'A'
}
return rune
}
return To(UpperCase, rune)
}
// ToLower maps the rune to lower case.
func ToLower(rune int) int {
if rune < 0x80 { // quick ASCII check
if 'A' <= rune && rune <= 'Z' {
rune += 'a' - 'A'
}
return rune
}
return To(LowerCase, rune)
}
// ToTitle maps the rune to title case.
func ToTitle(rune int) int {
if rune < 0x80 { // quick ASCII check
if 'a' <= rune && rune <= 'z' { // title case is upper case for ASCII
rune -= 'a' - 'A'
}
return rune
}
return To(TitleCase, rune)
}
// ToUpper maps the rune to upper case giving priority to the special mapping.
func (special SpecialCase) ToUpper(rune int) int {
r := to(UpperCase, rune, []CaseRange(special))
if r == rune {
r = ToUpper(rune)
}
return r
}
// ToTitle maps the rune to title case giving priority to the special mapping.
func (special SpecialCase) ToTitle(rune int) int {
r := to(TitleCase, rune, []CaseRange(special))
if r == rune {
r = ToTitle(rune)
}
return r
}
// ToLower maps the rune to lower case giving priority to the special mapping.
func (special SpecialCase) ToLower(rune int) int {
r := to(LowerCase, rune, []CaseRange(special))
if r == rune {
r = ToLower(rune)
}
return r
}