1 files changed, 371 insertions, 0 deletions
diff --git a/src/unicode/letter.go b/src/unicode/letter.go
new file mode 100644
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--- /dev/null
+++ b/src/unicode/letter.go
@@ -0,0 +1,371 @@
+// 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.
+
+// Package unicode provides data and functions to test some properties of
+// Unicode code points.
+package unicode
+
+const (
+	MaxRune         = '\U0010FFFF' // Maximum valid Unicode code point.
+	ReplacementChar = '\uFFFD'     // Represents invalid code points.
+	MaxASCII        = '\u007F'     // maximum ASCII value.
+	MaxLatin1       = '\u00FF'     // maximum Latin-1 value.
+)
+
+// RangeTable defines a set of Unicode code points by listing the ranges of
+// code points within the set. The ranges are listed in two slices
+// to save space: a slice of 16-bit ranges and a slice of 32-bit ranges.
+// The two slices must be in sorted order and non-overlapping.
+// Also, R32 should contain only values >= 0x10000 (1<<16).
+type RangeTable struct {
+	R16         []Range16
+	R32         []Range32
+	LatinOffset int // number of entries in R16 with Hi <= MaxLatin1
+}
+
+// Range16 represents of a range of 16-bit Unicode code points. The range runs from Lo to Hi
+// inclusive and has the specified stride.
+type Range16 struct {
+	Lo     uint16
+	Hi     uint16
+	Stride uint16
+}
+
+// Range32 represents of a range of Unicode code points and is used when one or
+// more of the values will not fit in 16 bits. The range runs from Lo to Hi
+// inclusive and has the specified stride. Lo and Hi must always be >= 1<<16.
+type Range32 struct {
+	Lo     uint32
+	Hi     uint32
+	Stride uint32
+}
+
+// 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    uint32
+	Hi    uint32
+	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): There is no mechanism for full case folding, that is, for
+// characters 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]rune // to make the CaseRanges text shorter
+
+// If the Delta field of a CaseRange is UpperLower, it means
+// this CaseRange represents a sequence of the form (say)
+// Upper Lower Upper Lower.
+const (
+	UpperLower = MaxRune + 1 // (Cannot be a valid delta.)
+)
+
+// linearMax is the maximum size table for linear search for non-Latin1 rune.
+// Derived by running 'go test -calibrate'.
+const linearMax = 18
+
+// is16 reports whether r is in the sorted slice of 16-bit ranges.
+func is16(ranges []Range16, r uint16) bool {
+	if len(ranges) <= linearMax || r <= MaxLatin1 {
+		for i := range ranges {
+			range_ := &ranges[i]
+			if r < range_.Lo {
+				return false
+			}
+			if r <= range_.Hi {
+				return range_.Stride == 1 || (r-range_.Lo)%range_.Stride == 0
+			}
+		}
+		return false
+	}
+
+	// binary search over ranges
+	lo := 0
+	hi := len(ranges)
+	for lo < hi {
+		m := lo + (hi-lo)/2
+		range_ := &ranges[m]
+		if range_.Lo <= r && r <= range_.Hi {
+			return range_.Stride == 1 || (r-range_.Lo)%range_.Stride == 0
+		}
+		if r < range_.Lo {
+			hi = m
+		} else {
+			lo = m + 1
+		}
+	}
+	return false
+}
+
+// is32 reports whether r is in the sorted slice of 32-bit ranges.
+func is32(ranges []Range32, r uint32) bool {
+	if len(ranges) <= linearMax {
+		for i := range ranges {
+			range_ := &ranges[i]
+			if r < range_.Lo {
+				return false
+			}
+			if r <= range_.Hi {
+				return range_.Stride == 1 || (r-range_.Lo)%range_.Stride == 0
+			}
+		}
+		return false
+	}
+
+	// binary search over ranges
+	lo := 0
+	hi := len(ranges)
+	for lo < hi {
+		m := lo + (hi-lo)/2
+		range_ := ranges[m]
+		if range_.Lo <= r && r <= range_.Hi {
+			return range_.Stride == 1 || (r-range_.Lo)%range_.Stride == 0
+		}
+		if r < range_.Lo {
+			hi = m
+		} else {
+			lo = m + 1
+		}
+	}
+	return false
+}
+
+// Is reports whether the rune is in the specified table of ranges.
+func Is(rangeTab *RangeTable, r rune) bool {
+	r16 := rangeTab.R16
+	// Compare as uint32 to correctly handle negative runes.
+	if len(r16) > 0 && uint32(r) <= uint32(r16[len(r16)-1].Hi) {
+		return is16(r16, uint16(r))
+	}
+	r32 := rangeTab.R32
+	if len(r32) > 0 && r >= rune(r32[0].Lo) {
+		return is32(r32, uint32(r))
+	}
+	return false
+}
+
+func isExcludingLatin(rangeTab *RangeTable, r rune) bool {
+	r16 := rangeTab.R16
+	// Compare as uint32 to correctly handle negative runes.
+	if off := rangeTab.LatinOffset; len(r16) > off && uint32(r) <= uint32(r16[len(r16)-1].Hi) {
+		return is16(r16[off:], uint16(r))
+	}
+	r32 := rangeTab.R32
+	if len(r32) > 0 && r >= rune(r32[0].Lo) {
+		return is32(r32, uint32(r))
+	}
+	return false
+}
+
+// IsUpper reports whether the rune is an upper case letter.
+func IsUpper(r rune) bool {
+	// See comment in IsGraphic.
+	if uint32(r) <= MaxLatin1 {
+		return properties[uint8(r)]&pLmask == pLu
+	}
+	return isExcludingLatin(Upper, r)
+}
+
+// IsLower reports whether the rune is a lower case letter.
+func IsLower(r rune) bool {
+	// See comment in IsGraphic.
+	if uint32(r) <= MaxLatin1 {
+		return properties[uint8(r)]&pLmask == pLl
+	}
+	return isExcludingLatin(Lower, r)
+}
+
+// IsTitle reports whether the rune is a title case letter.
+func IsTitle(r rune) bool {
+	if r <= MaxLatin1 {
+		return false
+	}
+	return isExcludingLatin(Title, r)
+}
+
+// to maps the rune using the specified case mapping.
+// It additionally reports whether caseRange contained a mapping for r.
+func to(_case int, r rune, caseRange []CaseRange) (mappedRune rune, foundMapping bool) {
+	if _case < 0 || MaxCase <= _case {
+		return ReplacementChar, false // as reasonable an error as any
+	}
+	// binary search over ranges
+	lo := 0
+	hi := len(caseRange)
+	for lo < hi {
+		m := lo + (hi-lo)/2
+		cr := caseRange[m]
+		if rune(cr.Lo) <= r && r <= rune(cr.Hi) {
+			delta := cr.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 rune(cr.Lo) + ((r-rune(cr.Lo))&^1 | rune(_case&1)), true
+			}
+			return r + delta, true
+		}
+		if r < rune(cr.Lo) {
+			hi = m
+		} else {
+			lo = m + 1
+		}
+	}
+	return r, false
+}
+
+// To maps the rune to the specified case: UpperCase, LowerCase, or TitleCase.
+func To(_case int, r rune) rune {
+	r, _ = to(_case, r, CaseRanges)
+	return r
+}
+
+// ToUpper maps the rune to upper case.
+func ToUpper(r rune) rune {
+	if r <= MaxASCII {
+		if 'a' <= r && r <= 'z' {
+			r -= 'a' - 'A'
+		}
+		return r
+	}
+	return To(UpperCase, r)
+}
+
+// ToLower maps the rune to lower case.
+func ToLower(r rune) rune {
+	if r <= MaxASCII {
+		if 'A' <= r && r <= 'Z' {
+			r += 'a' - 'A'
+		}
+		return r
+	}
+	return To(LowerCase, r)
+}
+
+// ToTitle maps the rune to title case.
+func ToTitle(r rune) rune {
+	if r <= MaxASCII {
+		if 'a' <= r && r <= 'z' { // title case is upper case for ASCII
+			r -= 'a' - 'A'
+		}
+		return r
+	}
+	return To(TitleCase, r)
+}
+
+// ToUpper maps the rune to upper case giving priority to the special mapping.
+func (special SpecialCase) ToUpper(r rune) rune {
+	r1, hadMapping := to(UpperCase, r, []CaseRange(special))
+	if r1 == r && !hadMapping {
+		r1 = ToUpper(r)
+	}
+	return r1
+}
+
+// ToTitle maps the rune to title case giving priority to the special mapping.
+func (special SpecialCase) ToTitle(r rune) rune {
+	r1, hadMapping := to(TitleCase, r, []CaseRange(special))
+	if r1 == r && !hadMapping {
+		r1 = ToTitle(r)
+	}
+	return r1
+}
+
+// ToLower maps the rune to lower case giving priority to the special mapping.
+func (special SpecialCase) ToLower(r rune) rune {
+	r1, hadMapping := to(LowerCase, r, []CaseRange(special))
+	if r1 == r && !hadMapping {
+		r1 = ToLower(r)
+	}
+	return r1
+}
+
+// caseOrbit is defined in tables.go as []foldPair. Right now all the
+// entries fit in uint16, so use uint16. If that changes, compilation
+// will fail (the constants in the composite literal will not fit in uint16)
+// and the types here can change to uint32.
+type foldPair struct {
+	From uint16
+	To   uint16
+}
+
+// SimpleFold iterates over Unicode code points equivalent under
+// the Unicode-defined simple case folding. Among the code points
+// equivalent to rune (including rune itself), SimpleFold returns the
+// smallest rune > r if one exists, or else the smallest rune >= 0.
+// If r is not a valid Unicode code point, SimpleFold(r) returns r.
+//
+// For example:
+//
+//	SimpleFold('A') = 'a'
+//	SimpleFold('a') = 'A'
+//
+//	SimpleFold('K') = 'k'
+//	SimpleFold('k') = '\u212A' (Kelvin symbol, K)
+//	SimpleFold('\u212A') = 'K'
+//
+//	SimpleFold('1') = '1'
+//
+//	SimpleFold(-2) = -2
+func SimpleFold(r rune) rune {
+	if r < 0 || r > MaxRune {
+		return r
+	}
+
+	if int(r) < len(asciiFold) {
+		return rune(asciiFold[r])
+	}
+
+	// Consult caseOrbit table for special cases.
+	lo := 0
+	hi := len(caseOrbit)
+	for lo < hi {
+		m := lo + (hi-lo)/2
+		if rune(caseOrbit[m].From) < r {
+			lo = m + 1
+		} else {
+			hi = m
+		}
+	}
+	if lo < len(caseOrbit) && rune(caseOrbit[lo].From) == r {
+		return rune(caseOrbit[lo].To)
+	}
+
+	// No folding specified. This is a one- or two-element
+	// equivalence class containing rune and ToLower(rune)
+	// and ToUpper(rune) if they are different from rune.
+	if l := ToLower(r); l != r {
+		return l
+	}
+	return ToUpper(r)
+}