Source file src/unicode/letter.go

Documentation: unicode

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package unicode provides data and functions to test some properties of
     6  // Unicode code points.
     7  package unicode
     8  
     9  const (
    10  	MaxRune         = '\U0010FFFF' // Maximum valid Unicode code point.
    11  	ReplacementChar = '\uFFFD'     // Represents invalid code points.
    12  	MaxASCII        = '\u007F'     // maximum ASCII value.
    13  	MaxLatin1       = '\u00FF'     // maximum Latin-1 value.
    14  )
    15  
    16  // RangeTable defines a set of Unicode code points by listing the ranges of
    17  // code points within the set. The ranges are listed in two slices
    18  // to save space: a slice of 16-bit ranges and a slice of 32-bit ranges.
    19  // The two slices must be in sorted order and non-overlapping.
    20  // Also, R32 should contain only values >= 0x10000 (1<<16).
    21  type RangeTable struct {
    22  	R16         []Range16
    23  	R32         []Range32
    24  	LatinOffset int // number of entries in R16 with Hi <= MaxLatin1
    25  }
    26  
    27  // Range16 represents of a range of 16-bit Unicode code points. The range runs from Lo to Hi
    28  // inclusive and has the specified stride.
    29  type Range16 struct {
    30  	Lo     uint16
    31  	Hi     uint16
    32  	Stride uint16
    33  }
    34  
    35  // Range32 represents of a range of Unicode code points and is used when one or
    36  // more of the values will not fit in 16 bits. The range runs from Lo to Hi
    37  // inclusive and has the specified stride. Lo and Hi must always be >= 1<<16.
    38  type Range32 struct {
    39  	Lo     uint32
    40  	Hi     uint32
    41  	Stride uint32
    42  }
    43  
    44  // CaseRange represents a range of Unicode code points for simple (one
    45  // code point to one code point) case conversion.
    46  // The range runs from Lo to Hi inclusive, with a fixed stride of 1. Deltas
    47  // are the number to add to the code point to reach the code point for a
    48  // different case for that character. They may be negative. If zero, it
    49  // means the character is in the corresponding case. There is a special
    50  // case representing sequences of alternating corresponding Upper and Lower
    51  // pairs. It appears with a fixed Delta of
    52  //	{UpperLower, UpperLower, UpperLower}
    53  // The constant UpperLower has an otherwise impossible delta value.
    54  type CaseRange struct {
    55  	Lo    uint32
    56  	Hi    uint32
    57  	Delta d
    58  }
    59  
    60  // SpecialCase represents language-specific case mappings such as Turkish.
    61  // Methods of SpecialCase customize (by overriding) the standard mappings.
    62  type SpecialCase []CaseRange
    63  
    64  // BUG(r): There is no mechanism for full case folding, that is, for
    65  // characters that involve multiple runes in the input or output.
    66  
    67  // Indices into the Delta arrays inside CaseRanges for case mapping.
    68  const (
    69  	UpperCase = iota
    70  	LowerCase
    71  	TitleCase
    72  	MaxCase
    73  )
    74  
    75  type d [MaxCase]rune // to make the CaseRanges text shorter
    76  
    77  // If the Delta field of a CaseRange is UpperLower, it means
    78  // this CaseRange represents a sequence of the form (say)
    79  // Upper Lower Upper Lower.
    80  const (
    81  	UpperLower = MaxRune + 1 // (Cannot be a valid delta.)
    82  )
    83  
    84  // linearMax is the maximum size table for linear search for non-Latin1 rune.
    85  // Derived by running 'go test -calibrate'.
    86  const linearMax = 18
    87  
    88  // is16 reports whether r is in the sorted slice of 16-bit ranges.
    89  func is16(ranges []Range16, r uint16) bool {
    90  	if len(ranges) <= linearMax || r <= MaxLatin1 {
    91  		for i := range ranges {
    92  			range_ := &ranges[i]
    93  			if r < range_.Lo {
    94  				return false
    95  			}
    96  			if r <= range_.Hi {
    97  				return range_.Stride == 1 || (r-range_.Lo)%range_.Stride == 0
    98  			}
    99  		}
   100  		return false
   101  	}
   102  
   103  	// binary search over ranges
   104  	lo := 0
   105  	hi := len(ranges)
   106  	for lo < hi {
   107  		m := lo + (hi-lo)/2
   108  		range_ := &ranges[m]
   109  		if range_.Lo <= r && r <= range_.Hi {
   110  			return range_.Stride == 1 || (r-range_.Lo)%range_.Stride == 0
   111  		}
   112  		if r < range_.Lo {
   113  			hi = m
   114  		} else {
   115  			lo = m + 1
   116  		}
   117  	}
   118  	return false
   119  }
   120  
   121  // is32 reports whether r is in the sorted slice of 32-bit ranges.
   122  func is32(ranges []Range32, r uint32) bool {
   123  	if len(ranges) <= linearMax {
   124  		for i := range ranges {
   125  			range_ := &ranges[i]
   126  			if r < range_.Lo {
   127  				return false
   128  			}
   129  			if r <= range_.Hi {
   130  				return range_.Stride == 1 || (r-range_.Lo)%range_.Stride == 0
   131  			}
   132  		}
   133  		return false
   134  	}
   135  
   136  	// binary search over ranges
   137  	lo := 0
   138  	hi := len(ranges)
   139  	for lo < hi {
   140  		m := lo + (hi-lo)/2
   141  		range_ := ranges[m]
   142  		if range_.Lo <= r && r <= range_.Hi {
   143  			return range_.Stride == 1 || (r-range_.Lo)%range_.Stride == 0
   144  		}
   145  		if r < range_.Lo {
   146  			hi = m
   147  		} else {
   148  			lo = m + 1
   149  		}
   150  	}
   151  	return false
   152  }
   153  
   154  // Is reports whether the rune is in the specified table of ranges.
   155  func Is(rangeTab *RangeTable, r rune) bool {
   156  	r16 := rangeTab.R16
   157  	if len(r16) > 0 && r <= rune(r16[len(r16)-1].Hi) {
   158  		return is16(r16, uint16(r))
   159  	}
   160  	r32 := rangeTab.R32
   161  	if len(r32) > 0 && r >= rune(r32[0].Lo) {
   162  		return is32(r32, uint32(r))
   163  	}
   164  	return false
   165  }
   166  
   167  func isExcludingLatin(rangeTab *RangeTable, r rune) bool {
   168  	r16 := rangeTab.R16
   169  	if off := rangeTab.LatinOffset; len(r16) > off && r <= rune(r16[len(r16)-1].Hi) {
   170  		return is16(r16[off:], uint16(r))
   171  	}
   172  	r32 := rangeTab.R32
   173  	if len(r32) > 0 && r >= rune(r32[0].Lo) {
   174  		return is32(r32, uint32(r))
   175  	}
   176  	return false
   177  }
   178  
   179  // IsUpper reports whether the rune is an upper case letter.
   180  func IsUpper(r rune) bool {
   181  	// See comment in IsGraphic.
   182  	if uint32(r) <= MaxLatin1 {
   183  		return properties[uint8(r)]&pLmask == pLu
   184  	}
   185  	return isExcludingLatin(Upper, r)
   186  }
   187  
   188  // IsLower reports whether the rune is a lower case letter.
   189  func IsLower(r rune) bool {
   190  	// See comment in IsGraphic.
   191  	if uint32(r) <= MaxLatin1 {
   192  		return properties[uint8(r)]&pLmask == pLl
   193  	}
   194  	return isExcludingLatin(Lower, r)
   195  }
   196  
   197  // IsTitle reports whether the rune is a title case letter.
   198  func IsTitle(r rune) bool {
   199  	if r <= MaxLatin1 {
   200  		return false
   201  	}
   202  	return isExcludingLatin(Title, r)
   203  }
   204  
   205  // to maps the rune using the specified case mapping.
   206  // It additionally reports whether caseRange contained a mapping for r.
   207  func to(_case int, r rune, caseRange []CaseRange) (mappedRune rune, foundMapping bool) {
   208  	if _case < 0 || MaxCase <= _case {
   209  		return ReplacementChar, false // as reasonable an error as any
   210  	}
   211  	// binary search over ranges
   212  	lo := 0
   213  	hi := len(caseRange)
   214  	for lo < hi {
   215  		m := lo + (hi-lo)/2
   216  		cr := caseRange[m]
   217  		if rune(cr.Lo) <= r && r <= rune(cr.Hi) {
   218  			delta := cr.Delta[_case]
   219  			if delta > MaxRune {
   220  				// In an Upper-Lower sequence, which always starts with
   221  				// an UpperCase letter, the real deltas always look like:
   222  				//	{0, 1, 0}    UpperCase (Lower is next)
   223  				//	{-1, 0, -1}  LowerCase (Upper, Title are previous)
   224  				// The characters at even offsets from the beginning of the
   225  				// sequence are upper case; the ones at odd offsets are lower.
   226  				// The correct mapping can be done by clearing or setting the low
   227  				// bit in the sequence offset.
   228  				// The constants UpperCase and TitleCase are even while LowerCase
   229  				// is odd so we take the low bit from _case.
   230  				return rune(cr.Lo) + ((r-rune(cr.Lo))&^1 | rune(_case&1)), true
   231  			}
   232  			return r + delta, true
   233  		}
   234  		if r < rune(cr.Lo) {
   235  			hi = m
   236  		} else {
   237  			lo = m + 1
   238  		}
   239  	}
   240  	return r, false
   241  }
   242  
   243  // To maps the rune to the specified case: UpperCase, LowerCase, or TitleCase.
   244  func To(_case int, r rune) rune {
   245  	r, _ = to(_case, r, CaseRanges)
   246  	return r
   247  }
   248  
   249  // ToUpper maps the rune to upper case.
   250  func ToUpper(r rune) rune {
   251  	if r <= MaxASCII {
   252  		if 'a' <= r && r <= 'z' {
   253  			r -= 'a' - 'A'
   254  		}
   255  		return r
   256  	}
   257  	return To(UpperCase, r)
   258  }
   259  
   260  // ToLower maps the rune to lower case.
   261  func ToLower(r rune) rune {
   262  	if r <= MaxASCII {
   263  		if 'A' <= r && r <= 'Z' {
   264  			r += 'a' - 'A'
   265  		}
   266  		return r
   267  	}
   268  	return To(LowerCase, r)
   269  }
   270  
   271  // ToTitle maps the rune to title case.
   272  func ToTitle(r rune) rune {
   273  	if r <= MaxASCII {
   274  		if 'a' <= r && r <= 'z' { // title case is upper case for ASCII
   275  			r -= 'a' - 'A'
   276  		}
   277  		return r
   278  	}
   279  	return To(TitleCase, r)
   280  }
   281  
   282  // ToUpper maps the rune to upper case giving priority to the special mapping.
   283  func (special SpecialCase) ToUpper(r rune) rune {
   284  	r1, hadMapping := to(UpperCase, r, []CaseRange(special))
   285  	if r1 == r && !hadMapping {
   286  		r1 = ToUpper(r)
   287  	}
   288  	return r1
   289  }
   290  
   291  // ToTitle maps the rune to title case giving priority to the special mapping.
   292  func (special SpecialCase) ToTitle(r rune) rune {
   293  	r1, hadMapping := to(TitleCase, r, []CaseRange(special))
   294  	if r1 == r && !hadMapping {
   295  		r1 = ToTitle(r)
   296  	}
   297  	return r1
   298  }
   299  
   300  // ToLower maps the rune to lower case giving priority to the special mapping.
   301  func (special SpecialCase) ToLower(r rune) rune {
   302  	r1, hadMapping := to(LowerCase, r, []CaseRange(special))
   303  	if r1 == r && !hadMapping {
   304  		r1 = ToLower(r)
   305  	}
   306  	return r1
   307  }
   308  
   309  // caseOrbit is defined in tables.go as []foldPair. Right now all the
   310  // entries fit in uint16, so use uint16. If that changes, compilation
   311  // will fail (the constants in the composite literal will not fit in uint16)
   312  // and the types here can change to uint32.
   313  type foldPair struct {
   314  	From uint16
   315  	To   uint16
   316  }
   317  
   318  // SimpleFold iterates over Unicode code points equivalent under
   319  // the Unicode-defined simple case folding. Among the code points
   320  // equivalent to rune (including rune itself), SimpleFold returns the
   321  // smallest rune > r if one exists, or else the smallest rune >= 0.
   322  // If r is not a valid Unicode code point, SimpleFold(r) returns r.
   323  //
   324  // For example:
   325  //	SimpleFold('A') = 'a'
   326  //	SimpleFold('a') = 'A'
   327  //
   328  //	SimpleFold('K') = 'k'
   329  //	SimpleFold('k') = '\u212A' (Kelvin symbol, K)
   330  //	SimpleFold('\u212A') = 'K'
   331  //
   332  //	SimpleFold('1') = '1'
   333  //
   334  //	SimpleFold(-2) = -2
   335  //
   336  func SimpleFold(r rune) rune {
   337  	if r < 0 || r > MaxRune {
   338  		return r
   339  	}
   340  
   341  	if int(r) < len(asciiFold) {
   342  		return rune(asciiFold[r])
   343  	}
   344  
   345  	// Consult caseOrbit table for special cases.
   346  	lo := 0
   347  	hi := len(caseOrbit)
   348  	for lo < hi {
   349  		m := lo + (hi-lo)/2
   350  		if rune(caseOrbit[m].From) < r {
   351  			lo = m + 1
   352  		} else {
   353  			hi = m
   354  		}
   355  	}
   356  	if lo < len(caseOrbit) && rune(caseOrbit[lo].From) == r {
   357  		return rune(caseOrbit[lo].To)
   358  	}
   359  
   360  	// No folding specified. This is a one- or two-element
   361  	// equivalence class containing rune and ToLower(rune)
   362  	// and ToUpper(rune) if they are different from rune.
   363  	if l := ToLower(r); l != r {
   364  		return l
   365  	}
   366  	return ToUpper(r)
   367  }
   368  

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