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case.go
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case.go
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package stringutils
import (
"unicode"
"unicode/utf8"
)
// based on strings.Map
// Map returns a copy of the string s with all its characters modified
// according to the mapping function. If mapping returns a negative value, the character is
// dropped from the string with no replacement.
func (sb *Builder) Map(mapping func(rune) rune, s string) {
// In the worst case, the string can grow when mapped, making
// things unpleasant. But it's so rare we barge in assuming it's
// fine. It could also shrink but that falls out naturally.
// The output buffer b is initialized on demand, the first
// time a character differs.
updated := false
sb.Grow(sb.Len() + len(s) + utf8.UTFMax)
for i, c := range s {
r := mapping(c)
if r == c && c != utf8.RuneError {
continue
}
var width int
if c == utf8.RuneError {
c, width = utf8.DecodeRuneInString(s[i:])
if width != 1 && r == c {
continue
}
} else {
width = utf8.RuneLen(c)
}
updated = true
sb.WriteString(s[:i])
if r >= 0 {
sb.WriteRune(r)
}
s = s[i+width:]
break
}
// Fast path for unchanged input
if updated { // didn't call b.Grow above
for _, c := range s {
r := mapping(c)
if r >= 0 {
// common case
// Due to inlining, it is more performant to determine if WriteByte should be
// invoked rather than always call WriteRune
if r < utf8.RuneSelf {
sb.WriteByte(byte(r))
} else {
// r is not a ASCII rune.
sb.WriteRune(r)
}
}
}
} else {
sb.WriteString(s)
}
}
// based on strings.ToUpper
// ToUpper returns s with all Unicode letters mapped to their upper case.
func (sb *Builder) WriteStringUpper(s string) {
isASCII, hasLower := true, false
for i := 0; i < len(s); i++ {
c := s[i]
if c >= utf8.RuneSelf {
isASCII = false
break
}
hasLower = hasLower || ('a' <= c && c <= 'z')
}
if isASCII { // optimize for ASCII-only strings.
if hasLower {
sb.Grow(sb.Len() + len(s))
for i := 0; i < len(s); i++ {
c := s[i]
if 'a' <= c && c <= 'z' {
c -= 'a' - 'A'
}
sb.WriteByte(c)
}
} else {
sb.WriteString(s)
}
} else {
sb.Map(unicode.ToUpper, s)
}
}
// based on strings.ToLower
// ToLower returns s with all Unicode letters mapped to their lower case.
func (sb *Builder) WriteStringLower(s string) {
isASCII, hasUpper := true, false
for i := 0; i < len(s); i++ {
c := s[i]
if c >= utf8.RuneSelf {
isASCII = false
break
}
hasUpper = hasUpper || ('A' <= c && c <= 'Z')
}
if isASCII { // optimize for ASCII-only strings.
if !hasUpper {
sb.WriteString(s)
return
}
sb.Grow(sb.Len() + len(s))
for i := 0; i < len(s); i++ {
c := s[i]
if 'A' <= c && c <= 'Z' {
c += 'a' - 'A'
}
sb.WriteByte(c)
}
} else {
sb.Map(unicode.ToLower, s)
}
}
const (
toLowerTable = "\x00\x01\x02\x03\x04\x05\x06\a\b\t\n\v\f\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !\"#$%&'()*+,-./0123456789:;<=>?@abcdefghijklmnopqrstuvwxyz[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\u007f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff"
toUpperTable = "\x00\x01\x02\x03\x04\x05\x06\a\b\t\n\v\f\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`ABCDEFGHIJKLMNOPQRSTUVWXYZ{|}~\u007f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff"
)
// ToLower converts ascii string to lower-case
func ToLower(b string) string {
res := make([]byte, len(b))
copy(res, b)
for i := 0; i < len(res); i++ {
res[i] = toLowerTable[res[i]]
}
return UnsafeString(res)
}
// ToUpper converts ascii string to upper-case
func ToUpper(b string) string {
res := make([]byte, len(b))
copy(res, b)
for i := 0; i < len(res); i++ {
res[i] = toUpperTable[res[i]]
}
return UnsafeString(res)
}
// EqualFold tests ascii strings for equality case-insensitively
func EqualFold(b, s string) bool {
if len(b) != len(s) {
return false
}
for i := len(b) - 1; i >= 0; i-- {
if toUpperTable[b[i]] != toUpperTable[s[i]] {
return false
}
}
return true
}