63 lines
1.5 KiB
Go
63 lines
1.5 KiB
Go
package misspell
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// ByteToUpper converts an ascii byte to upper cases
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// Uses a branchless algorithm
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func ByteToUpper(x byte) byte {
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b := byte(0x80) | x
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c := b - byte(0x61)
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d := ^(b - byte(0x7b))
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e := (c & d) & (^x & 0x7f)
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return x - (e >> 2)
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}
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// ByteToLower converts an ascii byte to lower case
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// uses a branchless algorithm
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func ByteToLower(eax byte) byte {
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ebx := eax&byte(0x7f) + byte(0x25)
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ebx = ebx&byte(0x7f) + byte(0x1a)
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ebx = ((ebx & ^eax) >> 2) & byte(0x20)
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return eax + ebx
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}
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// ByteEqualFold does ascii compare, case insensitive
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func ByteEqualFold(a, b byte) bool {
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return a == b || ByteToLower(a) == ByteToLower(b)
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}
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// StringEqualFold ASCII case-insensitive comparison
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// golang toUpper/toLower for both bytes and strings
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// appears to be Unicode based which is super slow
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// based from https://codereview.appspot.com/5180044/patch/14007/21002
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func StringEqualFold(s1, s2 string) bool {
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if len(s1) != len(s2) {
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return false
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}
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for i := 0; i < len(s1); i++ {
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c1 := s1[i]
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c2 := s2[i]
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// c1 & c2
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if c1 != c2 {
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c1 |= 'a' - 'A'
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c2 |= 'a' - 'A'
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if c1 != c2 || c1 < 'a' || c1 > 'z' {
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return false
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}
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}
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}
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return true
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}
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// StringHasPrefixFold is similar to strings.HasPrefix but comparison
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// is done ignoring ASCII case.
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// /
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func StringHasPrefixFold(s1, s2 string) bool {
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// prefix is bigger than input --> false
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if len(s1) < len(s2) {
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return false
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}
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if len(s1) == len(s2) {
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return StringEqualFold(s1, s2)
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}
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return StringEqualFold(s1[:len(s2)], s2)
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}
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