Make u8::to_ascii_lowercase and to_ascii_uppercase branchless
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Simon Sapin
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8740d5d171
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2 changed files with 43 additions and 101 deletions
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@ -1,24 +1,4 @@
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// Lower-case ASCII 'a' is the first byte that has its highest bit set after wrap-adding 0x1F:
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// See comments in `u8::to_ascii_uppercase` in `src/libcore/num/mod.rs`.
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//
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// b'a' + 0x1F == 0x80 == 0b1000_0000
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// b'z' + 0x1F == 0x98 == 0b10011000
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//
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// Lower-case ASCII 'z' is the last byte that has its highest bit unset after wrap-adding 0x05:
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//
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// b'a' + 0x05 == 0x66 == 0b0110_0110
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// b'z' + 0x05 == 0x7F == 0b0111_1111
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//
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// … except for 0xFB to 0xFF, but those are in the range of bytes that have the highest bit
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// unset again after adding 0x1F.
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//
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// So `(byte + 0x1f) & !(byte + 5)` has its highest bit set
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// iff `byte` is a lower-case ASCII letter.
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//
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// Lower-case ASCII letters all have the 0x20 bit set.
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// (Two positions right of 0x80, the highest bit.)
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// Unsetting that bit produces the same letter, in upper-case.
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//
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// Therefore:
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fn branchless_to_ascii_upper_case(byte: u8) -> u8 {
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fn branchless_to_ascii_upper_case(byte: u8) -> u8 {
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byte &
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byte &
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!(
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!(
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@ -3794,7 +3794,39 @@ impl u8 {
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#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
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#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
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#[inline]
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#[inline]
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pub fn to_ascii_uppercase(&self) -> u8 {
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pub fn to_ascii_uppercase(&self) -> u8 {
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ASCII_UPPERCASE_MAP[*self as usize]
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// See benchmarks in src/libcore/benches/ascii_case.rs
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// Lower-case ASCII 'a' is the first byte that has its highest bit set
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// after wrap-adding 0x1F:
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//
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// b'a' + 0x1F == 0x80 == 0b1000_0000
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// b'z' + 0x1F == 0x98 == 0b10011000
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//
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// Lower-case ASCII 'z' is the last byte that has its highest bit unset
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// after wrap-adding 0x05:
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//
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// b'a' + 0x05 == 0x66 == 0b0110_0110
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// b'z' + 0x05 == 0x7F == 0b0111_1111
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//
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// … except for 0xFB to 0xFF, but those are in the range of bytes
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// that have the highest bit unset again after adding 0x1F.
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//
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// So `(byte + 0x1f) & !(byte + 5)` has its highest bit set
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// iff `byte` is a lower-case ASCII letter.
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//
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// Lower-case ASCII letters all have the 0x20 bit set.
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// (Two positions right of 0x80, the highest bit.)
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// Unsetting that bit produces the same letter, in upper-case.
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//
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// Therefore:
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*self &
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!(
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(
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self.wrapping_add(0x1f) &
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!self.wrapping_add(0x05) &
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0x80
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) >> 2
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)
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}
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}
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/// Makes a copy of the value in its ASCII lower case equivalent.
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/// Makes a copy of the value in its ASCII lower case equivalent.
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@ -3816,7 +3848,15 @@ impl u8 {
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#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
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#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
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#[inline]
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#[inline]
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pub fn to_ascii_lowercase(&self) -> u8 {
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pub fn to_ascii_lowercase(&self) -> u8 {
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ASCII_LOWERCASE_MAP[*self as usize]
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// See comments in to_ascii_uppercase above.
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*self |
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(
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(
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self.wrapping_add(0x3f) &
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!self.wrapping_add(0x25) &
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0x80
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) >> 2
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)
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}
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}
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/// Checks that two values are an ASCII case-insensitive match.
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/// Checks that two values are an ASCII case-insensitive match.
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@ -4940,84 +4980,6 @@ impl_from! { u32, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0"
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// Float -> Float
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// Float -> Float
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impl_from! { f32, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
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impl_from! { f32, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
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static ASCII_LOWERCASE_MAP: [u8; 256] = [
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0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
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0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
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0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
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0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
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b' ', b'!', b'"', b'#', b'$', b'%', b'&', b'\'',
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b'(', b')', b'*', b'+', b',', b'-', b'.', b'/',
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b'0', b'1', b'2', b'3', b'4', b'5', b'6', b'7',
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b'8', b'9', b':', b';', b'<', b'=', b'>', b'?',
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b'@',
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b'a', b'b', b'c', b'd', b'e', b'f', b'g',
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b'h', b'i', b'j', b'k', b'l', b'm', b'n', b'o',
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b'p', b'q', b'r', b's', b't', b'u', b'v', b'w',
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b'x', b'y', b'z',
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b'[', b'\\', b']', b'^', b'_',
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b'`', b'a', b'b', b'c', b'd', b'e', b'f', b'g',
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b'h', b'i', b'j', b'k', b'l', b'm', b'n', b'o',
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b'p', b'q', b'r', b's', b't', b'u', b'v', b'w',
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b'x', b'y', b'z', b'{', b'|', b'}', b'~', 0x7f,
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0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
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0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
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0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
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0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
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0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
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0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
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0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
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0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
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0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
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0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
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0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
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0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
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0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
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0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
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0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
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0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
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];
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static ASCII_UPPERCASE_MAP: [u8; 256] = [
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0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
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0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
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0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
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0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
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b' ', b'!', b'"', b'#', b'$', b'%', b'&', b'\'',
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b'(', b')', b'*', b'+', b',', b'-', b'.', b'/',
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b'0', b'1', b'2', b'3', b'4', b'5', b'6', b'7',
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b'8', b'9', b':', b';', b'<', b'=', b'>', b'?',
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b'@', b'A', b'B', b'C', b'D', b'E', b'F', b'G',
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b'H', b'I', b'J', b'K', b'L', b'M', b'N', b'O',
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b'P', b'Q', b'R', b'S', b'T', b'U', b'V', b'W',
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b'X', b'Y', b'Z', b'[', b'\\', b']', b'^', b'_',
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b'`',
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b'A', b'B', b'C', b'D', b'E', b'F', b'G',
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b'H', b'I', b'J', b'K', b'L', b'M', b'N', b'O',
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b'P', b'Q', b'R', b'S', b'T', b'U', b'V', b'W',
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b'X', b'Y', b'Z',
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b'{', b'|', b'}', b'~', 0x7f,
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0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
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0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
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0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
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0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
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0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
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0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
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0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
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0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
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0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
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0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
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0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
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0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
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0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
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0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
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0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
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0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
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];
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enum AsciiCharacterClass {
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enum AsciiCharacterClass {
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C, // control
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C, // control
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Cw, // control whitespace
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Cw, // control whitespace
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