From ce933f77c865a15670855ac5941fe200752b739f Mon Sep 17 00:00:00 2001 From: Simon Sapin Date: Mon, 18 Mar 2019 20:16:37 +0100 Subject: [PATCH] Make u8::to_ascii_lowercase and to_ascii_uppercase branchless --- src/libcore/benches/ascii_case.rs | 22 +----- src/libcore/num/mod.rs | 122 ++++++++++-------------------- 2 files changed, 43 insertions(+), 101 deletions(-) diff --git a/src/libcore/benches/ascii_case.rs b/src/libcore/benches/ascii_case.rs index 43242ca3f364e..1c9691d1ee173 100644 --- a/src/libcore/benches/ascii_case.rs +++ b/src/libcore/benches/ascii_case.rs @@ -1,24 +1,4 @@ -// Lower-case ASCII 'a' is the first byte that has its highest bit set after wrap-adding 0x1F: -// -// b'a' + 0x1F == 0x80 == 0b1000_0000 -// b'z' + 0x1F == 0x98 == 0b10011000 -// -// Lower-case ASCII 'z' is the last byte that has its highest bit unset after wrap-adding 0x05: -// -// b'a' + 0x05 == 0x66 == 0b0110_0110 -// b'z' + 0x05 == 0x7F == 0b0111_1111 -// -// … except for 0xFB to 0xFF, but those are in the range of bytes that have the highest bit -// unset again after adding 0x1F. -// -// So `(byte + 0x1f) & !(byte + 5)` has its highest bit set -// iff `byte` is a lower-case ASCII letter. -// -// Lower-case ASCII letters all have the 0x20 bit set. -// (Two positions right of 0x80, the highest bit.) -// Unsetting that bit produces the same letter, in upper-case. -// -// Therefore: +// See comments in `u8::to_ascii_uppercase` in `src/libcore/num/mod.rs`. fn branchless_to_ascii_upper_case(byte: u8) -> u8 { byte & !( diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs index d93cfbc2a28ac..977e21e0dc89a 100644 --- a/src/libcore/num/mod.rs +++ b/src/libcore/num/mod.rs @@ -3794,7 +3794,39 @@ impl u8 { #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")] #[inline] pub fn to_ascii_uppercase(&self) -> u8 { - ASCII_UPPERCASE_MAP[*self as usize] + // See benchmarks in src/libcore/benches/ascii_case.rs + + // Lower-case ASCII 'a' is the first byte that has its highest bit set + // after wrap-adding 0x1F: + // + // b'a' + 0x1F == 0x80 == 0b1000_0000 + // b'z' + 0x1F == 0x98 == 0b10011000 + // + // Lower-case ASCII 'z' is the last byte that has its highest bit unset + // after wrap-adding 0x05: + // + // b'a' + 0x05 == 0x66 == 0b0110_0110 + // b'z' + 0x05 == 0x7F == 0b0111_1111 + // + // … except for 0xFB to 0xFF, but those are in the range of bytes + // that have the highest bit unset again after adding 0x1F. + // + // So `(byte + 0x1f) & !(byte + 5)` has its highest bit set + // iff `byte` is a lower-case ASCII letter. + // + // Lower-case ASCII letters all have the 0x20 bit set. + // (Two positions right of 0x80, the highest bit.) + // Unsetting that bit produces the same letter, in upper-case. + // + // Therefore: + *self & + !( + ( + self.wrapping_add(0x1f) & + !self.wrapping_add(0x05) & + 0x80 + ) >> 2 + ) } /// Makes a copy of the value in its ASCII lower case equivalent. @@ -3816,7 +3848,15 @@ impl u8 { #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")] #[inline] pub fn to_ascii_lowercase(&self) -> u8 { - ASCII_LOWERCASE_MAP[*self as usize] + // See comments in to_ascii_uppercase above. + *self | + ( + ( + self.wrapping_add(0x3f) & + !self.wrapping_add(0x25) & + 0x80 + ) >> 2 + ) } /// Checks that two values are an ASCII case-insensitive match. @@ -4940,84 +4980,6 @@ impl_from! { u32, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0" // Float -> Float impl_from! { f32, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")] } -static ASCII_LOWERCASE_MAP: [u8; 256] = [ - 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, - 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, - 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, - 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, - b' ', b'!', b'"', b'#', b'$', b'%', b'&', b'\'', - b'(', b')', b'*', b'+', b',', b'-', b'.', b'/', - b'0', b'1', b'2', b'3', b'4', b'5', b'6', b'7', - b'8', b'9', b':', b';', b'<', b'=', b'>', b'?', - b'@', - - b'a', b'b', b'c', b'd', b'e', b'f', b'g', - b'h', b'i', b'j', b'k', b'l', b'm', b'n', b'o', - b'p', b'q', b'r', b's', b't', b'u', b'v', b'w', - b'x', b'y', b'z', - - b'[', b'\\', b']', b'^', b'_', - b'`', b'a', b'b', b'c', b'd', b'e', b'f', b'g', - b'h', b'i', b'j', b'k', b'l', b'm', b'n', b'o', - b'p', b'q', b'r', b's', b't', b'u', b'v', b'w', - b'x', b'y', b'z', b'{', b'|', b'}', b'~', 0x7f, - 0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, - 0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f, - 0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, - 0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f, - 0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7, - 0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf, - 0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7, - 0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf, - 0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7, - 0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf, - 0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, - 0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf, - 0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, - 0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef, - 0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, - 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff, -]; - -static ASCII_UPPERCASE_MAP: [u8; 256] = [ - 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, - 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, - 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, - 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, - b' ', b'!', b'"', b'#', b'$', b'%', b'&', b'\'', - b'(', b')', b'*', b'+', b',', b'-', b'.', b'/', - b'0', b'1', b'2', b'3', b'4', b'5', b'6', b'7', - b'8', b'9', b':', b';', b'<', b'=', b'>', b'?', - b'@', b'A', b'B', b'C', b'D', b'E', b'F', b'G', - b'H', b'I', b'J', b'K', b'L', b'M', b'N', b'O', - b'P', b'Q', b'R', b'S', b'T', b'U', b'V', b'W', - b'X', b'Y', b'Z', b'[', b'\\', b']', b'^', b'_', - b'`', - - b'A', b'B', b'C', b'D', b'E', b'F', b'G', - b'H', b'I', b'J', b'K', b'L', b'M', b'N', b'O', - b'P', b'Q', b'R', b'S', b'T', b'U', b'V', b'W', - b'X', b'Y', b'Z', - - b'{', b'|', b'}', b'~', 0x7f, - 0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, - 0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f, - 0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, - 0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f, - 0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7, - 0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf, - 0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7, - 0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf, - 0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7, - 0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf, - 0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, - 0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf, - 0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, - 0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef, - 0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, - 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff, -]; - enum AsciiCharacterClass { C, // control Cw, // control whitespace