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352 lines
11 KiB
Rust
352 lines
11 KiB
Rust
mod is_ascii;
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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 == 0b1001_1000
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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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fn branchless_to_ascii_upper_case(byte: u8) -> u8 {
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byte & !((byte.wrapping_add(0x1f) & !byte.wrapping_add(0x05) & 0x80) >> 2)
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}
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macro_rules! benches {
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($( fn $name: ident($arg: ident: &mut [u8]) $body: block )+ @iter $( $is_: ident, )+) => {
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benches! {@
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$( fn $name($arg: &mut [u8]) $body )+
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$( fn $is_(bytes: &mut [u8]) { bytes.iter().all(u8::$is_) } )+
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}
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};
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(@$( fn $name: ident($arg: ident: &mut [u8]) $body: block )+) => {
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benches!(mod short SHORT $($name $arg $body)+);
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benches!(mod medium MEDIUM $($name $arg $body)+);
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benches!(mod long LONG $($name $arg $body)+);
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};
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(mod $mod_name: ident $input: ident $($name: ident $arg: ident $body: block)+) => {
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mod $mod_name {
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use super::*;
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$(
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#[bench]
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fn $name(bencher: &mut Bencher) {
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bencher.bytes = $input.len() as u64;
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bencher.iter(|| {
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let mut vec = $input.as_bytes().to_vec();
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{
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let $arg = &mut vec[..];
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black_box($body);
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}
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vec
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})
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}
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)+
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}
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}
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}
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use test::black_box;
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use test::Bencher;
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benches! {
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fn case00_alloc_only(_bytes: &mut [u8]) {}
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fn case01_black_box_read_each_byte(bytes: &mut [u8]) {
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for byte in bytes {
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black_box(*byte);
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}
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}
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fn case02_lookup_table(bytes: &mut [u8]) {
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for byte in bytes {
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*byte = ASCII_UPPERCASE_MAP[*byte as usize]
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}
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}
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fn case03_branch_and_subtract(bytes: &mut [u8]) {
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for byte in bytes {
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*byte = if b'a' <= *byte && *byte <= b'z' {
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*byte - b'a' + b'A'
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} else {
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*byte
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}
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}
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}
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fn case04_branch_and_mask(bytes: &mut [u8]) {
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for byte in bytes {
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*byte = if b'a' <= *byte && *byte <= b'z' {
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*byte & !0x20
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} else {
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*byte
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}
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}
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}
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fn case05_branchless(bytes: &mut [u8]) {
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for byte in bytes {
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*byte = branchless_to_ascii_upper_case(*byte)
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}
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}
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fn case06_libcore(bytes: &mut [u8]) {
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bytes.make_ascii_uppercase()
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}
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fn case07_fake_simd_u32(bytes: &mut [u8]) {
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// SAFETY: transmuting a sequence of `u8` to `u32` is always fine
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let (before, aligned, after) = unsafe {
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bytes.align_to_mut::<u32>()
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};
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for byte in before {
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*byte = branchless_to_ascii_upper_case(*byte)
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}
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for word in aligned {
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// FIXME: this is incorrect for some byte values:
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// addition within a byte can carry/overflow into the next byte.
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// Test case: b"\xFFz "
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*word &= !(
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(
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word.wrapping_add(0x1f1f1f1f) &
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!word.wrapping_add(0x05050505) &
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0x80808080
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) >> 2
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)
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}
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for byte in after {
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*byte = branchless_to_ascii_upper_case(*byte)
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}
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}
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fn case08_fake_simd_u64(bytes: &mut [u8]) {
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// SAFETY: transmuting a sequence of `u8` to `u64` is always fine
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let (before, aligned, after) = unsafe {
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bytes.align_to_mut::<u64>()
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};
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for byte in before {
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*byte = branchless_to_ascii_upper_case(*byte)
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}
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for word in aligned {
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// FIXME: like above, this is incorrect for some byte values.
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*word &= !(
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(
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word.wrapping_add(0x1f1f1f1f_1f1f1f1f) &
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!word.wrapping_add(0x05050505_05050505) &
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0x80808080_80808080
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) >> 2
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)
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}
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for byte in after {
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*byte = branchless_to_ascii_upper_case(*byte)
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}
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}
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fn case09_mask_mult_bool_branchy_lookup_table(bytes: &mut [u8]) {
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fn is_ascii_lowercase(b: u8) -> bool {
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if b >= 0x80 { return false }
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match ASCII_CHARACTER_CLASS[b as usize] {
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L | Lx => true,
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_ => false,
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}
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}
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for byte in bytes {
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*byte &= !(0x20 * (is_ascii_lowercase(*byte) as u8))
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}
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}
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fn case10_mask_mult_bool_lookup_table(bytes: &mut [u8]) {
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fn is_ascii_lowercase(b: u8) -> bool {
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match ASCII_CHARACTER_CLASS[b as usize] {
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L | Lx => true,
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_ => false
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}
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}
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for byte in bytes {
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*byte &= !(0x20 * (is_ascii_lowercase(*byte) as u8))
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}
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}
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fn case11_mask_mult_bool_match_range(bytes: &mut [u8]) {
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fn is_ascii_lowercase(b: u8) -> bool {
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match b {
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b'a'..=b'z' => true,
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_ => false
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}
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}
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for byte in bytes {
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*byte &= !(0x20 * (is_ascii_lowercase(*byte) as u8))
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}
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}
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fn case12_mask_shifted_bool_match_range(bytes: &mut [u8]) {
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fn is_ascii_lowercase(b: u8) -> bool {
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match b {
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b'a'..=b'z' => true,
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_ => false
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}
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}
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for byte in bytes {
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*byte &= !((is_ascii_lowercase(*byte) as u8) << 5)
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}
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}
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fn case13_subtract_shifted_bool_match_range(bytes: &mut [u8]) {
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fn is_ascii_lowercase(b: u8) -> bool {
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match b {
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b'a'..=b'z' => true,
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_ => false
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}
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}
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for byte in bytes {
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*byte -= (is_ascii_lowercase(*byte) as u8) << 5
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}
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}
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fn case14_subtract_multiplied_bool_match_range(bytes: &mut [u8]) {
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fn is_ascii_lowercase(b: u8) -> bool {
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match b {
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b'a'..=b'z' => true,
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_ => false
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}
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}
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for byte in bytes {
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*byte -= (b'a' - b'A') * is_ascii_lowercase(*byte) as u8
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}
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}
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@iter
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is_ascii,
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is_ascii_alphabetic,
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is_ascii_uppercase,
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is_ascii_lowercase,
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is_ascii_alphanumeric,
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is_ascii_digit,
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is_ascii_hexdigit,
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is_ascii_punctuation,
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is_ascii_graphic,
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is_ascii_whitespace,
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is_ascii_control,
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}
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macro_rules! repeat {
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($s: expr) => {
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concat!($s, $s, $s, $s, $s, $s, $s, $s, $s, $s)
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};
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}
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const SHORT: &'static str = "Alice's";
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const MEDIUM: &'static str = "Alice's Adventures in Wonderland";
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const LONG: &'static str = repeat!(
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r#"
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La Guida di Bragia, a Ballad Opera for the Marionette Theatre (around 1850)
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Alice's Adventures in Wonderland (1865)
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Phantasmagoria and Other Poems (1869)
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Through the Looking-Glass, and What Alice Found There
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(includes "Jabberwocky" and "The Walrus and the Carpenter") (1871)
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The Hunting of the Snark (1876)
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Rhyme? And Reason? (1883) – shares some contents with the 1869 collection,
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including the long poem "Phantasmagoria"
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A Tangled Tale (1885)
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Sylvie and Bruno (1889)
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Sylvie and Bruno Concluded (1893)
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Pillow Problems (1893)
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What the Tortoise Said to Achilles (1895)
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Three Sunsets and Other Poems (1898)
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The Manlet (1903)[106]
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"#
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);
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#[rustfmt::skip]
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const 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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C, // control
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Cw, // control whitespace
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W, // whitespace
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D, // digit
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L, // lowercase
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Lx, // lowercase hex digit
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U, // uppercase
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Ux, // uppercase hex digit
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P, // punctuation
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N, // Non-ASCII
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}
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use self::AsciiCharacterClass::*;
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#[rustfmt::skip]
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static ASCII_CHARACTER_CLASS: [AsciiCharacterClass; 256] = [
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// _0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _a _b _c _d _e _f
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C, C, C, C, C, C, C, C, C, Cw,Cw,C, Cw,Cw,C, C, // 0_
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C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, // 1_
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W, P, P, P, P, P, P, P, P, P, P, P, P, P, P, P, // 2_
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D, D, D, D, D, D, D, D, D, D, P, P, P, P, P, P, // 3_
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P, Ux,Ux,Ux,Ux,Ux,Ux,U, U, U, U, U, U, U, U, U, // 4_
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U, U, U, U, U, U, U, U, U, U, U, P, P, P, P, P, // 5_
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P, Lx,Lx,Lx,Lx,Lx,Lx,L, L, L, L, L, L, L, L, L, // 6_
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L, L, L, L, L, L, L, L, L, L, L, P, P, P, P, C, // 7_
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N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
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N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
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N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
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N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
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N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
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N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
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N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
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N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
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];
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