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/// SWAR: SIMD Within A Register
/// SIMD validator backend that validates register-sized chunks of data at a time.
use crate::{is_header_name_token, is_header_value_token, is_uri_token, Bytes};
// Adapt block-size to match native register size, i.e: 32bit => 4, 64bit => 8
const BLOCK_SIZE: usize = core::mem::size_of::<usize>();
type ByteBlock = [u8; BLOCK_SIZE];
#[inline]
pub fn match_uri_vectored(bytes: &mut Bytes) {
loop {
if let Some(bytes8) = bytes.peek_n::<ByteBlock>(BLOCK_SIZE) {
let n = match_uri_char_8_swar(bytes8);
// SAFETY: using peek_n to retrieve the bytes ensures that there are at least n more bytes
// in `bytes`, so calling `advance(n)` is safe.
unsafe {
bytes.advance(n);
}
if n == BLOCK_SIZE {
continue;
}
}
if let Some(b) = bytes.peek() {
if is_uri_token(b) {
// SAFETY: using peek to retrieve the byte ensures that there is at least 1 more byte
// in bytes, so calling advance is safe.
unsafe {
bytes.advance(1);
}
continue;
}
}
break;
}
}
#[inline]
pub fn match_header_value_vectored(bytes: &mut Bytes) {
loop {
if let Some(bytes8) = bytes.peek_n::<ByteBlock>(BLOCK_SIZE) {
let n = match_header_value_char_8_swar(bytes8);
// SAFETY: using peek_n to retrieve the bytes ensures that there are at least n more bytes
// in `bytes`, so calling `advance(n)` is safe.
unsafe {
bytes.advance(n);
}
if n == BLOCK_SIZE {
continue;
}
}
if let Some(b) = bytes.peek() {
if is_header_value_token(b) {
// SAFETY: using peek to retrieve the byte ensures that there is at least 1 more byte
// in bytes, so calling advance is safe.
unsafe {
bytes.advance(1);
}
continue;
}
}
break;
}
}
#[inline]
pub fn match_header_name_vectored(bytes: &mut Bytes) {
while let Some(block) = bytes.peek_n::<ByteBlock>(BLOCK_SIZE) {
let n = match_block(is_header_name_token, block);
// SAFETY: using peek_n to retrieve the bytes ensures that there are at least n more bytes
// in `bytes`, so calling `advance(n)` is safe.
unsafe {
bytes.advance(n);
}
if n != BLOCK_SIZE {
return;
}
}
// SAFETY: match_tail processes at most the remaining data in `bytes`. advances `bytes` to the
// end, but no further.
unsafe { bytes.advance(match_tail(is_header_name_token, bytes.as_ref())) };
}
// Matches "tail", i.e: when we have <BLOCK_SIZE bytes in the buffer, should be uncommon
#[cold]
#[inline]
fn match_tail(f: impl Fn(u8) -> bool, bytes: &[u8]) -> usize {
for (i, &b) in bytes.iter().enumerate() {
if !f(b) {
return i;
}
}
bytes.len()
}
// Naive fallback block matcher
#[inline(always)]
fn match_block(f: impl Fn(u8) -> bool, block: ByteBlock) -> usize {
for (i, &b) in block.iter().enumerate() {
if !f(b) {
return i;
}
}
BLOCK_SIZE
}
// A const alternative to u64::from_ne_bytes to avoid bumping MSRV (1.36 => 1.44)
// creates a u64 whose bytes are each equal to b
const fn uniform_block(b: u8) -> usize {
(b as u64 * 0x01_01_01_01_01_01_01_01 /* [1_u8; 8] */) as usize
}
// A byte-wise range-check on an enire word/block,
// ensuring all bytes in the word satisfy
// `33 <= x <= 126 && x != '>' && x != '<'`
// IMPORTANT: it false negatives if the block contains '?'
#[inline]
fn match_uri_char_8_swar(block: ByteBlock) -> usize {
// 33 <= x <= 126
const M: u8 = 0x21;
const N: u8 = 0x7E;
const BM: usize = uniform_block(M);
const BN: usize = uniform_block(127 - N);
const M128: usize = uniform_block(128);
let x = usize::from_ne_bytes(block); // Really just a transmute
let lt = x.wrapping_sub(BM) & !x; // <= m
let gt = x.wrapping_add(BN) | x; // >= n
// XOR checks to catch '<' & '>' for correctness
//
// XOR can be thought of as a "distance function"
// (somewhat extrapolating from the `xor(x, x) = 0` identity and ∀ x != y: xor(x, y) != 0`
// (each u8 "xor key" providing a unique total ordering of u8)
// '<' and '>' have a "xor distance" of 2 (`xor('<', '>') = 2`)
// xor(x, '>') <= 2 => {'>', '?', '<'}
// xor(x, '<') <= 2 => {'<', '=', '>'}
//
// We assume P('=') > P('?'),
// given well/commonly-formatted URLs with querystrings contain
// a single '?' but possibly many '='
//
// Thus it's preferable/near-optimal to "xor distance" on '>',
// since we'll slowpath at most one block per URL
//
// Some rust code to sanity check this yourself:
// ```rs
// fn xordist(x: u8, n: u8) -> Vec<(char, u8)> {
// (0..=255).into_iter().map(|c| (c as char, c ^ x)).filter(|(_c, y)| *y <= n).collect()
// }
// (xordist(b'<', 2), xordist(b'>', 2))
// ```
const B3: usize = uniform_block(3); // (dist <= 2) + 1 to wrap
const BGT: usize = uniform_block(b'>');
let xgt = x ^ BGT;
let ltgtq = xgt.wrapping_sub(B3) & !xgt;
offsetnz((ltgtq | lt | gt) & M128)
}
// A byte-wise range-check on an entire word/block,
// ensuring all bytes in the word satisfy `32 <= x <= 126`
// IMPORTANT: false negatives if obs-text is present (0x80..=0xFF)
#[inline]
fn match_header_value_char_8_swar(block: ByteBlock) -> usize {
// 32 <= x <= 126
const M: u8 = 0x20;
const N: u8 = 0x7E;
const BM: usize = uniform_block(M);
const BN: usize = uniform_block(127 - N);
const M128: usize = uniform_block(128);
let x = usize::from_ne_bytes(block); // Really just a transmute
let lt = x.wrapping_sub(BM) & !x; // <= m
let gt = x.wrapping_add(BN) | x; // >= n
offsetnz((lt | gt) & M128)
}
/// Check block to find offset of first non-zero byte
// NOTE: Curiously `block.trailing_zeros() >> 3` appears to be slower, maybe revisit
#[inline]
fn offsetnz(block: usize) -> usize {
// fast path optimistic case (common for long valid sequences)
if block == 0 {
return BLOCK_SIZE;
}
// perf: rust will unroll this loop
for (i, b) in block.to_ne_bytes().iter().copied().enumerate() {
if b != 0 {
return i;
}
}
unreachable!()
}
#[test]
fn test_is_header_value_block() {
let is_header_value_block = |b| match_header_value_char_8_swar(b) == BLOCK_SIZE;
// 0..32 => false
for b in 0..32_u8 {
assert!(!is_header_value_block([b; BLOCK_SIZE]), "b={}", b);
}
// 32..127 => true
for b in 32..127_u8 {
assert!(is_header_value_block([b; BLOCK_SIZE]), "b={}", b);
}
// 127..=255 => false
for b in 127..=255_u8 {
assert!(!is_header_value_block([b; BLOCK_SIZE]), "b={}", b);
}
#[cfg(target_pointer_width = "64")]
{
// A few sanity checks on non-uniform bytes for safe-measure
assert!(!is_header_value_block(*b"foo.com\n"));
assert!(!is_header_value_block(*b"o.com\r\nU"));
}
}
#[test]
fn test_is_uri_block() {
let is_uri_block = |b| match_uri_char_8_swar(b) == BLOCK_SIZE;
// 0..33 => false
for b in 0..33_u8 {
assert!(!is_uri_block([b; BLOCK_SIZE]), "b={}", b);
}
// 33..127 => true if b not in { '<', '?', '>' }
let falsy = |b| b"<?>".contains(&b);
for b in 33..127_u8 {
assert_eq!(is_uri_block([b; BLOCK_SIZE]), !falsy(b), "b={}", b);
}
// 127..=255 => false
for b in 127..=255_u8 {
assert!(!is_uri_block([b; BLOCK_SIZE]), "b={}", b);
}
}
#[test]
fn test_offsetnz() {
let seq = [0_u8; BLOCK_SIZE];
for i in 0..BLOCK_SIZE {
let mut seq = seq;
seq[i] = 1;
let x = usize::from_ne_bytes(seq);
assert_eq!(offsetnz(x), i);
}
}