fix(swar): allow caret characters when validating uri

Author: nikneym

src/simd/swar.rs

@@ -111,8 +111,7 @@ const fn uniform_block(b: u8) -> 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 '?'
+// `33 <= x <= 126
 #[inline]
 fn match_uri_char_8_swar(block: ByteBlock) -> usize {
     // 33 <= x <= 126
@@ -126,36 +125,7 @@ fn match_uri_char_8_swar(block: ByteBlock) -> usize {
     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)
+    offsetnz((lt | gt) & M128)
 }
 
 // A byte-wise range-check on an entire word/block,
@@ -228,11 +198,6 @@ fn test_is_uri_block() {
     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);