Optimize lines_crlf

src/byte_chunk.rs

@@ -37,6 +37,9 @@ pub(crate) trait ByteChunk: Copy + Clone {
     /// Shifts bytes back lexographically by n bytes.
     fn shift_back_lex(&self, n: usize) -> Self;
 
+    /// Shifts the bottom byte of self into the top byte of n.
+    fn shift_across(&self, n: Self) -> Self;
+
     /// Shifts bits to the right by n bits.
     fn shr(&self, n: usize) -> Self;
 
@@ -100,6 +103,16 @@ impl ByteChunk for usize {
         }
     }
 
+    #[inline(always)]
+    fn shift_across(&self, n: Self) -> Self {
+        let shift_distance = (Self::SIZE - 1) * 8;
+        if cfg!(target_endian = "little") {
+            (*self >> shift_distance) | (n << 8)
+        } else {
+            (*self << shift_distance) | (n >> 8)
+        }
+    }
+
     #[inline(always)]
     fn shr(&self, n: usize) -> Self {
         *self >> n
@@ -198,6 +211,15 @@ impl ByteChunk for x86_64::__m128i {
         }
     }
 
+    #[inline(always)]
+    fn shift_across(&self, n: Self) -> Self {
+        unsafe {
+            let bottom_byte = x86_64::_mm_srli_si128(*self, 15);
+            let rest_shifted = x86_64::_mm_slli_si128(n, 1);
+            x86_64::_mm_or_si128(bottom_byte, rest_shifted)
+        }
+    }
+
     #[inline(always)]
     fn shr(&self, n: usize) -> Self {
         match n {
@@ -292,6 +314,11 @@ impl ByteChunk for aarch64::uint8x16_t {
         }
     }
 
+    #[inline(always)]
+    fn shift_across(&self, n: Self) -> Self {
+        unsafe { aarch64::vextq_u8(*self, n, 15) }
+    }
+
     #[inline(always)]
     fn shr(&self, n: usize) -> Self {
         unsafe {

src/lines_crlf.rs

@@ -55,6 +55,8 @@ pub fn to_byte_idx(text: &str, line_idx: usize) -> usize {
 }
 
 //-------------------------------------------------------------
+const LF: u8 = b'\n';
+const CR: u8 = b'\r';
 
 #[inline(always)]
 fn to_byte_idx_impl<T: ByteChunk>(text: &[u8], line_idx: usize) -> usize {
@@ -68,75 +70,80 @@ fn to_byte_idx_impl<T: ByteChunk>(text: &[u8], line_idx: usize) -> usize {
     let mut break_count = 0;
 
     // Take care of any unaligned bytes at the beginning.
-    for byte in start.iter() {
+    let mut last_was_cr = false;
+    for byte in start.iter().copied() {
+        let is_lf = byte == LF;
+        let is_cr = byte == CR;
         if break_count == line_idx {
-            break;
+            if last_was_cr && is_lf {
+                byte_count += 1;
+            }
+            return byte_count;
+        }
+        if is_cr || (is_lf && !last_was_cr) {
+            break_count += 1;
         }
-        break_count +=
-            (*byte == 0x0A || (*byte == 0x0D && text.get(byte_count + 1) != Some(&0x0A))) as usize;
+        last_was_cr = is_cr;
         byte_count += 1;
     }
 
-    // Process chunks in the fast path.
-    let mut chunks = middle;
-    let mut max_round_len = (line_idx - break_count) / T::MAX_ACC;
-    while max_round_len > 0 && !chunks.is_empty() {
-        // Choose the largest number of chunks we can do this round
-        // that will neither overflow `max_acc` nor blast past the
-        // remaining line breaks we're looking for.
-        let round_len = T::MAX_ACC.min(max_round_len).min(chunks.len());
-        max_round_len -= round_len;
-        let round = &chunks[..round_len];
-        chunks = &chunks[round_len..];
-
-        // Process the chunks in this round.
-        let mut acc = T::zero();
-        for chunk in round.iter() {
-            let lf_flags = chunk.cmp_eq_byte(0x0A);
-            let cr_flags = chunk.cmp_eq_byte(0x0D);
-            let crlf_flags = cr_flags.bitand(lf_flags.shift_back_lex(1));
-            acc = acc.add(lf_flags).add(cr_flags.sub(crlf_flags));
-        }
-        break_count += acc.sum_bytes();
-
-        // Handle CRLFs at chunk boundaries in this round.
-        let mut i = byte_count;
-        while i < (byte_count + T::SIZE * round_len) {
-            i += T::SIZE;
-            break_count -= (text[i - 1] == 0x0D && text.get(i) == Some(&0x0A)) as usize;
+    // Process the chunks 2 at a time.
+    let mut chunk_count = 0;
+    let mut prev = T::splat(last_was_cr as u8);
+    for chunks in middle.chunks_exact(2) {
+        let lf_flags0 = chunks[0].cmp_eq_byte(LF);
+        let cr_flags0 = chunks[0].cmp_eq_byte(CR);
+        let crlf_flags0 = prev.shift_across(cr_flags0).bitand(lf_flags0);
+
+        let lf_flags1 = chunks[1].cmp_eq_byte(LF);
+        let cr_flags1 = chunks[1].cmp_eq_byte(CR);
+        let crlf_flags1 = cr_flags0.shift_across(cr_flags1).bitand(lf_flags1);
+        let new_break_count = break_count
+            + lf_flags0
+                .add(cr_flags0)
+                .add(lf_flags1)
+                .add(cr_flags1)
+                .sub(crlf_flags0)
+                .sub(crlf_flags1)
+                .sum_bytes();
+        if new_break_count >= line_idx {
+            break;
         }
-
-        byte_count += T::SIZE * round_len;
+        break_count = new_break_count;
+        byte_count += T::SIZE * 2;
+        chunk_count += 2;
+        prev = cr_flags1;
     }
 
-    // Process chunks in the slow path.
-    for chunk in chunks.iter() {
-        let breaks = {
-            let lf_flags = chunk.cmp_eq_byte(0x0A);
-            let cr_flags = chunk.cmp_eq_byte(0x0D);
-            let crlf_flags = cr_flags.bitand(lf_flags.shift_back_lex(1));
-            lf_flags.add(cr_flags.sub(crlf_flags)).sum_bytes()
-        };
-        let boundary_crlf = {
-            let i = byte_count + T::SIZE;
-            (text[i - 1] == 0x0D && text.get(i) == Some(&0x0A)) as usize
-        };
-        let new_break_count = break_count + breaks - boundary_crlf;
+    // Process the rest of the chunks.
+    for chunk in middle[chunk_count..].iter() {
+        let lf_flags = chunk.cmp_eq_byte(LF);
+        let cr_flags = chunk.cmp_eq_byte(CR);
+        let crlf_flags = prev.shift_across(cr_flags).bitand(lf_flags);
+        let new_break_count = break_count + lf_flags.add(cr_flags).sub(crlf_flags).sum_bytes();
         if new_break_count >= line_idx {
             break;
         }
         break_count = new_break_count;
         byte_count += T::SIZE;
+        prev = cr_flags;
     }
 
     // Take care of any unaligned bytes at the end.
-    let end = &text[byte_count..];
-    for byte in end.iter() {
+    last_was_cr = text.get(byte_count.saturating_sub(1)) == Some(&CR);
+    for byte in text[byte_count..].iter().copied() {
+        let is_lf = byte == LF;
+        let is_cr = byte == CR;
         if break_count == line_idx {
+            if last_was_cr && is_lf {
+                byte_count += 1;
+            }
             break;
         }
-        break_count +=
-            (*byte == 0x0A || (*byte == 0x0D && text.get(byte_count + 1) != Some(&0x0A))) as usize;
+        if is_cr || (is_lf && !last_was_cr) {
+            break_count += 1;
+        }
+        last_was_cr = is_cr;
         byte_count += 1;
     }
 
@@ -159,38 +166,44 @@ fn count_breaks_impl<T: ByteChunk>(text: &[u8]) -> usize {
     // Take care of unaligned bytes at the beginning.
     let mut last_was_cr = false;
     for byte in start.iter().copied() {
-        let is_lf = byte == 0x0A;
-        let is_cr = byte == 0x0D;
+        let is_lf = byte == LF;
+        let is_cr = byte == CR;
         count += (is_cr | (is_lf & !last_was_cr)) as usize;
         last_was_cr = is_cr;
     }
 
     // Take care of the middle bytes in big chunks.
-    for chunks in middle.chunks(T::MAX_ACC) {
-        let mut acc = T::zero();
-        for chunk in chunks.iter() {
-            let lf_flags = chunk.cmp_eq_byte(0x0A);
-            let cr_flags = chunk.cmp_eq_byte(0x0D);
-            let crlf_flags = cr_flags.bitand(lf_flags.shift_back_lex(1));
-            acc = acc.add(lf_flags).add(cr_flags.sub(crlf_flags));
-        }
-        count += acc.sum_bytes();
+    let mut prev = T::splat(last_was_cr as u8);
+    for chunks in middle.chunks_exact(2) {
+        let lf_flags0 = chunks[0].cmp_eq_byte(LF);
+        let cr_flags0 = chunks[0].cmp_eq_byte(CR);
+        let crlf_flags0 = prev.shift_across(cr_flags0).bitand(lf_flags0);
+
+        let lf_flags1 = chunks[1].cmp_eq_byte(LF);
+        let cr_flags1 = chunks[1].cmp_eq_byte(CR);
+        let crlf_flags1 = cr_flags0.shift_across(cr_flags1).bitand(lf_flags1);
+        count += lf_flags0
+            .add(cr_flags0)
+            .sub(crlf_flags0)
+            .add(lf_flags1)
+            .add(cr_flags1)
+            .sub(crlf_flags1)
+            .sum_bytes();
+        prev = cr_flags1;
     }
 
-    // Check chunk boundaries for CRLF.
-    let mut i = start.len();
-    while i < (text.len() - end.len()) {
-        if text[i] == 0x0A {
-            count -= (text.get(i.saturating_sub(1)) == Some(&0x0D)) as usize;
-        }
-        i += T::SIZE;
+    if let Some(chunk) = middle.chunks_exact(2).remainder().iter().next() {
+        let lf_flags = chunk.cmp_eq_byte(LF);
+        let cr_flags = chunk.cmp_eq_byte(CR);
+        let crlf_flags = prev.shift_across(cr_flags).bitand(lf_flags);
+        count += lf_flags.add(cr_flags).sub(crlf_flags).sum_bytes();
     }
 
     // Take care of unaligned bytes at the end.
-    let mut last_was_cr = text.get((text.len() - end.len()).saturating_sub(1)) == Some(&0x0D);
+    last_was_cr = text.get((text.len() - end.len()).saturating_sub(1)) == Some(&CR);
     for byte in end.iter().copied() {
-        let is_lf = byte == 0x0A;
-        let is_cr = byte == 0x0D;
+        let is_lf = byte == LF;
+        let is_cr = byte == CR;
         count += (is_cr | (is_lf & !last_was_cr)) as usize;
         last_was_cr = is_cr;
     }

tests/proptests_lines_crlf.proptest-regressions

@@ -6,3 +6,7 @@
 # everyone who runs the test benefits from these saved cases.
 cc 7332c47dc044064cfb86ac6d94c45441f6dcdab699402718874116b512062e0a # shrinks to ref text = "a\n\rあ\r\n\rあa\n\rあ\n\nあ\r\nああ\r\nあ🐸a\ra\r🐸", idx = 48
 cc f9a60685ebb7fc415f3d941598e75c90a0a7db0f0cd6673e092cf78f43a60fa3 # shrinks to ref text = "あああ\r\r\r\n\naaあ\naあ\r🐸🐸🐸\n\naあaaa\n🐸\na\n\na\n\n\n\r\n🐸\r\nあ\raaああ🐸a\naa🐸\n🐸\ra\na🐸a🐸\n\ra\n🐸🐸🐸\r\ra🐸あ\n\n🐸🐸aaあ\r\rあ🐸\rあa\n\r\n🐸🐸\n\nあ\rあa\nあa\rあaa\nあa\r\r\r\n\r\n\r\nあa🐸\r\n\r\r\na\r"
+cc 3e5415f317b24c22a479d0e56a4705ad4c4c0cb060ee5610f94ef78fe3fda588 # shrinks to ref text = "\n\r\raa🐸\ra\n\raa🐸あ\r\n\n\nあ\nあ🐸🐸あ🐸\n🐸あああ🐸aaあ🐸a\n\rあああ🐸あ🐸\n\n\r🐸a\rああ\r🐸ああ\n\r\r\r🐸🐸あ🐸\r\r\n🐸🐸あaa\r\na\r\n🐸\na🐸\raあ\r\naあa\nああ\r\r🐸a\n\raa\rあ🐸\rあ\n\n\rあ\n\r\n🐸ああ\n🐸aあ\r\r\n\nあ🐸a\naaa🐸🐸あa", idx = 272
+cc 9fe71a1c06b7b4791fab564d43a9fe7e0d3047302e6c9228852e91f638833aae # shrinks to ref text = "\n\n\nあああaa\n🐸\rああ\r🐸🐸あ\n\nああ🐸\n\rああ\r\n🐸\nああ🐸\n\ra\r\r\naあ\n🐸\rあ\n\r", idx = 96
+cc b06906825a8db53b794a8dfbd9fc17ee80d3f722528a86644ad4457ba8ab12d8 # shrinks to ref text = "🐸\n\ra🐸\n🐸aaa\r🐸aaaa🐸🐸\nあ\r\naあ\rあa\raあ\rあ\rあa\ra\n\nあa\rあ\r\rあa\nああaa\n\r🐸\na\n🐸あ🐸a\r\n\n\naあa\raaa\r🐸🐸\r\rあaあ🐸\n🐸🐸\rあ\nああああaa\na\r\n\raa\n🐸\naあ\raaaa\n\n\naaあa🐸🐸🐸\ra\nあ\n\nあ🐸ああ🐸a🐸a\rあ\rあ🐸🐸あ🐸あa\n\raaあ\r🐸あ\ra\na🐸🐸\r\rあa\r\n\n\nあ\r\r\r🐸あ🐸🐸🐸\r\rあaあ🐸\n\n\r🐸\n🐸あ\r"
+cc 8e3c6ad1951e8839368157cf7f595661bbf5b004ff19800499d42387e6b8fe56 # shrinks to ref text = "🐸あ🐸🐸🐸\ra\nあ🐸aああ\rあ🐸ああ\n\rあa\r\raa\n\naa🐸\ra\n\r🐸\nあ\n\r🐸\raaa🐸🐸🐸aあ\raあ🐸\na\n🐸aaあ\naあ\n🐸🐸あa\r\r🐸\r🐸a🐸aaaああ🐸\naあ\na\n\naa\n\r🐸\r\ra\r🐸\n\n\n\n\n\r\nあ\rあa\nあ\ra🐸\r\n🐸\n\ra\r\r\n\n\nあa\r\rあ🐸\n🐸\n🐸\r\rあ🐸\r🐸🐸あ🐸a\nあああ🐸🐸aaaa🐸\n🐸\r\r\na\n\r🐸a🐸aa\n\n\r\r\r\r🐸\r🐸🐸", idx = 69