AVX2

2023/day1/src/main.rs

@@ -3,6 +3,7 @@ use std::mem::MaybeUninit;
 mod branchless;
 mod naive;
 mod no_lines;
+mod vectorized;
 mod zero_alloc;
 
 fn main() {
@@ -24,6 +25,7 @@ fn main() {
         "zero_alloc" => zero_alloc::part2(&input),
         "branchless" => unsafe { branchless::part2(&input) },
         "no_lines" => unsafe { no_lines::part2(&input) },
+        "vectorized" => unsafe { vectorized::part2(&input) },
         _ => {
             eprintln!("error: invalid mode, must be part1,naive,zero_alloc,branchless");
             std::process::exit(1);

2023/day1/src/no_lines.rs

@@ -14,7 +14,12 @@ pub unsafe fn part2(input: &str) {
         // in the integer bytes:
         // X X X X X e n o
         // this out of bounds read is UB under SB, but fine under models that don't do provenance narrowing with slices. i dont care enough to fix it.
-        let block = bytes.as_ptr().add(byte_idx).cast::<u64>().read_unaligned().to_le();
+        let block = bytes
+            .as_ptr()
+            .add(byte_idx)
+            .cast::<u64>()
+            .read_unaligned()
+            .to_le();
 
         let one = (block & ((1 << (8 * 1)) - 1)) as u8;
         let three = block & ((1 << (8 * 3)) - 1);

2023/day1/src/vectorized.rs

@@ -0,0 +1,147 @@
+pub unsafe fn part2(input: &str) {
+    let mut sum = 0;
+
+    let bytes = input.as_bytes();
+
+    let mut digits = [0_u8; 128];
+
+    let mut byte_idx = 0;
+    let mut line_idx = 0;
+
+    #[cfg(target_arch = "x86_64")]
+    let avx2 = std::arch::is_x86_feature_detected!("avx2");
+    #[cfg(not(target_arch = "x86_64"))]
+    let avx2 = false;
+
+    while byte_idx < bytes.len() {
+        // in memory:
+        // o n e X X X X X
+        // in the integer bytes:
+        // X X X X X e n o
+        // this out of bounds read is UB under SB, but fine under models that don't do provenance narrowing with slices. i dont care enough to fix it.
+        let block = bytes
+            .as_ptr()
+            .add(byte_idx)
+            .cast::<u64>()
+            .read_unaligned()
+            .to_le();
+
+        let one = (block & ((1 << (8 * 1)) - 1)) as u8;
+        let three = block & ((1 << (8 * 3)) - 1);
+        let four = block & ((1 << (8 * 4)) - 1);
+        let five = block & ((1 << (8 * 5)) - 1);
+
+        if one == b'\n' {
+            let first = digits[..line_idx].iter().find(|&&d| d > b'0').unwrap();
+            let last = digits[..line_idx]
+                .iter()
+                .rev()
+                .find(|&&d| d > b'0')
+                .unwrap();
+
+            let first = (first - b'0') as u64;
+            let last = (last - b'0') as u64;
+            sum += first * 10 + last;
+            digits = [0_u8; 128];
+            line_idx = 0;
+            byte_idx += 1;
+            continue;
+        }
+
+        const fn gorble(s: &[u8]) -> u64 {
+            let mut bytes = [0; 8];
+            let mut i = 0;
+            while i < s.len() {
+                bytes[7 - i] = s[i];
+                i += 1;
+            }
+            // like: u64::from_be_bytes([0, 0, 0, b't', b'h', b'g', b'i', b'e'])
+            u64::from_be_bytes(bytes)
+        }
+
+        let mut acc = 0;
+
+
+        acc |= if one >= b'0' && one <= b'9' { one } else { 0 };
+
+        #[cfg(all(target_arch = "x86_64"))]
+        if avx2 {
+            use std::arch::x86_64;
+            unsafe fn round(input: u64, compare: [u64; 4], then: [u64; 4]) -> x86_64::__m256i {
+                // YYYYYYYY|AAAAAAAA|XXXXXXXX|BBBBBBBB|
+                let fives = unsafe { std::mem::transmute::<_, x86_64::__m256i>(compare) };
+                // 000000EE|000000ZZ|000000XX|000000FF|
+                let then = unsafe { std::mem::transmute::<_, x86_64::__m256i>(then) };
+                // XXXXXXXX|XXXXXXXX|XXXXXXXX|XXXXXXXX|
+                let actual = x86_64::_mm256_set1_epi64x(input as i64);
+                // 00000000|00000000|11111111|00000000|
+                let mask = x86_64::_mm256_cmpeq_epi64(fives, actual);
+                // 00000000|00000000|0000000X|00000000|
+                let result = x86_64::_mm256_and_si256(then, mask);
+                // we can also pretend that it's this as only the lowest byte is set in each lane
+                // 0000/0000|0000/0000|0000/000X|0000/0000|
+                result
+            }
+
+            let fives = round(
+                five,
+                [gorble(b"eight"), gorble(b"seven"), gorble(b"three"), 0],
+                [b'8' as _, b'7' as _, b'3' as _, 0],
+            );
+            let fours = round(
+                four,
+                [gorble(b"five"), gorble(b"four"), gorble(b"nine"), 0],
+                [b'5' as _, b'4' as _, b'9' as _, 0],
+            );
+            let threes = round(
+                three,
+                [gorble(b"six"), gorble(b"two"), gorble(b"one"), 0],
+                [b'6' as _, b'2' as _, b'1' as _, 0],
+            );
+
+
+            let result = x86_64::_mm256_or_pd(std::mem::transmute(fives), std::mem::transmute(fours));
+            let result = x86_64::_mm256_or_pd(result, std::mem::transmute(threes));
+
+            let low = x86_64::_mm256_extractf128_pd(result, 0);
+            let high = x86_64::_mm256_extractf128_pd(result, 1);
+            let result = x86_64::_mm_or_pd(low, high);
+            let result = std::mem::transmute::<_, x86_64::__m128i>(result);
+            let low = x86_64::_mm_extract_epi64(result, 0);
+            let high = x86_64::_mm_extract_epi64(result, 1);
+            let result = low | high;
+            debug_assert!(result < 128);
+
+            digits[line_idx] = acc | result as u8;
+
+        }
+
+        if !avx2 {
+            macro_rules! check {
+                ($const:ident $len:ident == $str:expr => $value:expr) => {
+                    const $const: u64 = gorble($str);
+                    acc |= (if $len == $const { $value } else { 0 });
+                };
+            }
+    
+            check!(EIGHT five == b"eight" => b'8');
+            check!(SEVEN five == b"seven" => b'7');
+            check!(THREE five == b"three" => b'3');
+
+            check!(FIVE four == b"five" => b'5');
+            check!(FOUR four == b"four" => b'4');
+            check!(NINE four == b"nine" => b'9');
+
+            check!(SIX three == b"six" => b'6');
+            check!(TWO three == b"two" => b'2');
+            check!(ONE three == b"one" => b'1');
+
+            digits[line_idx] = acc;
+        }
+
+        byte_idx += 1;
+        line_idx += 1;
+    }
+
+    println!("part2: {sum}");
+}