diff --git a/calculate/src/main.rs b/calculate/src/main.rs
index bd2b185..409d87b 100644
--- a/calculate/src/main.rs
+++ b/calculate/src/main.rs
@@ -1,3 +1,5 @@
+#![feature(portable_simd)]
+
 use ::{
     anyhow::Result,
     clap::{Parser, ValueEnum},
diff --git a/calculate/src/optimized.rs b/calculate/src/optimized.rs
index 79ab840..b5bbfc2 100644
--- a/calculate/src/optimized.rs
+++ b/calculate/src/optimized.rs
@@ -10,6 +10,7 @@ use {
     std::{
         fs::File,
         io::{BufWriter, Write},
+        simd::prelude::*,
     },
 };
 
@@ -33,7 +34,12 @@ pub(crate) fn run(args: Args) -> Result<()> {
     input.advise(Advice::Sequential)?;
     input.advise(Advice::WillNeed)?;
 
-    let input = &input[..];
+    let mut input = &input[..];
+    while input.first() == Some(&b'#') {
+        let pos_nl = memchr(b'\n', input).context("bad input")?;
+        input = &input[pos_nl + 1..];
+    }
+
     let style: ProgressStyle = ProgressStyle::with_template(
         "[{elapsed}/{duration}] [{bar}] {percent}% ({binary_bytes_per_sec})",
     )
@@ -134,6 +140,9 @@ fn parse_temp(input: &[u8], sep_pos: usize, nl_pos: usize) -> i64 {
     sign * (a * 100 + b * 10 + c)
 }
 
+const LANES: usize = 32;
+type Chunk = Simd<u8, LANES>;
+
 fn find_sep(b: &[u8]) -> Option<usize> {
     memchr(b';', b)
 }
@@ -150,7 +159,82 @@ fn chunk<'input, 'bump>(
     let mut data: HashMap<&'bump [u8], Data, RandomState> =
         HashMap::with_capacity_and_hasher(UNIQUE_CITY_COUNT, RandomState::default());
 
+    let sep = Chunk::splat(b';');
+    let nl = Chunk::splat(b'\n');
     let mut pb_since_last_inc: usize = 0;
+    'outer: while input.len() > LANES {
+        if pb_since_last_inc >= 10_000_000 {
+            pb.inc(pb_since_last_inc as u64);
+            pb_since_last_inc = 0;
+        }
+        let chunk = Chunk::from_slice(input);
+        let mut mask_sep = sep.simd_eq(chunk).to_bitmask();
+        let mut mask_nl = nl.simd_eq(chunk).to_bitmask();
+
+        let mut i_sep = 0;
+        if mask_sep == 0 {
+            loop {
+                i_sep += 1;
+                let chunk_input = &input[i_sep * LANES..];
+                if chunk_input.len() < LANES {
+                    break 'outer;
+                }
+                let chunk = Chunk::from_slice(chunk_input);
+                mask_sep = sep.simd_eq(chunk).to_bitmask();
+                mask_nl = nl.simd_eq(chunk).to_bitmask();
+                if mask_sep != 0 {
+                    break;
+                }
+            }
+        }
+
+        let mut i_nl = i_sep;
+        if mask_nl == 0 {
+            loop {
+                i_nl += 1;
+                let chunk_input = &input[i_nl * LANES..];
+                if chunk_input.len() < LANES {
+                    break 'outer;
+                }
+                let chunk = Chunk::from_slice(chunk_input);
+                mask_nl = nl.simd_eq(chunk).to_bitmask();
+                if mask_nl != 0 {
+                    break;
+                }
+            }
+        }
+
+        let offset_sep = mask_sep.trailing_zeros();
+        let offset_nl = mask_nl.trailing_zeros();
+        let pos_sep = LANES * i_sep + offset_sep as usize;
+        let pos_nl = LANES * i_nl + offset_nl as usize;
+
+        let city = unsafe { input.get_unchecked(..pos_sep) };
+        let temperature = parse_temp(input, pos_sep, pos_nl);
+
+        input = &input[pos_nl + 1..];
+        pb_since_last_inc += pos_nl + 1;
+
+        let (_key, data) = data.raw_entry_mut().from_key(city).or_insert_with(|| {
+            (
+                city_bumper.alloc_slice_copy(city),
+                Data {
+                    min: i64::MAX,
+                    max: i64::MIN,
+                    sum: 0,
+                    count: 0,
+                },
+            )
+        });
+        if temperature < data.min {
+            data.min = temperature;
+        }
+        if temperature > data.max {
+            data.max = temperature;
+        }
+        data.sum += temperature;
+        data.count += 1;
+    }
     loop {
         if pb_since_last_inc >= 10_000_000 {
             pb.inc(pb_since_last_inc as u64);
@@ -169,6 +253,7 @@ fn chunk<'input, 'bump>(
         }
         let city = unsafe { input.get_unchecked(..pos_sep) };
         let temperature = parse_temp(input, pos_sep, pos_nl);
+
         input = &input[pos_nl + 1..];
         pb_since_last_inc += pos_nl + 1;