refactor: prevent some allocations for perf

src/main.rs

@@ -456,12 +456,9 @@ fn main() -> Result<()> {
 
             let mut sha1 = Sha1::default();
             let mut buffer = itoa::Buffer::new();
+            let mut count_buffer = itoa::Buffer::new();
             let mut first = true;
-            loop {
-                if found.load(Ordering::SeqCst) {
-                    break;
-                }
-
+            while !found.load(Ordering::SeqCst) {
                 let append = if gpg.is_some() || seq_key.is_some() {
                     None
                 } else {
@@ -469,11 +466,11 @@ fn main() -> Result<()> {
                         Method::Random => {
                             let mut bytes = [0; 16];
                             rand::thread_rng().fill(&mut bytes);
-                            Some(data_encoding::HEXLOWER.encode(&bytes))
+                            Some(Cow::from(data_encoding::HEXLOWER.encode(&bytes)))
                         }
                         Method::Counter => {
                             let count = counter.fetch_add(1, Ordering::SeqCst) + 1;
-                            Some(buffer.format(count).to_owned())
+                            Some(Cow::from(count_buffer.format(count)))
                         }
                         _ => None,
                     }
@@ -495,18 +492,21 @@ fn main() -> Result<()> {
 
                 if method == Method::Header {
                     let count = counter.fetch_add(1, Ordering::SeqCst) + 1;
-                    let line = format!("xvain {}", buffer.format(count));
                     if first {
-                        header_lines.insert(committer_idx + 1, line);
-                    } else {
-                        header_lines[committer_idx + 1] = line;
+                        header_lines.insert(committer_idx + 1, String::with_capacity(16));
+                        first = false;
                     }
 
-                    first = false;
+                    let line = &mut header_lines[committer_idx + 1];
+                    line.clear();
+                    line.push_str("xvain ");
+                    line.push_str(buffer.format(count));
                 }
 
                 let mut header = header_lines.join("\n");
 
+                // NOTE: don't need to handle append here, since we'll never be
+                //       both appending *and* signing
                 if let Some(ctx) = &mut gpg {
                     let to_sign = format!("{header}\n{message}");
                     let mut output = Vec::new();
@@ -570,7 +570,7 @@ fn main() -> Result<()> {
                     Some(a) => {
                         sha1.update(&message);
                         sha1.update("\n");
-                        sha1.update(a);
+                        sha1.update(a.as_bytes());
                         sha1.update("\n");
                     }
                     None => sha1.update(&message),