perf: use memory efficient search of str prefix

README.md

@@ -10,7 +10,7 @@
 
 
 [Demo](examples/arduino/README.md) of CLI running on Arduino Nano.
-Memory usage: 15KiB of ROM and 0.5KiB of static RAM. Most of static RAM is used by help strings.
+Memory usage: 14KiB of ROM and 0.5KiB of static RAM. Most of static RAM is used by help strings.
 
 ![Arduino Demo](examples/arduino/demo.gif)
 

embedded-cli/src/autocomplete.rs

@@ -48,7 +48,7 @@ impl<'a> Autocompletion<'a> {
     }
 
     /// Whether autocompletion is partial
-    /// and futher input is required
+    /// and further input is required
     pub fn is_partial(&self) -> bool {
         self.partial
     }
@@ -71,17 +71,12 @@ impl<'a> Autocompletion<'a> {
         // compare new autocompletion to existing and keep
         // only common prefix
         let len = match self.autocompleted() {
-            Some(current) => autocompletion
-                .char_indices()
-                .zip(current.char_indices())
-                .find(|((_, a1), (_, a2))| a1 != a2)
-                .map(|((pos, _), _)| pos)
-                .unwrap_or(current.len().min(autocompletion.len())),
+            Some(current) => utils::common_prefix_len(autocompletion, current),
             None => autocompletion.len(),
         };
 
         if len > self.buffer.len() {
-            // if buffer is full with this autocompletion, there is not much sence in doing it
+            // if buffer is full with this autocompletion, there is not much sense in doing it
             // since user will not be able to type anything else
             // so just do nothing with it
         } else {
@@ -100,7 +95,7 @@ mod tests {
     use crate::autocomplete::Autocompletion;
 
     #[test]
-    fn nomerge() {
+    fn no_merge() {
         let mut input = [0; 64];
 
         let autocompletion = Autocompletion::new(&mut input);

embedded-cli/src/utils.rs

@@ -34,6 +34,27 @@ pub fn char_count(text: &str) -> usize {
     count
 }
 
+/// Returns length (in bytes) of longest common prefix
+pub fn common_prefix_len(left: &str, right: &str) -> usize {
+    let mut accum1 = Utf8Accum::default();
+
+    let mut pos = 0;
+    let mut byte_counter = 0;
+
+    for (&b1, &b2) in left.as_bytes().iter().zip(right.as_bytes().iter()) {
+        if b1 != b2 {
+            break;
+        }
+        let c1 = accum1.push_byte(b1);
+        byte_counter += 1;
+        if c1.is_some() {
+            pos = byte_counter;
+        }
+    }
+
+    pos
+}
+
 /// Function to rotate `buf` by `mid` elements
 ///
 /// Not using `core::slice::rotate_left` since it
@@ -130,4 +151,25 @@ mod tests {
     fn char_count(#[case] text: &str) {
         assert_eq!(utils::char_count(text), text.chars().count())
     }
+
+    #[rstest]
+    #[case("abcdef", "abcdef")]
+    #[case("abcdef", "abc")]
+    #[case("abcdef", "abc ghf")]
+    #[case("abcdef", "")]
+    #[case("", "")]
+    #[case("абв 佐佗佟𑿁", "абв 佐佗佟𑿁")]
+    #[case("абв 佐佗佟𑿁𑿆𑿌", "абв 佐佗佟𑿁")]
+    #[case("абв 佐佗佟𑿁 𑿆𑿌", "абв 佐佗𑿁佟")]
+    fn common_prefix(#[case] left: &str, #[case] right: &str) {
+        let expected = left
+            .char_indices()
+            .zip(right.char_indices())
+            .find(|((_, a1), (_, a2))| a1 != a2)
+            .map(|((pos, _), _)| pos)
+            .unwrap_or(right.len().min(left.len()));
+
+        assert_eq!(utils::common_prefix_len(left, right), expected);
+        assert_eq!(utils::common_prefix_len(right, left), expected);
+    }
 }

examples/arduino/README.md

@@ -2,7 +2,7 @@
 
 This example shows how to build cli with Arduino Nano.
 Another Arduino can also be used, but you will have to tweak configs.
-Example uses ~15KiB of ROM and ~0.5KiB of static RAM.
+Example uses ~14KiB of ROM and ~0.5KiB of static RAM.
 Most of RAM is taken by derived implementations for help and autocomplete
 that don't use progmem. In future this should be fixed.
 
@@ -33,13 +33,13 @@ cargo bloat --release
 Example output:
 ```
 File  .text    Size        Crate Name
-1.6%  54.5%  8.1KiB  arduino_cli arduino_cli::try_run
-0.2%   6.7%   1016B embedded_cli embedded_cli::autocomplete::Autocompletion::merge_autocompletion
-0.1%   3.6%    538B embedded_cli embedded_cli::token::Tokens::new
-0.1%   3.5%    530B embedded_cli embedded_cli::help::HelpRequest::from_tokens
-0.1%   3.1%    472B embedded_cli embedded_cli::token::Tokens::remove
-0.8%  25.4%  3.8KiB              And 34 smaller methods. Use -n N to show more.
-3.0% 100.0% 14.8KiB              .text section size, the file size is 498.4KiB
+1.6%  56.9%  8.1KiB  arduino_cli arduino_cli::try_run
+0.1%   3.7%    538B embedded_cli embedded_cli::token::Tokens::new
+0.1%   3.6%    530B embedded_cli embedded_cli::help::HelpRequest::from_tokens
+0.1%   3.2%    472B embedded_cli embedded_cli::token::Tokens::remove
+0.1%   3.2%    468B embedded_cli embedded_cli::cli::Cli<W,E,CommandBuffer,HistoryBuffer>::navigate_history
+0.7%  26.0%  3.7KiB              And 34 smaller methods. Use -n N to show more.
+2.9% 100.0% 14.2KiB              .text section size, the file size is 493.3KiB
 ```
 
 To find total static memory usage: