From 596730bf19f04a97ef835b27466998b50f26e230 Mon Sep 17 00:00:00 2001
From: Jesse Luehrs <doy@tozt.net>
Date: Sat, 9 Nov 2019 10:42:44 -0500
Subject: use a fixed size buffer for cell data

this dramatically speeds things up
---
 src/cell.rs   | 78 +++++++++++++++++++++++++++++++++++++++++++++--------------
 src/row.rs    |  2 +-
 tests/text.rs |  8 ++++++
 3 files changed, 69 insertions(+), 19 deletions(-)

diff --git a/src/cell.rs b/src/cell.rs
index d0d6f0c..61a3cd3 100644
--- a/src/cell.rs
+++ b/src/cell.rs
@@ -1,33 +1,73 @@
 use unicode_normalization::UnicodeNormalization as _;
 use unicode_width::UnicodeWidthChar as _;
 
+const CODEPOINTS_IN_CELL: usize = 6;
+
 /// Represents a single terminal cell.
-#[derive(Clone, Debug, Default, Eq, PartialEq)]
+#[derive(Clone, Debug, Default, Eq)]
 pub struct Cell {
-    contents: String,
+    contents: [char; CODEPOINTS_IN_CELL],
+    len: u8,
     attrs: crate::attrs::Attrs,
 }
 
+impl PartialEq<Cell> for Cell {
+    fn eq(&self, other: &Self) -> bool {
+        if self.attrs != other.attrs {
+            return false;
+        }
+        if self.len != other.len {
+            return false;
+        }
+        let len = self.len as usize;
+        self.contents[..len] == other.contents[..len]
+    }
+}
+
 impl Cell {
     pub(crate) fn set(&mut self, c: char, a: crate::attrs::Attrs) {
-        let mut buf = vec![0; 4];
-        c.encode_utf8(&mut buf);
-        self.contents = unsafe { String::from_utf8_unchecked(buf) };
+        self.contents[0] = c;
+        self.len = 1;
         self.attrs = a;
     }
 
     pub(crate) fn append(&mut self, c: char) {
-        self.contents.push(c);
+        if self.len as usize >= CODEPOINTS_IN_CELL {
+            return;
+        }
+
+        self.contents[self.len as usize] = c;
+        self.len += 1;
+
         // some fonts have combined characters but can't render combining
         // characters correctly, so try to prefer precombined characters when
         // possible
-        if !unicode_normalization::is_nfc(&self.contents) {
-            self.contents = self.contents.nfc().collect();
+        if unicode_normalization::is_nfc_quick(
+            self.contents.iter().copied().take(CODEPOINTS_IN_CELL),
+        ) == unicode_normalization::IsNormalized::Yes
+        {
+            return;
         }
+
+        let mut new_contents = ['\x00'; CODEPOINTS_IN_CELL];
+        let mut new_len = 0;
+        for c in self
+            .contents
+            .iter()
+            .copied()
+            .take(self.len as usize)
+            .nfc()
+            .take(CODEPOINTS_IN_CELL)
+        {
+            new_contents[new_len as usize] = c;
+            new_len += 1;
+        }
+        self.contents = new_contents;
+        self.len = new_len;
     }
 
     pub(crate) fn clear(&mut self, bgcolor: crate::attrs::Color) {
-        self.contents.clear();
+        self.len = 0;
         self.attrs.clear();
         self.attrs.bgcolor = bgcolor;
     }
@@ -37,13 +77,16 @@ impl Cell {
     /// Can include multiple unicode characters if combining characters are
     /// used, but will contain at most one character with a non-zero character
     /// width.
-    pub fn contents(&self) -> &str {
-        &self.contents
+    pub fn contents(&self) -> String {
+        self.contents
+            .iter()
+            .take(self.len as usize)
+            .collect::<String>()
     }
 
     /// Returns whether the cell contains any text data.
     pub fn has_contents(&self) -> bool {
-        self.contents != ""
+        self.len > 0
     }
 
     /// Returns whether the text data in the cell represents a wide character.
@@ -51,12 +94,11 @@ impl Cell {
         // strings in this context should always be an arbitrary character
         // followed by zero or more zero-width characters, so we should only
         // have to look at the first character
-        let width = self
-            .contents
-            .chars()
-            .next()
-            .map_or(0, |c| c.width().unwrap_or(0));
-        width > 1
+        if self.len == 0 {
+            false
+        } else {
+            self.contents[0].width().unwrap_or(0) > 1
+        }
     }
 
     pub(crate) fn attrs(&self) -> &crate::attrs::Attrs {
diff --git a/src/row.rs b/src/row.rs
index 4655f48..4511183 100644
--- a/src/row.rs
+++ b/src/row.rs
@@ -85,7 +85,7 @@ impl Row {
             if cell.has_contents() {
                 // using write! here is significantly slower, for some reason
                 // write!(contents, "{}", cell.contents()).unwrap();
-                contents.push_str(cell.contents());
+                contents.push_str(&cell.contents());
             } else {
                 contents.push(' ');
             }
diff --git a/tests/text.rs b/tests/text.rs
index 5c16039..e588a68 100644
--- a/tests/text.rs
+++ b/tests/text.rs
@@ -149,6 +149,14 @@ fn combining() {
     parser.process("\r\n\u{0301}".as_bytes());
     assert_eq!(parser.screen().cell(9, 79).unwrap().contents(), "a");
     assert_eq!(parser.screen().cell(10, 0).unwrap().contents(), "");
+
+    parser.process("\x1bcabcdefg\x1b[1;3H\u{0301}".as_bytes());
+    assert_eq!(parser.screen().contents(), "ab́cdefg");
+    parser.process("\x1b[1;2Hb\x1b[1;8H".as_bytes());
+    assert_eq!(parser.screen().contents(), "abcdefg");
+    let screen = parser.screen().clone();
+    parser.process(b"\x1bcabcdefg");
+    assert_eq!(parser.screen().contents_diff(&screen), b"\x1b[m");
 }
 
 #[test]
-- 
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