From eeba0993aa936219e0e0b1a3f2a15fe6acce7488 Mon Sep 17 00:00:00 2001
From: Antonio Scandurra <me@as-cii.com>
Date: Fri, 10 Dec 2021 09:16:58 +0100
Subject: [PATCH] Optimize anchor comparison and take full advantage of
 fragment IDs

---
 Cargo.lock                 |  1 +
 crates/text/Cargo.toml     |  1 +
 crates/text/src/anchor.rs  | 12 +++++++-----
 crates/text/src/locator.rs |  6 ++++++
 crates/text/src/text.rs    | 12 ++++--------
 5 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index a1188259ac..3c89563e3a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4853,6 +4853,7 @@ dependencies = [
  "ctor",
  "env_logger",
  "gpui",
+ "lazy_static",
  "log",
  "parking_lot",
  "rand 0.8.3",
diff --git a/crates/text/Cargo.toml b/crates/text/Cargo.toml
index 2b68a71a08..f4b7d7453f 100644
--- a/crates/text/Cargo.toml
+++ b/crates/text/Cargo.toml
@@ -15,6 +15,7 @@ collections = { path = "../collections" }
 sum_tree = { path = "../sum_tree" }
 anyhow = "1.0.38"
 arrayvec = "0.7.1"
+lazy_static = "1.4"
 log = "0.4"
 parking_lot = "0.11"
 rand = { version = "0.8.3", optional = true }
diff --git a/crates/text/src/anchor.rs b/crates/text/src/anchor.rs
index a781c9f887..85be47ad90 100644
--- a/crates/text/src/anchor.rs
+++ b/crates/text/src/anchor.rs
@@ -28,15 +28,17 @@ impl Anchor {
     }
 
     pub fn cmp<'a>(&self, other: &Anchor, buffer: &Snapshot) -> Result<Ordering> {
-        let offset_comparison = if self.timestamp == other.timestamp {
-            self.offset.cmp(&other.offset)
+        let fragment_id_comparison = if self.timestamp == other.timestamp {
+            Ordering::Equal
         } else {
             buffer
-                .full_offset_for_anchor(self)
-                .cmp(&buffer.full_offset_for_anchor(other))
+                .fragment_id_for_anchor(self)
+                .cmp(&buffer.fragment_id_for_anchor(other))
         };
 
-        Ok(offset_comparison.then_with(|| self.bias.cmp(&other.bias)))
+        Ok(fragment_id_comparison
+            .then_with(|| self.offset.cmp(&other.offset))
+            .then_with(|| self.bias.cmp(&other.bias)))
     }
 
     pub fn bias_left(&self, buffer: &Buffer) -> Anchor {
diff --git a/crates/text/src/locator.rs b/crates/text/src/locator.rs
index 249e79b6fd..e4feaf99ac 100644
--- a/crates/text/src/locator.rs
+++ b/crates/text/src/locator.rs
@@ -1,6 +1,12 @@
+use lazy_static::lazy_static;
 use smallvec::{smallvec, SmallVec};
 use std::iter;
 
+lazy_static! {
+    pub static ref MIN: Locator = Locator::min();
+    pub static ref MAX: Locator = Locator::max();
+}
+
 #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct Locator(SmallVec<[u64; 4]>);
 
diff --git a/crates/text/src/text.rs b/crates/text/src/text.rs
index d8c9c43d5f..6df4a67881 100644
--- a/crates/text/src/text.rs
+++ b/crates/text/src/text.rs
@@ -1763,12 +1763,11 @@ impl Snapshot {
         }
     }
 
-    fn full_offset_for_anchor(&self, anchor: &Anchor) -> FullOffset {
+    fn fragment_id_for_anchor(&self, anchor: &Anchor) -> &Locator {
         if *anchor == Anchor::min() {
-            Default::default()
+            &locator::MIN
         } else if *anchor == Anchor::max() {
-            let text = self.fragments.summary().text;
-            FullOffset(text.visible + text.deleted)
+            &locator::MAX
         } else {
             let anchor_key = InsertionFragmentKey {
                 timestamp: anchor.timestamp,
@@ -1790,10 +1789,7 @@ impl Snapshot {
             }
             let insertion = insertion_cursor.item().expect("invalid insertion");
             debug_assert_eq!(insertion.timestamp, anchor.timestamp, "invalid insertion");
-
-            let mut fragment_cursor = self.fragments.cursor::<(Option<&Locator>, FullOffset)>();
-            fragment_cursor.seek(&Some(&insertion.fragment_id), Bias::Left, &None);
-            fragment_cursor.start().1 + (anchor.offset - insertion.split_offset)
+            &insertion.fragment_id
         }
     }