Optimize grapheme cluster boundary checking (#82)

Co-Authored-By: Claude <[email protected]>

Author: cometkim

.changeset/upset-mugs-fix.md

@@ -0,0 +1,5 @@
+---
+"unicode-segmenter": patch
+---
+
+Optimize grapheme cluster boundary checking.

README.md

@@ -256,7 +256,7 @@ Since [Hermes doesn't support the `Intl.Segmenter` API](https://github.com/faceb
 
 | Name                         | Unicode® | ESM? |   Size    | Size (min) | Size (min+gzip) | Size (min+br) |
 |------------------------------|----------|------|----------:|-----------:|----------------:|--------------:|
-| `unicode-segmenter/grapheme` |   16.0.0 |    ✔️ |    16,003 |     12,153 |           5,065 |         3,775 |
+| `unicode-segmenter/grapheme` |   16.0.0 |    ✔️ |    16,036 |     12,226 |           5,081 |         3,798 |
 | `graphemer`                  |   15.0.0 |    ✖️ ️|   410,435 |     95,104 |          15,752 |        10,660 |
 | `grapheme-splitter`          |   10.0.0 |    ✖️ |   122,252 |     23,680 |           7,852 |         4,841 |
 | `@formatjs/intl-segmenter`*  |   15.0.0 |    ✖️ |   603,285 |    369,560 |          72,218 |        49,416 |
@@ -272,7 +272,7 @@ Since [Hermes doesn't support the `Intl.Segmenter` API](https://github.com/faceb
 
 | Name                         | Bytecode size | Bytecode size (gzip)* |
 |------------------------------|--------------:|----------------------:|
-| `unicode-segmenter/grapheme` |        22,087 |                11,548 |
+| `unicode-segmenter/grapheme` |        22,002 |                11,468 |
 | `graphemer`                  |       133,978 |                31,713 |
 | `grapheme-splitter`          |        63,835 |                19,137 |
 

src/grapheme.js

@@ -296,58 +296,53 @@ function isBoundary(catBefore, catAfter, risCount, emoji, incb) {
     return true;
   }
 
-  // GB6
-  if (
-    catBefore === 5 &&
-    (catAfter === 5 || catAfter === 7 || catAfter === 8 || catAfter === 13)
-  ) {
+  // Most common cases - GB9, GB9a extend rules
+  if (catAfter === 3 || catAfter === 14 || catAfter === 11) {
     return false;
   }
 
-  // GB7
-  if (
-    (catBefore === 7 || catBefore === 13) &&
-    (catAfter === 12 || catAfter === 13)
-  ) {
-    return false;
-  }
-
-  // GB8
-  if (
-    catAfter === 12 &&
-    (catBefore === 8 || catBefore === 12)
-  ) {
-    return false;
-  }
+  // GB6 - L x (L | V | LV | LVT)
+  if (catBefore === 5) {
+    if (catAfter === 5 || catAfter === 7 || catAfter === 8 || catAfter === 13) {
+      return false;
+    }
 
-  // GB9
-  if (catAfter === 3 || catAfter === 14) {
-    return false;
-  }
+  } else {
+    // GB7 - (LV | V) x (V | T)
+    if (
+      (catBefore === 7 || catBefore === 13) &&
+      (catAfter === 13 || catAfter === 12)
+    ) {
+      return false;
+    }
 
-  // GB9a
-  if (catAfter === 11) {
-    return false;
-  }
+    // GB8 - (LVT | T) x T
+    if (
+      (catBefore === 8 || catBefore === 12) &&
+      catAfter === 12
+    ) {
+      return false;
+    }
 
-  // GB9b
-  if (catBefore === 9) {
-    return false;
-  }
+    // GB9b
+    if (catBefore === 9) {
+      return false;
+    }
 
-  // GB9c
-  if (catAfter === 0 && incb) {
-    return false;
-  }
+    // GB9c
+    if (catAfter === 0 && incb) {
+      return false;
+    }
 
-  // GB11
-  if (catBefore === 14 && catAfter === 4) {
-    return !emoji;
-  }
+    // GB11
+    if (catBefore === 14 && catAfter === 4) {
+      return !emoji;
+    }
 
-  // GB12, GB13
-  if (catBefore === 10 && catAfter === 10) {
-    return risCount % 2 === 0;
+    // GB12, GB13
+    if (catBefore === 10 && catAfter === 10) {
+      return risCount % 2 === 0;
+    }
   }
 
   // GB999