remove seg2 cache, fallback to binary search

Author: cometkim

README.md

@@ -215,7 +215,7 @@ 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) | Size (min+zstd) |
 |------------------------------|----------|------|----------:|-----------:|----------------:|--------------:|----------------:|
-| `unicode-segmenter/grapheme` |   16.0.0 |   ✔️ |    16,775 |     12,519 |           5,297 |         3,933 |           4,985 |
+| `unicode-segmenter/grapheme` |   16.0.0 |   ✔️ |    16,506 |     12,465 |           5,268 |         3,956 |           4,955 |
 | `graphemer`                  |   15.0.0 |   ✖️ ️|   410,435 |     95,104 |          15,752 |        10,660 |          15,911 |
 | `grapheme-splitter`          |   10.0.0 |   ✖️ |   122,254 |     23,682 |           7,852 |         4,802 |           6,753 |
 | `@formatjs/intl-segmenter`*  |   15.0.0 |   ✖️ |   603,510 |    369,673 |          72,273 |        49,530 |          68,027 |
@@ -231,7 +231,7 @@ Since [Hermes doesn't support the `Intl.Segmenter` API](https://github.com/faceb
 
 | Name                         | Bytecode size | Bytecode size (gzip)* |
 |------------------------------|--------------:|----------------------:|
-| `unicode-segmenter/grapheme` |        26,260 |                13,720 |
+| `unicode-segmenter/grapheme` |        26,075 |                13,630 |
 | `graphemer`                  |       134,089 |                31,766 |
 | `grapheme-splitter`          |        63,946 |                19,162 |
 

src/grapheme.js

@@ -208,34 +208,33 @@ const
 /**
  * Segmented lookup tables for BMP code points.
  *
- * Memory optimization: Skip regions that are almost 100% category 0 (Any):
- * - 0x3000-0x9FFF (CJK): 28,672 codepoints, only 12 non-Any -> inlined fast path
- * - 0xE000-0xFDFF (Private Use): 7,680 codepoints, only 1 non-Any -> inlined fast path
+ * Memory optimization: Skip regions that are almost 100% category {@link GC_Any}:
+ * - 0x3000-0x9FFF (CJK): 28,672 codepoints, only 12 non-Any ranges -> need to be inlined
+ * - 0xE000-0xFDFF (Private Use): 7,680 codepoints, only 1 non-Any range -> very rare, but quite simple to be inlined
+ * - 0xFE00-0xFFFF (Specials): 512 codepoints, only 5 ranges -> very rare, fall back to binary search
  *
  * Cache segments:
- * - seg0: 0x0080-0x2FFF (12,160 bytes)
- * - seg1: 0xA000-0xDFFF (16,384 bytes)
- * - seg2: 0xFE00-0xFFFF (512 bytes)
+ * - SEG0: 0x0080-0x2FFF (12,160 bytes)
+ * - SEG1: 0xA000-0xDFFF (16,384 bytes)
  *
- * Total: 29,056 bytes (~28KB)
+ * Total: 28,544 bytes (~28KB)
  */
-let seg0 = new Uint8Array(SEG0_MAX - SEG0_MIN + 1);
-let seg1 = new Uint8Array(SEG1_MAX - SEG1_MIN + 1);
-let seg2 = new Uint8Array(BMP_MAX - SEG2_MIN + 1);
-let bmpCursor = (() => {
+let SEG0 = new Uint8Array(SEG0_MAX - SEG0_MIN + 1);
+let SEG1 = new Uint8Array(SEG1_MAX - SEG1_MIN + 1);
+let SEG_CURSOR = (() => {
   let cursor = 0;
   while (cursor < grapheme_ranges.length) {
     let [start, end, cat] = grapheme_ranges[cursor];
-    if (start > BMP_MAX) break;
+    if (start > SEG1_MAX) break;
     cursor++;
 
     // Skip ranges outside segments (ASCII/CJK/PrivateUse fast paths)
-    if (end < SEG0_MIN || (start > SEG0_MAX && end < SEG1_MIN) || (start > SEG1_MAX && end < SEG2_MIN)) continue;
+    if (end < SEG0_MIN || (start > SEG0_MAX && end < SEG1_MIN)) continue;
 
-    for (let cp = start; cp <= end && cp <= BMP_MAX; cp++) {
-      if (cp >= SEG0_MIN && cp <= SEG0_MAX) seg0[cp - SEG0_MIN] = cat;
-      else if (cp >= SEG1_MIN && cp <= SEG1_MAX) seg1[cp - SEG1_MIN] = cat;
-      else if (cp >= SEG2_MIN) seg2[cp - SEG2_MIN] = cat;
+    for (let cp = start; cp <= end; cp++) {
+      if (cp >= SEG0_MIN && cp <= SEG0_MAX) SEG0[cp - SEG0_MIN] = cat;
+      else if (cp >= SEG1_MIN && cp <= SEG1_MAX) SEG1[cp - SEG1_MIN] = cat;
+      else continue;
     }
   }
   return cursor;
@@ -256,8 +255,7 @@ function cat(cp) {
   // 3. CJK fast path
   // 4. Segment 1 cache
   // 5. PrivateUse fast path
-  // 6. Segment 2 cache
-  // 7. Non-BMP binary search
+  // 7. Binary search
 
   // ASCII fast path
   if (cp < SEG0_MIN) {
@@ -268,7 +266,7 @@ function cat(cp) {
   }
   // Segment 0
   if (cp <= SEG0_MAX) {
-    return /** @type {GraphemeCategoryNum} */ (seg0[cp - SEG0_MIN]);
+    return /** @type {GraphemeCategoryNum} */ (SEG0[cp - SEG0_MIN]);
   }
   // CJK fast path
   if (cp < SEG1_MIN) {
@@ -282,18 +280,14 @@ function cat(cp) {
   }
   // Segment 1
   if (cp <= SEG1_MAX) {
-    return /** @type {GraphemeCategoryNum} */ (seg1[cp - SEG1_MIN]);
+    return /** @type {GraphemeCategoryNum} */ (SEG1[cp - SEG1_MIN]);
   }
   // Private Use fast path
   if (cp < SEG2_MIN) {
     return cp === 0xFB1E ? 3 : 0;
   }
-  // Segment 2
-  if (cp <= BMP_MAX) {
-    return /** @type {GraphemeCategoryNum} */ (seg2[cp - SEG2_MIN]);
-  }
   // Non-BMP
-  let idx = findUnicodeRangeIndex(cp, grapheme_ranges, bmpCursor);
+  let idx = findUnicodeRangeIndex(cp, grapheme_ranges, SEG_CURSOR);
   return idx < 0 ? 0 : grapheme_ranges[idx][2];
 }