From e8989c7fa45faca523284f0718376f145bd5d738 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=B4=AE=E7=94=9F=EF=BC=88=E5=AD=90=E8=99=9A=EF=BC=89?=
 <2234839456@qq.com>
Date: Sat, 25 Jul 2026 07:27:00 +0800
Subject: [PATCH] =?UTF-8?q?perf(cff):=20rewriteCharstring=20=E5=88=86?=
 =?UTF-8?q?=E6=94=AF=E6=8C=89=E7=83=AD=E5=BA=A6=E9=87=8D=E6=8E=92?=
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与 collectSubrRefs 同构的字节分派，operand（b0>=32）提前到首判定。思源千字文
subsetCFF 0.4920→0.4819ms（-2.1%），CFF 输出 sha 一致。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 backend/font_util/cff-subset.ts | 54 ++++++++++++++++++---------------
 1 file changed, 29 insertions(+), 25 deletions(-)

diff --git a/backend/font_util/cff-subset.ts b/backend/font_util/cff-subset.ts
index cb4a97b..48185bf 100644
--- a/backend/font_util/cff-subset.ts
+++ b/backend/font_util/cff-subset.ts
@@ -361,12 +361,35 @@ export function rewriteCharstring(
   let p = start;
   while (p < end) {
     const b0 = b[p++];
-    if (b0 === 255) {
-      lastStart = wp; lastVal = NaN;
-      out[wp] = 255; out[wp + 1] = b[p]; out[wp + 2] = b[p + 1]; out[wp + 3] = b[p + 2]; out[wp + 4] = b[p + 3];
-      wp += 5;
-      p += 4;
-      stackLen++;
+    /** 分支按热度重排：operand（b0>=32）占绝大多数字节，首判定（与 collectSubrRefs 同构）。 */
+    if (b0 >= 32) {
+      if (b0 <= 246) {
+        /** 单字节 operand，最热 */
+        lastStart = wp;
+        lastVal = b0 - 139;
+        out[wp++] = b0;
+        stackLen++;
+      } else if (b0 === 255) {
+        lastStart = wp; lastVal = NaN;
+        out[wp] = 255; out[wp + 1] = b[p]; out[wp + 2] = b[p + 1]; out[wp + 3] = b[p + 2]; out[wp + 4] = b[p + 3];
+        wp += 5;
+        p += 4;
+        stackLen++;
+      } else if (b0 <= 250) {
+        lastStart = wp;
+        lastVal = (b0 - 247) * 256 + b[p] + 108;
+        out[wp] = b0; out[wp + 1] = b[p];
+        wp += 2;
+        p += 1;
+        stackLen++;
+      } else {
+        lastStart = wp;
+        lastVal = -(b0 - 251) * 256 - b[p] - 108;
+        out[wp] = b0; out[wp + 1] = b[p];
+        wp += 2;
+        p += 1;
+        stackLen++;
+      }
     } else if (b0 === 28) {
       lastStart = wp;
       lastVal = ((b[p] << 24) | (b[p + 1] << 16)) >> 16;
@@ -381,25 +404,6 @@ export function rewriteCharstring(
       wp += 5;
       p += 4;
       stackLen++;
-    } else if (b0 >= 32 && b0 <= 246) {
-      lastStart = wp;
-      lastVal = b0 - 139;
-      out[wp++] = b0;
-      stackLen++;
-    } else if (b0 >= 247 && b0 <= 250) {
-      lastStart = wp;
-      lastVal = (b0 - 247) * 256 + b[p] + 108;
-      out[wp] = b0; out[wp + 1] = b[p];
-      wp += 2;
-      p += 1;
-      stackLen++;
-    } else if (b0 >= 251 && b0 <= 254) {
-      lastStart = wp;
-      lastVal = -(b0 - 251) * 256 - b[p] - 108;
-      out[wp] = b0; out[wp + 1] = b[p];
-      wp += 2;
-      p += 1;
-      stackLen++;
     } else {
       /** 操作码 */
       if (b0 === 12) {