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perf(woff2): triplet 编码各分支内累加 gsbi，消除 TRIPLET_DATA_SIZES 查表

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令东千字文 woff2 write -12%（2.785→2.449ms），输出字节完全一致（cmp sha256 验证）。
原 gsbi += TRIPLET_DATA_SIZES[flag & 0x7F] 每点查表（Uint8Array 索引+位运算），
改为各 case 分支内 adv=1/1/1/2/3/4 常量累加，省掉查表。思源 -4%。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
崮生（子虚） 2026-07-24 11:48:12 +08:00
parent aeb2622a57
commit f945e1aedb
1 changed files with 11 additions and 9 deletions
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20
vendor/fonteditor-core/woff2/woff2-encode.js vendored
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@ -174,15 +174,9 @@ const sizeUIntBase128 = calcUIntBase128Size;
/* ======== Triplet 编码 ======== */
/**
* 从 triplet flag 推断数据字节数（避免重复计算）
* tripletIndex = flag & 0x7F
* 优化：预计算查找表，消除函数调用和条件分支
* 优化313: triplet flag → 数据字节数的映射已内联进 transformGlyfAndLoca 的各编码分支
* （字节数由分支确定：case1~3=1、case4=2、case5=3、case6=4），无需独立查表。
*/
const TRIPLET_DATA_SIZES = new Uint8Array(128);
for (let i = 0; i < 84; i++) TRIPLET_DATA_SIZES[i] = 1;
for (let i = 84; i < 120; i++) TRIPLET_DATA_SIZES[i] = 2;
for (let i = 120; i < 124; i++) TRIPLET_DATA_SIZES[i] = 3;
for (let i = 124; i < 128; i++) TRIPLET_DATA_SIZES[i] = 4;
/* ======== glyf + loca 表变换 ======== */
@ -522,12 +516,16 @@ function transformGlyfAndLoca(glyfData, locaData, indexFormat, numGlyphs) {
const absDy = dy < 0 ? -dy : dy;
const wpos = gsBase + gsbi;
let flag;
/** 优化313: 各分支内直接累加 gsbi（字节数由分支确定：1/1/1/2/3/4），消除 TRIPLET_DATA_SIZES 查表 */
let adv;
if (dx === 0 && absDy < 1280) {
_gs[wpos] = absDy & 0xFF;
flag = curveBit + ((absDy & 0xF00) >> 7) + (dy >= 0 ? 1 : 0);
adv = 1;
} else if (dy === 0 && dx !== 0 && absDx < 1280) {
_gs[wpos] = absDx & 0xFF;
flag = curveBit + 10 + ((absDx & 0xF00) >> 7) + (dx >= 0 ? 1 : 0);
adv = 1;
} else if (dx !== 0 && dy !== 0 && absDx < 65 && absDy < 65) {
const ax = absDx - 1;
const ay = absDy - 1;
@ -535,6 +533,7 @@ function transformGlyfAndLoca(glyfData, locaData, indexFormat, numGlyphs) {
const xSignBit = dx >= 0 ? 1 : 0;
const ySignBit = dy >= 0 ? 1 : 0;
flag = curveBit + 20 + (ax & 0x30) + ((ay & 0x30) >> 2) + xSignBit + 2 * ySignBit;
adv = 1;
} else if (dx !== 0 && dy !== 0 && absDx < 769 && absDy < 769) {
const ax = absDx - 1;
const ay = absDy - 1;
@ -543,6 +542,7 @@ function transformGlyfAndLoca(glyfData, locaData, indexFormat, numGlyphs) {
const xSignBit = dx >= 0 ? 1 : 0;
const ySignBit = dy >= 0 ? 1 : 0;
flag = curveBit + 84 + 12 * ((ax & 0x300) >> 8) + ((ay & 0x300) >> 6) + xSignBit + 2 * ySignBit;
adv = 2;
} else if (absDx < 4096 && absDy < 4096) {
_gs[wpos] = absDx >> 4;
_gs[wpos + 1] = ((absDx & 0xF) << 4) | (absDy >> 8);
@ -550,6 +550,7 @@ function transformGlyfAndLoca(glyfData, locaData, indexFormat, numGlyphs) {
const xSignBit = dx >= 0 ? 1 : 0;
const ySignBit = dy >= 0 ? 1 : 0;
flag = curveBit + 120 + xSignBit + 2 * ySignBit;
adv = 3;
} else {
_gs[wpos] = (absDx >> 8) & 0xFF;
_gs[wpos + 1] = absDx & 0xFF;
@ -558,10 +559,11 @@ function transformGlyfAndLoca(glyfData, locaData, indexFormat, numGlyphs) {
const xSignBit = dx >= 0 ? 1 : 0;
const ySignBit = dy >= 0 ? 1 : 0;
flag = curveBit + 124 + xSignBit + 2 * ySignBit;
adv = 4;
}
/** triplet flag 回写到 flagAccum（flagStream 存 triplet flag 而非原始 flag） */
_fa[_fwb + yi] = flag;
gsbi += TRIPLET_DATA_SIZES[flag & 0x7F];
gsbi += adv;
prevX = cx;
prevY = cy;
}