JLNTV_IPD/web-font
4
0
Fork 0
mirror of https://github.com/2234839/web-font.git synced 2026-09-10 18:55:50 +08:00
Code Issues Projects Releases Wiki Activity

perf(loca): TypedArray 批量读+内联翻转替代 DataView 循环，loca 解析快 39%~46%

Browse Source 
loca 偏移是大端，原 DataView.getUint16/32 逐次调用含边界检查开销。改用
Uint16/32Array 直接 view 共享 buffer + 内联字节翻转，微基准实测：
- format0（Uint16）：157→84μs（-46%）
- format1（Uint32）：152→93μs（-39%）
（思源 30907 条 loca）

返回 Uint32Array 替代普通 Array，glyf.js 仅按下标 loca[index] 只读访问，
与 TypedArray 兼容（已确认 loca 仅被 glyf.js:22 读取、ttfreader.js:216 置 null）。

对齐保护：Uint16Array 需 2 字节对齐、Uint32Array 需 4 字节对齐，loca offset
来自表目录不保证对齐。检测 srcByteOff 对齐情况，未对齐回退 DataView 路径。

验证：基准测试 29 用例 SSIM 全部无回归；4 用例（思源千字文/标点/FiraCode/ttf）
sha256 输出字节逐字节等价。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
崮生（子虚） 2026-07-23 18:25:39 +08:00
parent 6f96e2b1dd
commit d793e22d92
1 changed files with 35 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
vendor/fonteditor-core/lib/ttf/table/loca.js vendored
View File

@ -15,21 +15,46 @@ var _default = exports.default = _table.default.create('loca', [], {
read: function read(reader, ttf) {
var offset = this.offset;
var indexToLocFormat = ttf.head.indexToLocFormat;
/* 优化7: 直接 view 批量读取，预分配数组 */
var numGlyphs = ttf.maxp.numGlyphs;
var wordOffset = new Array(numGlyphs);
/* 优化（TypedArray 批量读+内联翻转）：loca 偏移是大端，原 DataView.getUint16/32 逐次
* 调用有边界检查开销。改用 Uint16/32Array 直接 view 共享 buffer + 内联字节翻转，
* 实测 format0 快 46%、format1 快 39%（思源 30907 条 157→84μs / 152→93μs）。
* 返回 Uint32Array，glyf.js 仅按下标 `loca[index]` 只读访问，与 TypedArray 兼容。 */
var view = reader.view;
var srcByteOff = view.byteOffset + offset;
if (indexToLocFormat === 0) {
var vOffset = view.byteOffset + offset;
for (var i = 0; i < numGlyphs; i++) {
wordOffset[i] = view.getUint16(vOffset, false) * 2;
vOffset += 2;
if ((srcByteOff & 1) === 0) {
/* 优化（TypedArray 批量读+内联翻转）：offset 对齐 2 时用 Uint16Array view 共享 buffer，
* 避免 DataView.getUint16 逐次边界检查，实测快 46%。 */
var src16 = new Uint16Array(view.buffer, srcByteOff, numGlyphs);
var wordOffset = new Uint32Array(numGlyphs);
for (var i = 0; i < numGlyphs; i++) {
var v16 = src16[i];
wordOffset[i] = (((v16 >> 8) | (v16 << 8)) >>> 0 & 0xFFFF) * 2;
}
} else {
var wordOffset = new Uint32Array(numGlyphs);
var vOff0 = srcByteOff;
for (var i0 = 0; i0 < numGlyphs; i0++) {
wordOffset[i0] = view.getUint16(vOff0, false) * 2;
vOff0 += 2;
}
}
} else {
var vOffset2 = view.byteOffset + offset;
for (var j = 0; j < numGlyphs; j++) {
wordOffset[j] = view.getUint32(vOffset2, false);
vOffset2 += 4;
if ((srcByteOff & 3) === 0) {
var src32 = new Uint32Array(view.buffer, srcByteOff, numGlyphs);
var wordOffset = new Uint32Array(numGlyphs);
for (var j = 0; j < numGlyphs; j++) {
var v32 = src32[j];
wordOffset[j] = (v32 >>> 24) | ((v32 >> 8) & 0xFF00) | ((v32 << 8) & 0xFF0000) | (v32 << 24);
}
} else {
var wordOffset = new Uint32Array(numGlyphs);
var vOff1 = srcByteOff;
for (var j1 = 0; j1 < numGlyphs; j1++) {
wordOffset[j1] = view.getUint32(vOff1, false);
vOff1 += 4;
}
}
}
reader.offset = offset + (indexToLocFormat === 0 ? numGlyphs * 2 : numGlyphs * 4);