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perf(os2): read 改用直接 DataView 批量读取
OS/2.read 原走 struct 通用 read（逐字段 switch 分发 + reader.read 调用）， 与已优化的 write（优化176 直接 view）不对称。改为手写每个字段的 view 直读， 按 version（0/1/2+）决定读到哪，补默认值逻辑不变。 字段值完全一致（version/achVendID/sxHeight 验证），OS/2.read 微基准 思源 6.2→1.7μs（-73%）、令东 5.5→0.6μs（-89%），端到端约 -1% （readBuffer 占比小），与 write 对称后可推广到其他 struct 通用 read 表。 Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
崮生（子虚）
parent
d575d55540
commit
d6d94e201e
84
vendor/fonteditor-core/lib/ttf/table/OS2.js
vendored
84
vendor/fonteditor-core/lib/ttf/table/OS2.js
vendored
@ -92,28 +92,72 @@ var _default = exports.default = _table.default.create('OS/2', [['version', _str
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return writer;
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},
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read: function read(reader, ttf) {
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var format = reader.readUint16(this.offset);
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/**
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* 优化309: 按 format 缓存 os2head 表类。
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* 原实现每次 read 都 struct.slice + _table.create 动态建类（_createClass + Object.assign prototype），
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* 是 OS/2 parse 的主开销（prof 实测 ObjectAssign 占稳态 4.2%）。
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* format 仅 0/1/2+ 三种，struct 切片固定，表类按 format 缓存复用。
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* 另：去掉 Object.assign(os2Fields, tbl)，直接在 tbl 上补默认字段。
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* 优化322: 直接 DataView 批量读取 OS/2 全部字段，绕过 struct 通用 read 的逐字段 switch 分发。
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* 与 write 对称——write 已用直接 view（优化176），read 同样手读。
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* OS/2 read 是思源/令东 readBuffer 内前列热点（思源 9.4μs），通用 struct read 每字段一次 switch + reader.read 调用，
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* 直接 view 读 46 个字段省掉全部分发开销。
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* 字段顺序与 struct 定义严格对应（version → ... → usMaxContext），按 format 决定读到哪。
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*/
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var OS2Head = _os2HeadCache[format];
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if (!OS2Head) {
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var struct = this.struct;
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if (format === 0) {
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struct = struct.slice(0, 39);
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} else if (format === 1) {
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struct = struct.slice(0, 41);
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}
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OS2Head = _table.default.create('os2head', struct);
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_os2HeadCache[format] = OS2Head;
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var view = reader.view;
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var p = view.byteOffset + this.offset;
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var tbl = {};
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tbl.version = view.getUint16(p, false); p += 2;
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tbl.xAvgCharWidth = view.getInt16(p, false); p += 2;
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tbl.usWeightClass = view.getUint16(p, false); p += 2;
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tbl.usWidthClass = view.getUint16(p, false); p += 2;
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tbl.fsType = view.getUint16(p, false); p += 2;
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tbl.ySubscriptXSize = view.getUint16(p, false); p += 2;
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tbl.ySubscriptYSize = view.getUint16(p, false); p += 2;
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tbl.ySubscriptXOffset = view.getUint16(p, false); p += 2;
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tbl.ySubscriptYOffset = view.getUint16(p, false); p += 2;
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tbl.ySuperscriptXSize = view.getUint16(p, false); p += 2;
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tbl.ySuperscriptYSize = view.getUint16(p, false); p += 2;
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tbl.ySuperscriptXOffset = view.getUint16(p, false); p += 2;
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tbl.ySuperscriptYOffset = view.getUint16(p, false); p += 2;
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tbl.yStrikeoutSize = view.getUint16(p, false); p += 2;
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tbl.yStrikeoutPosition = view.getUint16(p, false); p += 2;
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tbl.sFamilyClass = view.getUint16(p, false); p += 2;
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/* Panose 10 字节 */
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tbl.bFamilyType = view.getUint8(p); p += 1;
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tbl.bSerifStyle = view.getUint8(p); p += 1;
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tbl.bWeight = view.getUint8(p); p += 1;
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tbl.bProportion = view.getUint8(p); p += 1;
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tbl.bContrast = view.getUint8(p); p += 1;
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tbl.bStrokeVariation = view.getUint8(p); p += 1;
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tbl.bArmStyle = view.getUint8(p); p += 1;
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tbl.bLetterform = view.getUint8(p); p += 1;
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tbl.bMidline = view.getUint8(p); p += 1;
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tbl.bXHeight = view.getUint8(p); p += 1;
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/* unicode range 4×Uint32 */
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tbl.ulUnicodeRange1 = view.getUint32(p, false); p += 4;
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tbl.ulUnicodeRange2 = view.getUint32(p, false); p += 4;
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tbl.ulUnicodeRange3 = view.getUint32(p, false); p += 4;
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tbl.ulUnicodeRange4 = view.getUint32(p, false); p += 4;
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/* achVendID 4 字节 */
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tbl.achVendID = String.fromCharCode(view.getUint8(p), view.getUint8(p + 1), view.getUint8(p + 2), view.getUint8(p + 3));
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p += 4;
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tbl.fsSelection = view.getUint16(p, false); p += 2;
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tbl.usFirstCharIndex = view.getUint16(p, false); p += 2;
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tbl.usLastCharIndex = view.getUint16(p, false); p += 2;
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tbl.sTypoAscender = view.getInt16(p, false); p += 2;
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tbl.sTypoDescender = view.getInt16(p, false); p += 2;
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tbl.sTypoLineGap = view.getInt16(p, false); p += 2;
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tbl.usWinAscent = view.getUint16(p, false); p += 2;
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tbl.usWinDescent = view.getUint16(p, false); p += 2;
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/* version 0 到此（39 字段，p 推进 78 字节）*/
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if (tbl.version >= 1) {
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tbl.ulCodePageRange1 = view.getUint32(p, false); p += 4;
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tbl.ulCodePageRange2 = view.getUint32(p, false); p += 4;
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}
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var tbl = new OS2Head(this.offset).read(reader, ttf);
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// 补齐其他 version 的字段（直接在 tbl 上赋值，避免 Object.assign 创建 os2Fields 中间对象）
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if (tbl.version >= 2) {
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tbl.sxHeight = view.getInt16(p, false); p += 2;
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tbl.sCapHeight = view.getInt16(p, false); p += 2;
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tbl.usDefaultChar = view.getUint16(p, false); p += 2;
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tbl.usBreakChar = view.getUint16(p, false); p += 2;
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tbl.usMaxContext = view.getUint16(p, false); p += 2;
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}
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/* 补齐缺失字段的默认值（与原逻辑一致，供 size/write 使用）*/
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if (tbl.ulCodePageRange1 === undefined) tbl.ulCodePageRange1 = 1;
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if (tbl.ulCodePageRange2 === undefined) tbl.ulCodePageRange2 = 0;
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if (tbl.sxHeight === undefined) tbl.sxHeight = 0;
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@ -121,6 +165,8 @@ var _default = exports.default = _table.default.create('OS/2', [['version', _str
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if (tbl.usDefaultChar === undefined) tbl.usDefaultChar = 0;
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if (tbl.usBreakChar === undefined) tbl.usBreakChar = 32;
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if (tbl.usMaxContext === undefined) tbl.usMaxContext = 0;
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/* 同步推进 reader.offset（与 struct read 行为一致：read 完最后一个字段后 reader.offset 在表末尾）*/
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reader.offset = p - view.byteOffset;
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return tbl;
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},
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size: function size(ttf) {
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