mirror of
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perf(gsub): subsetGSUB 缓存+数组查找+裸读，FiraCode 983ms→30ms
FiraCode-代码用例(403 lookup)子集化从 983ms 降至 ~30ms，SSIM 全程保持 0.9923。
核心优化（CPU profile 逐层下钻）：
- coverage 解析+重映射缓存(off→{gids,remapped,outOfSubset})：format3 的 coverage
被多 subtable 引用，解析与重映射结果按 off 复用；readCoverageRemapped 边解析边过滤，
format3 不再分配中间原 gid 数组
- OTReader.dv 公开：coverage 偏移来自已验证 subtable，热循环用裸 DataView.getUint16
绕过 u16 的逐次边界检查
- GidLookup Int32Array(下标=原gid,值=新gid,-1=不在子集)替代 Map.get，coverage 过滤
的高频查询从哈希退化为数组索引
- OTWriter.rollback 改 pop：patches 按 pos 单调追加，回退从末尾 pop 替代全量 filter
(FiraCode 每次 rollback 392 次)
- gsub-reachable coverage 缓存：不动点迭代每轮重复解析同一 coverage，按 off 缓存
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
崮生（子虚）
parent
a84a4aa6f2
commit
28b6b1ebf4
@ -28,8 +28,17 @@ const LT_REVERSE_CHAIN = 5;
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const LT_CHAIN = 6;
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const LT_EXTENSION = 7;
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/** 读取 Coverage 表的 gid 列表 */
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function readCoverageGids(r: OTReader, off: number): number[] {
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/**
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* Coverage 解析缓存（off → 原 gid 数组）。
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* 不动点迭代每轮对全部 lookup 的 coverage 重复解析，但 coverage 字节不变故结果稳定。
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* 实测 FiraCode 迭代多轮，缓存消除绝大部分重复 u16 读取与数组分配（reachable 阶段主热点）。
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*/
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type CoverageCache = Map<number, number[]>;
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/** 读取 Coverage 表的 gid 列表。传入 cache 时按绝对偏移缓存解析结果。 */
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function readCoverageGids(r: OTReader, off: number, cache: CoverageCache): number[] {
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const hit = cache.get(off);
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if (hit !== undefined) return hit;
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const format = r.u16(off);
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const gids: number[] = [];
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if (format === 1) {
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@ -45,6 +54,7 @@ function readCoverageGids(r: OTReader, off: number): number[] {
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p += 6;
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}
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}
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cache.set(off, gids);
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return gids;
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}
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@ -61,6 +71,7 @@ export function collectReachableGsubTargets(
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): Set<number> {
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const dv = new DataView(gsubBytes.buffer, gsubBytes.byteOffset, gsubBytes.byteLength);
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const r = new OTReader(dv);
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const covCache: CoverageCache = new Map();
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const major = r.u16(0);
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const minor = r.u16(2);
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@ -120,7 +131,7 @@ export function collectReachableGsubTargets(
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/** type6：收集可触发规则引用的 lookup index 与所需 context gid */
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const refs = new Set<number>();
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const ctxGids = new Set<number>();
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collectChainRefs(r, subAbs, refs, ctxGids, inSubset);
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collectChainRefs(r, subAbs, refs, ctxGids, inSubset, covCache);
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for (const g of ctxGids) {
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if (!reachable.has(g)) { reachable.add(g); changed = true; }
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}
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@ -128,14 +139,14 @@ export function collectReachableGsubTargets(
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const refLk = lookups[li];
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if (!refLk) continue;
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for (const refSub of refLk.subtableAbsOffs) {
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const refTargets = collectSubtableTargets(r, refSub, refLk.effectiveType, inSubset);
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const refTargets = collectSubtableTargets(r, refSub, refLk.effectiveType, inSubset, covCache);
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for (const g of refTargets) {
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if (!reachable.has(g)) { reachable.add(g); changed = true; }
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}
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}
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}
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} else {
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const newTargets = collectSubtableTargets(r, subAbs, lk.effectiveType, inSubset);
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const newTargets = collectSubtableTargets(r, subAbs, lk.effectiveType, inSubset, covCache);
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for (const g of newTargets) {
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if (!reachable.has(g)) {
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reachable.add(g);
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@ -157,13 +168,14 @@ function collectSubtableTargets(
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off: number,
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type: number,
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inSubset: (gid: number) => boolean,
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covCache: CoverageCache,
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): number[] {
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const targets: number[] = [];
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if (type === LT_SINGLE) {
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/** SingleSubst: format1 coverage+delta / format2 coverage+gidArray */
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const format = r.u16(off);
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const covOff = off + r.u16(off + 2);
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const covGids = readCoverageGids(r, covOff);
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const covGids = readCoverageGids(r, covOff, covCache);
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if (format === 1) {
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const delta = r.i16(off + 4);
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for (const g of covGids) {
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@ -178,7 +190,7 @@ function collectSubtableTargets(
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} else if (type === LT_MULTIPLE) {
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const covOff = off + r.u16(off + 2);
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const seqCount = r.u16(off + 4);
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const covGids = readCoverageGids(r, covOff);
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const covGids = readCoverageGids(r, covOff, covCache);
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for (let i = 0; i < covGids.length && i < seqCount; i++) {
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if (!inSubset(covGids[i])) continue;
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const seqOff = off + r.u16(off + 6 + i * 2);
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@ -188,7 +200,7 @@ function collectSubtableTargets(
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} else if (type === LT_ALTERNATE) {
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const covOff = off + r.u16(off + 2);
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const altCount = r.u16(off + 4);
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const covGids = readCoverageGids(r, covOff);
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const covGids = readCoverageGids(r, covOff, covCache);
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for (let i = 0; i < covGids.length && i < altCount; i++) {
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if (!inSubset(covGids[i])) continue;
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const altOff = off + r.u16(off + 6 + i * 2);
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@ -199,7 +211,7 @@ function collectSubtableTargets(
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/** LigatureSubst: 全部 component 在子集 → target gid */
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const covOff = off + r.u16(off + 2);
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const setCount = r.u16(off + 4);
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const covGids = readCoverageGids(r, covOff);
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const covGids = readCoverageGids(r, covOff, covCache);
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for (let i = 0; i < covGids.length && i < setCount; i++) {
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const firstInSubset = inSubset(covGids[i]);
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const setOff = off + r.u16(off + 6 + i * 2);
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@ -244,12 +256,13 @@ function collectChainRefs(
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refs: Set<number>,
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contextGids: Set<number>,
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inSubset: (gid: number) => boolean,
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covCache: CoverageCache,
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): void {
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const format = r.u16(off);
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if (format === 1) {
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/** format1: coverage(gid) + SubRuleSet 数组，按 coverage gid 索引 */
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const covOff = off + r.u16(off + 2);
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const covGids = readCoverageGids(r, covOff);
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const covGids = readCoverageGids(r, covOff, covCache);
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const setCount = r.u16(off + 4);
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for (let i = 0; i < covGids.length && i < setCount; i++) {
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/** 第一分量（coverage gid）须在子集，否则该 SubRuleSet 不触发 */
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@ -287,7 +300,7 @@ function collectChainRefs(
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let triggerable = true;
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const readCovGids = (cnt: number): boolean => {
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for (let k = 0; k < cnt; k++) {
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const covGids = readCoverageGids(r, off + r.u16(p + k * 2));
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const covGids = readCoverageGids(r, off + r.u16(p + k * 2), covCache);
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for (const g of covGids) {
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allGids.push(g);
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if (!inSubset(g)) triggerable = false;
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@ -47,19 +47,68 @@ function remapGid(origToNew: Map<number, number>, gid: number): number | null {
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/** Coverage 表单个 range 展开为 gid 的上限保护：超出视为偏移错位读到垃圾数据。 */
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const COVERAGE_MAX_EXPAND = 0x10000;
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/** 读取 Coverage 表，返回覆盖的原 gid 列表（保持顺序）。 */
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function readCoverageGids(r: Reader, off: number): number[] {
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const format = r.u16(off);
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const gids: number[] = [];
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/**
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* Coverage 解析缓存（off → 解析条目）。
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* FiraCode 等 calt 字体的 ChainContextSubst format3 中，同一个 coverage 被大量 subtable
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* 重复引用（实测 604 次引用 / 83 个独立 coverage，最热 coverage 被引 126 次）。
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* 缓存「原 gid 解析」与「重映射后新 gid」两层结果，消除 ~86% 的重复 u16 读取、
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* map/filter 与数组分配（subsetGSUB 第一大 CPU+GC 热点）。
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* 生命周期与单次 subsetGSUB 调用绑定，origToNew 不变故结果稳定可复用。
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*/
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interface CoverageCacheEntry {
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/** 原 gid 列表（type1/2/3/4 按 index 配对用） */
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gids: number[];
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/** 重映射后新 gid 列表（format3 coverage 数组直接用），懒计算；null 表示尚未计算 */
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remapped: number[] | null;
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/** 原 coverage 非空但全部 gid 落子集外 → true，调用方据此判该 coverage 失效（区别于原本就空的合法 coverage） */
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outOfSubset: boolean;
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}
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type CoverageCache = Map<number, CoverageCacheEntry>;
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/**
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* 原gid → 新gid 的数组查找表（热路径专用）。
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* origToNew 是 Map<number,number>，每次 .get() 哈希查询开销大；coverage 解析对每个原 gid 都查一次，
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* 密度极高。构建 Int32Array 索引表（下标=原gid，值=新gid，-1 表示不在子集）后，查询退化为数组索引，
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* 比 Map.get 快数倍（subsetGSUB readCoverageRemapped 的主热点）。gid 上限 65536，表最大 256KB。
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*/
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type GidLookup = Int32Array;
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/** 读取 Coverage 表，返回覆盖的原 gid 列表（保持顺序）。
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* 传入 cache 时按 coverage 绝对偏移缓存解析结果（同一 off 复用同一数组实例）。
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* 热路径：coverage 偏移来自已验证的 subtable 结构（合法范围），直接用 dv.getUint16 绕过
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* u16 的逐次边界检查 + errorFlag 判定（subsetGSUB 第一大 CPU 热点，调用密度极高）。 */
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function readCoverageGids(r: Reader, off: number, cache?: CoverageCache): number[] {
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if (cache) {
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const hit = cache.get(off);
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if (hit !== undefined) return hit.gids;
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}
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const dv = r.dv;
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const len = dv.byteLength;
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/** coverage 偏移合法性兜底：越界则按错误处理（返回空，调用方降级） */
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if (off < 0 || off + 4 > len) {
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if (cache) cache.set(off, { gids: [], remapped: null, outOfSubset: false });
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return [];
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}
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const format = dv.getUint16(off, false);
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let gids: number[] = [];
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if (format === COV_LIST) {
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const count = r.u16(off + 2);
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for (let i = 0; i < count; i++) gids.push(r.u16(off + 4 + i * 2));
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const count = dv.getUint16(off + 2, false);
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const base = off + 4;
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if (base + count * 2 > len) {
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if (cache) cache.set(off, { gids: [], remapped: null, outOfSubset: false });
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return [];
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}
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/** 预分配 + 索引赋值，避免 push 动态扩容（format1 coverage 的高频热循环） */
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gids = new Array(count);
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for (let i = 0; i < count; i++) gids[i] = dv.getUint16(base + i * 2, false);
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} else if (format === COV_RANGE) {
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const rangeCount = r.u16(off + 2);
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const rangeCount = dv.getUint16(off + 2, false);
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let p = off + 4;
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for (let i = 0; i < rangeCount; i++) {
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const start = r.u16(p);
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const end = r.u16(p + 2);
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/** range 记录 6 字节，越界说明偏移错位读到垃圾 rangeCount，停止解析（返回已收集部分） */
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if (p + 6 > len) break;
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const start = dv.getUint16(p, false);
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const end = dv.getUint16(p + 2, false);
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/** 偏移错位会读到 end < start 或区间异常大的垃圾 range。
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* Coverage 的 gid 总数不可能超过字体 glyph 总数（< 0x10000），
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* 累计展开超出上限视为损坏数据，停止展开（返回已收集的部分，调用方按子集过滤，多余 gid 自然被丢弃）。 */
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@ -70,9 +119,73 @@ function readCoverageGids(r: Reader, off: number): number[] {
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p += 6;
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}
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}
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if (cache) cache.set(off, { gids, remapped: null, outOfSubset: false });
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return gids;
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}
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/**
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* 读取 coverage 并返回重映射后的新 gid 列表（带缓存）。
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* format3 的 coverage 不需要 index 配对（只需"子集内新 gid 集合"），故边解析边过滤，
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* 直接产出新 gid 数组、不分配中间的原 gid 数组（format3 是 subsetGSUB 最大热点，省一次完整数组分配）。
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* 解析+重映射结果按 off 缓存：同一 coverage 被多个 subtable 引用时只算一次。
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* @returns 重映射后新 gid 数组（保持顺序）；原 coverage 非空但全部 gid 落子集外时返回 null，
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* 调用方据此判该 coverage 失效。
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*/
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function readCoverageRemapped(
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r: Reader,
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off: number,
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gidLookup: GidLookup,
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cache: CoverageCache,
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): number[] | null {
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let entry = cache.get(off);
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if (entry !== undefined) {
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/** 已缓存：失效返回 null，否则返回重映射数组（remapped 已在首次计算时填好） */
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return entry.outOfSubset ? null : (entry.remapped as number[]);
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}
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const dv = r.dv;
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const len = dv.byteLength;
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/** 失效/空结果占位（首次计算后回填 cache） */
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let newGids: number[] = [];
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let origNonEmpty = false;
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let outOfSubset = false;
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if (off < 0 || off + 4 > len) {
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/** 越界，按空 coverage 处理 */
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} else {
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const format = dv.getUint16(off, false);
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if (format === COV_LIST) {
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const count = dv.getUint16(off + 2, false);
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const base = off + 4;
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if (base + count * 2 <= len) {
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origNonEmpty = count > 0;
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for (let i = 0; i < count; i++) {
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const m = gidLookup[dv.getUint16(base + i * 2, false)];
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if (m >= 0) newGids.push(m);
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}
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}
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} else if (format === COV_RANGE) {
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const rangeCount = dv.getUint16(off + 2, false);
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let p = off + 4;
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for (let i = 0; i < rangeCount; i++) {
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if (p + 6 > len) break;
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const start = dv.getUint16(p, false);
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const end = dv.getUint16(p + 2, false);
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if (end >= start && end - start < COVERAGE_MAX_EXPAND && newGids.length + (end - start + 1) <= COVERAGE_MAX_EXPAND) {
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for (let g = start; g <= end; g++) {
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origNonEmpty = true;
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const m = gidLookup[g];
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if (m >= 0) newGids.push(m);
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}
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}
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p += 6;
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}
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}
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}
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/** 原 coverage 非空但全部 gid 落子集外 → 失效（与原 coverage 本就空的合法空数组区分） */
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if (newGids.length === 0 && origNonEmpty) outOfSubset = true;
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cache.set(off, { gids: newGids, remapped: newGids, outOfSubset });
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return outOfSubset ? null : newGids;
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}
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/**
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* 从一组（子集内的）新 gid 序列写出 Coverage 表，返回其在 Writer 中的起始偏移。
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* 自动选择 format1（列表）或 format2（区间）中更紧凑的。
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@ -447,12 +560,14 @@ function serializeChainedContextSubst(
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r: Reader,
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off: number,
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origToNew: Map<number, number>,
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covCache: CoverageCache,
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gidLookup: GidLookup,
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): boolean {
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const format = r.u16(off);
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if (format === 1) {
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/** coverage(gid) + 子规则数组，每规则含 backtrack/input/lookahead gid 序列 + SubstLookupRecord */
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const covOff = off + r.u16(off + 2);
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const covGids = readCoverageGids(r, covOff);
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const covGids = readCoverageGids(r, covOff, covCache);
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const ruleSetCount = r.u16(off + 4);
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if (ruleSetCount > 0x7fff) return false;
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/** 按 coverage 字形收集有效规则 */
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@ -529,13 +644,13 @@ function serializeChainedContextSubst(
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}
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}
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if (classToRules.size === 0) return false;
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writeChainFormat2(w, r, coverageOff, backtrackCDOff, inputCDOff, lookaheadCDOff, origToNew, classToRules);
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writeChainFormat2(w, r, coverageOff, backtrackCDOff, inputCDOff, lookaheadCDOff, origToNew, classToRules, covCache, gidLookup);
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return true;
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}
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if (format === 3) {
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/** 显式 coverage 数组 + SubstLookupRecord */
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const parsed = parseChainFormat3(r, off, origToNew);
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const parsed = parseChainFormat3(r, off, covCache, gidLookup);
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if (!parsed) return false;
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writeChainFormat3(w, parsed);
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return true;
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@ -660,6 +775,8 @@ function writeChainFormat2(
|
||||
lookaheadCDOff: number,
|
||||
origToNew: Map<number, number>,
|
||||
classToRules: Map<number, Array<{ back: number[]; input: number[]; look: number[]; records: Array<{ seq: number; lookup: number }> }>>,
|
||||
covCache: CoverageCache,
|
||||
gidLookup: GidLookup,
|
||||
): void {
|
||||
const subStart = w.length;
|
||||
const coverageHolder: number[] = [0];
|
||||
@ -690,9 +807,10 @@ function writeChainFormat2(
|
||||
}
|
||||
}
|
||||
|
||||
/** Coverage 重映射：仅保留子集内 gid（input 第一分量必须在子集内才会被 shaping 命中） */
|
||||
const origCovGids = readCoverageGids(r, coverageOff);
|
||||
const newCovGids = origCovGids.map((g) => remapGid(origToNew, g)).filter((g): g is number => g !== null);
|
||||
/** Coverage 重映射：仅保留子集内 gid（input 第一分量必须在子集内才会被 shaping 命中）。
|
||||
* readCoverageRemapped 返回 null 表示原 coverage 非空但全子集外，此时 emitCoverage 写空 coverage
|
||||
* （与原 map/filter 后为空数组等价，浏览器匹配不命中，不影响其他规则）。 */
|
||||
const newCovGids = readCoverageRemapped(r, coverageOff, gidLookup, covCache) ?? [];
|
||||
coverageHolder[0] = emitCoverage(w, newCovGids);
|
||||
|
||||
/** 重映射三个 ClassDef 的 gid（class index 不变） */
|
||||
@ -721,7 +839,8 @@ function writeChainFormat2(
|
||||
function parseChainFormat3(
|
||||
r: Reader,
|
||||
off: number,
|
||||
origToNew: Map<number, number>,
|
||||
covCache: CoverageCache,
|
||||
gidLookup: GidLookup,
|
||||
): { backCovs: number[][]; inputCovs: number[][]; lookCovs: number[][]; records: Array<{ seq: number; lookup: number }> } | null {
|
||||
let p = off + 2;
|
||||
const readCovArr = (): number[][] | null => {
|
||||
@ -730,10 +849,9 @@ function parseChainFormat3(
|
||||
const arr: number[][] = [];
|
||||
for (let k = 0; k < count; k++) {
|
||||
const covOff = off + r.u16(p + k * 2);
|
||||
const gids = readCoverageGids(r, covOff);
|
||||
const newGids = gids.map((g) => remapGid(origToNew, g)).filter((g): g is number => g !== null);
|
||||
/** coverage 全部 gid 落在子集外，该 coverage 空 → 规则失效 */
|
||||
if (newGids.length === 0 && gids.length > 0) return null;
|
||||
const newGids = readCoverageRemapped(r, covOff, gidLookup, covCache);
|
||||
/** coverage 全部 gid 落在子集外（原非空）→ 规则失效 */
|
||||
if (newGids === null) return null;
|
||||
arr.push(newGids);
|
||||
}
|
||||
p += count * 2;
|
||||
@ -800,6 +918,8 @@ function serializeSubtable(
|
||||
off: number,
|
||||
type: number,
|
||||
origToNew: Map<number, number>,
|
||||
covCache: CoverageCache,
|
||||
gidLookup: GidLookup,
|
||||
): boolean {
|
||||
r.clearError();
|
||||
let ok: boolean;
|
||||
@ -817,7 +937,7 @@ function serializeSubtable(
|
||||
ok = serializeLigatureSubst(w, r, off, origToNew);
|
||||
break;
|
||||
case LT_CHAIN:
|
||||
ok = serializeChainedContextSubst(w, r, off, origToNew);
|
||||
ok = serializeChainedContextSubst(w, r, off, origToNew, covCache, gidLookup);
|
||||
break;
|
||||
default:
|
||||
return false;
|
||||
@ -841,6 +961,17 @@ export function subsetGSUB(
|
||||
const dv = new DataView(gsubBytes.buffer, gsubBytes.byteOffset, gsubBytes.byteLength);
|
||||
const r = new Reader(dv);
|
||||
|
||||
/** Coverage 解析缓存：ChainContextSubst format3 中 coverage 被大量 subtable 重复引用，
|
||||
* 按 off 缓存解析结果，消除重复 u16 读取与数组分配（FiraCode 实测 604 引用/83 独立 coverage）。 */
|
||||
const covCache: CoverageCache = new Map();
|
||||
|
||||
/** 原gid → 新gid 数组查找表（coverage 边解析边过滤的热路径用，数组索引比 Map.get 快数倍）。
|
||||
* 下标=原gid，值=新gid，-1 表示不在子集。容量覆盖出现的最大原 gid。 */
|
||||
let maxOrigGid = 0;
|
||||
for (const g of origToNew.keys()) if (g > maxOrigGid) maxOrigGid = g;
|
||||
const gidLookup: GidLookup = new Int32Array(maxOrigGid + 1).fill(-1);
|
||||
for (const [g, n] of origToNew) gidLookup[g] = n;
|
||||
|
||||
/** ---- GSUB Header ---- */
|
||||
const major = r.u16(0);
|
||||
const minor = r.u16(2);
|
||||
@ -971,7 +1102,7 @@ export function subsetGSUB(
|
||||
* 不再用 copyBytesBlock 按估算范围拷贝——原始 subtable 数据可能与其他 lookup 物理交错，
|
||||
* 按 lookup 边界估算会拷贝到错误字节（霞鹜文楷实测 subtable 在表头区之后）。 */
|
||||
const before = w.length;
|
||||
const ok = serializeSubtable(w, r, lk.subtableAbsOffs[j], lk.effectiveType, origToNew);
|
||||
const ok = serializeSubtable(w, r, lk.subtableAbsOffs[j], lk.effectiveType, origToNew, covCache, gidLookup);
|
||||
if (!ok) {
|
||||
w.rollback(before);
|
||||
writeEmptySubtable(w, lk.effectiveType);
|
||||
|
||||
@ -29,10 +29,13 @@ export class OTWriter {
|
||||
return this.bytes.length;
|
||||
}
|
||||
|
||||
/** 回退到指定字节位置，丢弃之后写入的字节与对应的偏移量槽（用于 subtable 重映射失败的保守降级） */
|
||||
/** 回退到指定字节位置，丢弃之后写入的字节与对应的偏移量槽（用于 subtable 重映射失败的保守降级）。
|
||||
* patches 按 pos 单调递增追加，故从尾部 pop 掉 pos >= 阈值的项即可，无需全量 filter
|
||||
* （subsetGSUB 每个失败的 subtable 都 rollback，FiraCode 实测 392 次/call，filter 改 pop 后此热点消失）。 */
|
||||
rollback(pos: number): void {
|
||||
this.bytes.length = pos;
|
||||
this.patches = this.patches.filter((p) => p.pos < pos);
|
||||
const patches = this.patches;
|
||||
while (patches.length > 0 && patches[patches.length - 1].pos >= pos) patches.pop();
|
||||
}
|
||||
|
||||
writeUint8(v: number): void {
|
||||
@ -83,7 +86,11 @@ export class OTWriter {
|
||||
*/
|
||||
export class OTReader {
|
||||
errorFlag = false;
|
||||
constructor(private dv: DataView) {}
|
||||
/** 原始 DataView，热路径（如 coverage 解析）可直接用 getUint16 绕过 u16 的逐次边界检查 */
|
||||
readonly dv: DataView;
|
||||
constructor(dv: DataView) {
|
||||
this.dv = dv;
|
||||
}
|
||||
|
||||
u16(off: number): number {
|
||||
if (off < 0 || off + 2 > this.dv.byteLength) {
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user