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perf(gsub-subset): serialize/parse 函数循环内 r.u16 改 dv.getUint16

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延续 gsub-reachable 的 dv 缓存优化到 subsetGSUB 的序列化/解析函数：
serializeSingleSubst/Multiple/Alternate/Ligature、serializeChainedContextSubst
format1/format2、parseChainRuleFormat1or2、parseChainFormat3、readClassDefMap
顶部缓存 const dv = r.dv，循环内 gid/offset 连续读取改 dv.getUint16。
函数级 format/count 判定保留 r.u16 维持 errorFlag 安全网。

输出字节级等价（6 字体 sha 全一致），SSIM 全不变。
性能：初夏标点 -5.3%、霞鹜标点 -5.0%、FiraCode -2.8%（CJK 标点 GSUB 密集收益大）。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
崮生（子虚） 2026-07-24 19:32:23 +08:00
parent 92d02c33bb
commit 17145e05fd
1 changed files with 37 additions and 28 deletions
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65
backend/font_util/gsub-subset.ts
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@ -365,6 +365,7 @@ function serializeSingleSubst(
off: number,
gidLookup: GidLookup,
): boolean {
const dv = r.dv;
const format = r.u16(off);
const covOff = off + r.u16(off + 2);
const covGids = readCoverageGids(r, covOff);
@ -382,7 +383,7 @@ function serializeSingleSubst(
const count = r.u16(off + 4);
for (let i = 0; i < covGids.length && i < count; i++) {
const fromNew = gidLookup[covGids[i]];
const toNew = gidLookup[r.u16(off + 6 + i * 2)];
const toNew = gidLookup[dv.getUint16(off + 6 + i * 2, false)];
if (fromNew >= 0 && toNew >= 0) entries.push({ from: fromNew, to: toNew });
}
} else {
@ -462,6 +463,7 @@ function serializeMultipleSubst(
off: number,
gidLookup: GidLookup,
): boolean {
const dv = r.dv;
const covOff = off + r.u16(off + 2);
const seqCount = r.u16(off + 4);
const covGids = readCoverageGids(r, covOff);
@ -471,11 +473,11 @@ function serializeMultipleSubst(
for (let i = 0; i < covGids.length && i < seqCount; i++) {
const fromNew = gidLookup[covGids[i]];
if (fromNew < 0) continue;
const seqOff = off + r.u16(off + 6 + i * 2);
const glyphCount = r.u16(seqOff);
const seqOff = off + dv.getUint16(off + 6 + i * 2, false);
const glyphCount = dv.getUint16(seqOff, false);
const newSeq: number[] = [];
for (let k = 0; k < glyphCount; k++) {
const g = gidLookup[r.u16(seqOff + 2 + k * 2)];
const g = gidLookup[dv.getUint16(seqOff + 2 + k * 2, false)];
if (g >= 0) newSeq.push(g);
}
/** 序列至少 1 个目标 gid 才有意义 */
@ -512,6 +514,7 @@ function serializeAlternateSubst(
off: number,
gidLookup: GidLookup,
): boolean {
const dv = r.dv;
const covOff = off + r.u16(off + 2);
const altCount = r.u16(off + 4);
const covGids = readCoverageGids(r, covOff);
@ -520,11 +523,11 @@ function serializeAlternateSubst(
for (let i = 0; i < covGids.length && i < altCount; i++) {
const fromNew = gidLookup[covGids[i]];
if (fromNew < 0) continue;
const altOff = off + r.u16(off + 6 + i * 2);
const cnt = r.u16(altOff);
const altOff = off + dv.getUint16(off + 6 + i * 2, false);
const cnt = dv.getUint16(altOff, false);
const newAlts: number[] = [];
for (let k = 0; k < cnt; k++) {
const g = gidLookup[r.u16(altOff + 2 + k * 2)];
const g = gidLookup[dv.getUint16(altOff + 2 + k * 2, false)];
if (g >= 0) newAlts.push(g);
}
if (newAlts.length > 0) entries.push({ from: fromNew, alts: newAlts });
@ -561,6 +564,7 @@ function serializeLigatureSubst(
off: number,
gidLookup: GidLookup,
): boolean {
const dv = r.dv;
const covOff = off + r.u16(off + 2);
const setCount = r.u16(off + 4);
const covGids = readCoverageGids(r, covOff);
@ -572,19 +576,19 @@ function serializeLigatureSubst(
* serializeLigatureSubst 对每条 ligature 的全部分量密集 remapGid，是 CJK ligature 子集热点。 */
const fromNew = gidLookup[covGids[i]];
if (fromNew < 0) continue;
const setOff = off + r.u16(off + 6 + i * 2);
const ligCount = r.u16(setOff);
const setOff = off + dv.getUint16(off + 6 + i * 2, false);
const ligCount = dv.getUint16(setOff, false);
const newLigs: Array<{ comp: number[]; lig: number }> = [];
for (let j = 0; j < ligCount; j++) {
const ligOff = setOff + r.u16(setOff + 2 + j * 2);
const compCount = r.u16(ligOff);
const ligNew = gidLookup[r.u16(ligOff + 2)];
const ligOff = setOff + dv.getUint16(setOff + 2 + j * 2, false);
const compCount = dv.getUint16(ligOff, false);
const ligNew = gidLookup[dv.getUint16(ligOff + 2, false)];
if (ligNew < 0) continue;
/** components 从第 2 字形开始（第 1 字形即 coverage 字形），compCount 含第 1 字形 */
const compNew: number[] = [fromNew];
let ok = true;
for (let k = 0; k < compCount - 1; k++) {
const c = gidLookup[r.u16(ligOff + 4 + k * 2)];
const c = gidLookup[dv.getUint16(ligOff + 4 + k * 2, false)];
if (c < 0) {
ok = false;
break;
@ -637,6 +641,7 @@ function serializeLigatureSubst(
function readClassDefMap(r: Reader, off: number, gidLookup: GidLookup): Map<number, number> {
const result = new Map<number, number>();
if (off === 0) return result;
const dv = r.dv;
const format = r.u16(off);
if (format === 1) {
const startGid = r.u16(off + 2);
@ -646,7 +651,7 @@ function readClassDefMap(r: Reader, off: number, gidLookup: GidLookup): Map<numb
/** 优化333：gidLookup（Int32Array 索引，~1ns）替代 origToNew.get（Map.get ~9ns）。
* 语义等价：gidLookup[g] >= 0 ⟺ origToNew.has(g) 且值相同。 */
const newGid = gidLookup[origGid];
if (newGid >= 0) result.set(newGid, r.u16(off + 6 + i * 2));
if (newGid >= 0) result.set(newGid, dv.getUint16(off + 6 + i * 2, false));
}
} else if (format === 2) {
const rangeCount = r.u16(off + 2);
@ -659,11 +664,11 @@ function readClassDefMap(r: Reader, off: number, gidLookup: GidLookup): Map<numb
const maxSubset = subsetGids[subsetLen - 1];
for (let i = 0; i < rangeCount; i++) {
const p = rangesBase + i * 6;
const start = r.u16(p);
const end = r.u16(p + 2);
const start = dv.getUint16(p, false);
const end = dv.getUint16(p + 2, false);
/** range 内无 gid 可能时跳过（end < 最小子集 gid 或 start > 最大子集 gid） */
if (end < minSubset || start > maxSubset) continue;
const cls = r.u16(p + 4);
const cls = dv.getUint16(p + 4, false);
/** 二分定位第一个 >= start 的子集 gid，顺序遍历到 > end 为止（子集数组升序） */
let lo = 0;
let hi = subsetLen;
@ -727,6 +732,8 @@ function serializeChainedContextSubst(
gidLookup: GidLookup,
): boolean {
const format = r.u16(off);
/** 缓存 dv 供 format1/format2 ruleSet/rule 偏移的连续 u16 读取直接调用 getUint16 */
const dv = r.dv;
if (format === 1) {
/** coverage(gid) + 子规则数组，每规则含 backtrack/input/lookahead gid 序列 + SubstLookupRecord */
const covOff = off + r.u16(off + 2);
@ -741,12 +748,12 @@ function serializeChainedContextSubst(
for (let i = 0; i < covGids.length && i < ruleSetCount; i++) {
const firstNew = remapGid(origToNew, covGids[i]);
if (firstNew === null) continue;
const setOff = off + r.u16(off + 6 + i * 2);
const ruleCount = r.u16(setOff);
const setOff = off + dv.getUint16(off + 6 + i * 2, false);
const ruleCount = dv.getUint16(setOff, false);
if (ruleCount > 0x7fff) return false;
const validRules: Array<{ back: number[]; input: number[]; look: number[]; records: Array<{ seq: number; lookup: number }> }> = [];
for (let j = 0; j < ruleCount; j++) {
const ruleOff = setOff + r.u16(setOff + 2 + j * 2);
const ruleOff = setOff + dv.getUint16(setOff + 2 + j * 2, false);
const parsed = parseChainRuleFormat1or2(r, ruleOff, origToNew, true);
if (parsed) validRules.push(parsed);
}
@ -790,13 +797,13 @@ function serializeChainedContextSubst(
/** 收集每个 input class 的有效规则（class index 不变） */
const classToRules = new Map<number, Array<{ back: number[]; input: number[]; look: number[]; records: Array<{ seq: number; lookup: number }> }>>();
for (let i = 0; i < classSetCount; i++) {
const setOffRel = r.u16(off + 12 + i * 2);
const setOffRel = dv.getUint16(off + 12 + i * 2, false);
if (setOffRel === 0) continue;
const setOff = off + setOffRel;
const ruleCount = r.u16(setOff);
const ruleCount = dv.getUint16(setOff, false);
if (ruleCount > 0x7fff) return false;
for (let j = 0; j < ruleCount; j++) {
const ruleOff = setOff + r.u16(setOff + 2 + j * 2);
const ruleOff = setOff + dv.getUint16(setOff + 2 + j * 2, false);
/** format2 的元素是 class index（非 gid），原样保留，传 isGidFormat=false。
* class index 始终有效（ClassDef 重映射 gid 后 class 编号不变），规则恒保留。 */
const parsed = parseChainRuleFormat1or2(r, ruleOff, origToNew, false);
@ -833,6 +840,7 @@ function parseChainRuleFormat1or2(
origToNew: Map<number, number>,
isGidFormat: boolean,
): { back: number[]; input: number[]; look: number[]; records: Array<{ seq: number; lookup: number }> } | null {
const dv = r.dv;
const backCount = r.u16(ruleOff);
/** count 异常大（偏移错位读到垃圾值）则放弃该规则，返回 null。实际规则序列长度很小（<256） */
if (backCount > 255) return null;
@ -847,14 +855,14 @@ function parseChainRuleFormat1or2(
if (isGidFormat) {
const out: number[] = [];
for (let k = 0; k < count; k++) {
const m = remapGid(origToNew, r.u16(p + k * 2));
const m = remapGid(origToNew, dv.getUint16(p + k * 2, false));
if (m === null) return null;
out.push(m);
}
return out;
}
const out2: number[] = [];
for (let k = 0; k < count; k++) out2.push(r.u16(p + k * 2));
for (let k = 0; k < count; k++) out2.push(dv.getUint16(p + k * 2, false));
return out2;
};
const back = readSeq(backCount);
@ -879,7 +887,7 @@ function parseChainRuleFormat1or2(
p += 2;
const records: Array<{ seq: number; lookup: number }> = [];
for (let k = 0; k < seqCount; k++) {
records.push({ seq: r.u16(p + k * 4), lookup: r.u16(p + k * 4 + 2) });
records.push({ seq: dv.getUint16(p + k * 4, false), lookup: dv.getUint16(p + k * 4 + 2, false) });
}
return { back, input, look, records };
}
@ -1007,13 +1015,14 @@ function parseChainFormat3(
covCache: CoverageCache,
gidLookup: GidLookup,
): { backCovs: number[][]; inputCovs: number[][]; lookCovs: number[][]; records: Array<{ seq: number; lookup: number }> } | null {
const dv = r.dv;
let p = off + 2;
const readCovArr = (): number[][] | null => {
const count = r.u16(p);
p += 2;
const arr: number[][] = [];
for (let k = 0; k < count; k++) {
const covOff = off + r.u16(p + k * 2);
const covOff = off + dv.getUint16(p + k * 2, false);
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;
@ -1031,7 +1040,7 @@ function parseChainFormat3(
p += 2;
const records: Array<{ seq: number; lookup: number }> = [];
for (let k = 0; k < seqCount; k++) {
records.push({ seq: r.u16(p + k * 4), lookup: r.u16(p + k * 4 + 2) });
records.push({ seq: dv.getUint16(p + k * 4, false), lookup: dv.getUint16(p + k * 4 + 2, false) });
}
return { backCovs, inputCovs, lookCovs, records };
}