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perf(cff): rewriteCharstring/replaceDictOffsets 用 Uint8Array+写指针替代 number[]
rewriteCharstring(18.7%) 与 replaceDictOffsets(7.8%) 原 out/chunks: number[] 逐字节 push 有装箱开销 + new Uint8Array(out) 二次遍历 / Array.from+spread 多次拷贝。改预分配 Uint8Array + 写指针 wp（CALLSUBR 截断即 wp=stackStart[]），encodeDictInt 内联到写入处消除临时 number[]。 otf-思源8字 subsetOTF min 0.352→0.322ms(-9%)、p50 0.483→0.421ms(-13%)； otf-白狐5字 min 0.058→0.055ms。输出逐字节完全相同（19188B/26536B A/B 一致）。 Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
崮生（子虚）
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db33685475
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efe24d9312
@ -305,8 +305,18 @@ export function rewriteCharstring(
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newLocalCount: number,
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): Uint8Array {
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const newLocalBias = subrBias(newLocalCount);
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const out: number[] = [];
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/** 栈：记录每个 operand 在 out 中的起始位置（便于截断重写）。值为原始解析值。 */
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/**
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* 优化：预分配 Uint8Array + 写指针 wp 替代 number[] + push。
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* 原 out: number[] 逐字节 push 有装箱开销，且最终 new Uint8Array(out) 要二次遍历转换。
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* Uint8Array 直接写字节，wp 模拟 length（CALLSUBR 截断即 wp = stackStart[...]）。
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* 容量上界：(end-start) 是原始字节长度；CALLSUBR 重写时新 operand 编码（1~5 字节）
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* 可能比原 operand（1~5 字节）长，最坏每个 operand 多 4 字节。operand 数 ≤ end-start，
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* 故 (end-start)*2 + 16 是安全上界（远超实际，仅预分配不写入多余字节）。
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*/
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const cap = ((end - start) << 1) + 16;
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const out = new Uint8Array(cap);
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let wp = 0;
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/** 栈：记录每个 operand 在输出中的起始 wp（便于截断重写）。值为原始解析值。 */
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const stackStart: number[] = [];
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const stackVal: number[] = [];
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let stemCount = 0;
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@ -314,50 +324,57 @@ export function rewriteCharstring(
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while (p < end) {
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const b0 = b[p++];
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if (b0 === 255) {
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stackStart.push(out.length);
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stackStart.push(wp);
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stackVal.push(NaN);
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out.push(255, b[p], b[p + 1], b[p + 2], b[p + 3]);
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out[wp] = 255; out[wp + 1] = b[p]; out[wp + 2] = b[p + 1]; out[wp + 3] = b[p + 2]; out[wp + 4] = b[p + 3];
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wp += 5;
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p += 4;
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} else if (b0 === 28) {
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stackStart.push(out.length);
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stackStart.push(wp);
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stackVal.push(((b[p] << 24) | (b[p + 1] << 16)) >> 16);
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out.push(28, b[p], b[p + 1]);
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out[wp] = 28; out[wp + 1] = b[p]; out[wp + 2] = b[p + 1];
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wp += 3;
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p += 2;
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} else if (b0 === 29) {
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stackStart.push(out.length);
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stackStart.push(wp);
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stackVal.push(((b[p] << 24) | (b[p + 1] << 16) | (b[p + 2] << 8) | b[p + 3]) | 0);
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out.push(29, b[p], b[p + 1], b[p + 2], b[p + 3]);
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out[wp] = 29; out[wp + 1] = b[p]; out[wp + 2] = b[p + 1]; out[wp + 3] = b[p + 2]; out[wp + 4] = b[p + 3];
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wp += 5;
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p += 4;
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} else if (b0 >= 32 && b0 <= 246) {
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stackStart.push(out.length);
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stackStart.push(wp);
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stackVal.push(b0 - 139);
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out.push(b0);
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out[wp++] = b0;
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} else if (b0 >= 247 && b0 <= 250) {
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stackStart.push(out.length);
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stackStart.push(wp);
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stackVal.push((b0 - 247) * 256 + b[p] + 108);
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out.push(b0, b[p]);
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out[wp] = b0; out[wp + 1] = b[p];
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wp += 2;
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p += 1;
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} else if (b0 >= 251 && b0 <= 254) {
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stackStart.push(out.length);
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stackStart.push(wp);
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stackVal.push(-(b0 - 251) * 256 - b[p] - 108);
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out.push(b0, b[p]);
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out[wp] = b0; out[wp + 1] = b[p];
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wp += 2;
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p += 1;
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} else {
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/** 操作码 */
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if (b0 === 12) {
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out.push(12, b[p]);
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out[wp] = 12; out[wp + 1] = b[p];
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wp += 2;
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p += 1;
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stackStart.length = 0;
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stackVal.length = 0;
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} else if (b0 === T2_HSTEM || b0 === T2_VSTEM || b0 === T2_HSTEMHM || b0 === T2_VSTEMHM) {
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stemCount += stackVal.length >> 1;
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out.push(b0);
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out[wp++] = b0;
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stackStart.length = 0;
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stackVal.length = 0;
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} else if (b0 === T2_HINTMASK || b0 === T2_CNTRMASK) {
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out.push(b0);
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out[wp++] = b0;
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const maskBytes = (stemCount + 7) >>> 3;
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for (let i = 0; i < maskBytes; i++) out.push(b[p + i]);
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out.set(b.subarray(p, p + maskBytes), wp);
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wp += maskBytes;
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p += maskBytes;
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stackStart.length = 0;
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stackVal.length = 0;
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@ -367,31 +384,48 @@ export function rewriteCharstring(
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const newSn = localRemap.get(oldSn);
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if (newSn === undefined) {
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/** subr 未保留（理论上引用 charstring 必命中）——保留原 operand 保底 */
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out.push(T2_CALLSUBR);
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out[wp++] = T2_CALLSUBR;
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} else {
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/** 截断到栈顶 operand 起始，写入新编号编码 */
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out.length = stackStart[stackStart.length - 1];
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for (const eb of encodeDictInt(newSn - newLocalBias)) out.push(eb);
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out.push(T2_CALLSUBR);
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/** 截断到栈顶 operand 起始，写入新编号编码（直接写 Uint8Array，不分配临时数组） */
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wp = stackStart[stackStart.length - 1];
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const delta = newSn - newLocalBias;
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if (delta >= -107 && delta <= 107) {
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out[wp++] = delta + 139;
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} else if (delta >= 108 && delta <= 1131) {
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const v0 = delta - 108;
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out[wp] = 247 + (v0 >> 8); out[wp + 1] = v0 & 0xff;
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wp += 2;
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} else if (delta >= -1131 && delta <= -108) {
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const v0 = -delta - 108;
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out[wp] = 251 + (v0 >> 8); out[wp + 1] = v0 & 0xff;
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wp += 2;
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} else if (delta >= -32768 && delta <= 32767) {
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out[wp] = 28; out[wp + 1] = (delta >> 8) & 0xff; out[wp + 2] = delta & 0xff;
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wp += 3;
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} else {
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out[wp] = 29; out[wp + 1] = (delta >>> 24) & 0xff; out[wp + 2] = (delta >> 16) & 0xff; out[wp + 3] = (delta >> 8) & 0xff; out[wp + 4] = delta & 0xff;
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wp += 5;
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}
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out[wp++] = T2_CALLSUBR;
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}
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stackStart.length = 0;
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stackVal.length = 0;
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} else if (b0 === T2_CALLGSUBR) {
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/** global subr 不子集化：operand（调用编号）原样保留，bias 不变 */
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out.push(T2_CALLGSUBR);
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out[wp++] = T2_CALLGSUBR;
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stackStart.length = 0;
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stackVal.length = 0;
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} else if (b0 === T2_ENDCHAR) {
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out.push(b0);
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out[wp++] = b0;
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break;
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} else {
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out.push(b0);
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out[wp++] = b0;
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stackStart.length = 0;
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stackVal.length = 0;
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}
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}
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}
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return new Uint8Array(out);
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return out.subarray(0, wp);
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}
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/**
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@ -1082,8 +1116,15 @@ function encodeCharsetFormat0(cids: number[]): Uint8Array {
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* @param replacements 操作码键 → 新 offset 值
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*/
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function replaceDictOffsets(dictBytes: Uint8Array, replacements: Map<number, number>): Uint8Array {
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/** 先分段：按操作码切，重组 */
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const chunks: number[][] = [];
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/**
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* 优化：预分配 Uint8Array + 写指针 wp 替代 chunks: number[][] + Array.from + 二次拼接。
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* 原 chunks 方案每个操作码段分配一个 number[]（含 Array.from 拷贝 + spread 再拷贝），
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* 最后还要两轮遍历拼接。Uint8Array 直接顺序写入，零中间数组。
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* 容量上界：原 DICT 长度 + 每个替换 operand 最大 +4 字节（短编码→长编码）。
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*/
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const cap = dictBytes.length + replacements.size * 4 + 16;
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const out = new Uint8Array(cap);
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let wp = 0;
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let p = 0;
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let operandStart = 0;
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const len = dictBytes.length;
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@ -1093,17 +1134,35 @@ function replaceDictOffsets(dictBytes: Uint8Array, replacements: Map<number, num
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let op = b0;
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if (b0 === 12) op = (12 << 8) | dictBytes[p++];
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if (replacements.has(op)) {
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/** 替换：新操作数 + 操作码 */
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/** 替换：写入新编码操作数 + 操作码（内联 encodeDictInt 避免 number[] 分配） */
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const newVal = replacements.get(op)!;
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const encoded = encodeDictInt(newVal);
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if (op >= 256) {
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chunks.push([...encoded, 12, op & 0xff]);
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if (newVal >= -107 && newVal <= 107) {
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out[wp++] = newVal + 139;
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} else if (newVal >= 108 && newVal <= 1131) {
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const v0 = newVal - 108;
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out[wp] = 247 + (v0 >> 8); out[wp + 1] = v0 & 0xff;
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wp += 2;
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} else if (newVal >= -1131 && newVal <= -108) {
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const v0 = -newVal - 108;
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out[wp] = 251 + (v0 >> 8); out[wp + 1] = v0 & 0xff;
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wp += 2;
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} else if (newVal >= -32768 && newVal <= 32767) {
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out[wp] = 28; out[wp + 1] = (newVal >> 8) & 0xff; out[wp + 2] = newVal & 0xff;
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wp += 3;
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} else {
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chunks.push([...encoded, op]);
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out[wp] = 29; out[wp + 1] = (newVal >>> 24) & 0xff; out[wp + 2] = (newVal >> 16) & 0xff; out[wp + 3] = (newVal >> 8) & 0xff; out[wp + 4] = newVal & 0xff;
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wp += 5;
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}
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if (op >= 256) {
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out[wp] = 12; out[wp + 1] = op & 0xff;
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wp += 2;
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} else {
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out[wp++] = op;
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}
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} else {
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/** 保留原操作数 + 操作码 */
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chunks.push(Array.from(dictBytes.subarray(operandStart, p)));
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/** 保留原操作数 + 操作码（operandStart..p 原样拷贝） */
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out.set(dictBytes.subarray(operandStart, p), wp);
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wp += p - operandStart;
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}
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operandStart = p;
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} else if (b0 === 28) {
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@ -1122,13 +1181,5 @@ function replaceDictOffsets(dictBytes: Uint8Array, replacements: Map<number, num
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}
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/** 32~246 单字节，无后续 */
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}
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/** 拼接 */
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let total = 0;
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for (const c of chunks) total += c.length;
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const out = new Uint8Array(total);
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let off = 0;
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for (const c of chunks) {
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for (const v of c) out[off++] = v;
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}
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return out;
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return out.subarray(0, wp);
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}
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