mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-11-02 07:43:42 +08:00
Chris Tate
975270cef5
Buffer.from(text, "base64" | "base64url") decoded each four-character group with four lookups and a sign test, then stored its three bytes one at a time. The decoder now first takes complete groups two at a time: each character's value comes from a table that holds it already shifted into place within its group's 24 bits, a single bit test covers all eight characters, and each group's three bytes go out in one four-byte store whose last byte the next store overwrites. A group with any other character (padding, whitespace, an invalid character) takes the previous path, and the two-group step resumes after it, so line-wrapped text keeps most of the gain. The destination already holds two spare bytes, which cover the extra store byte.
67 lines
2.2 KiB
TypeScript
67 lines
2.2 KiB
TypeScript
// Buffer.from(text, "base64" | "base64url") over complete eight-character
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// blocks and the text around them: every length from 0 to 40, an invalid
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// character at each position of a block, padding and text after it, both
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// alphabets, line breaks every 76 characters, sizes around the pool
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// threshold, and characters past U+00FF.
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let seed = 7;
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function next(): number {
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seed = (seed * 1103515245 + 12345) & 0x7fffffff;
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return seed >>> 8;
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}
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function bytes(size: number): Buffer {
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const buf = Buffer.alloc(size);
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for (let i = 0; i < size; i++) buf[i] = next() & 255;
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return buf;
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}
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const rows: string[] = [];
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for (let size = 0; size <= 30; size++) {
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const buf = bytes(size);
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const text = buf.toString("base64");
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const url = buf.toString("base64url");
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rows.push(
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`${size}:${text.length}:${Buffer.from(text, "base64").equals(buf)}:${Buffer.from(url, "base64url").equals(buf)}:${Buffer.from(url, "base64").equals(buf)}`,
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);
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}
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console.log(rows.join(" "));
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const block = Buffer.from("0123456789abcdefghijklmnopqrstuv").toString("base64");
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for (let at = 0; at < 16; at++) {
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for (const bad of [" ", "\n", "*", "=", "é", "中"]) {
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const text = block.slice(0, at) + bad + block.slice(at);
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console.log(at, JSON.stringify(bad), Buffer.from(text, "base64").toString("hex"));
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}
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}
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for (const text of [
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"QUJDREVGR0g=",
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"QUJDREVGR0",
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"QUJDREVGR0g=QUJD",
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"QUJD=REVGR0hJ",
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"QUJDREVGR0hJSktM",
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"QUJDREVGR0hJSktMTQ",
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"QUJDREVGR0hJSktMTQ==",
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"--__--__",
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"++//++//",
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"+-/_+-/_+-/_",
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"Q U J D R E V G R 0 h J",
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"QUJD\tREVG\r\nR0hJ",
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"=QUJDREVGR0hJ",
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"",
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]) {
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console.log(JSON.stringify(text), Buffer.from(text, "base64").toString("hex"), Buffer.from(text, "base64url").length);
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}
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for (const size of [4095, 4096, 4097, 6144, 6145, 70000]) {
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const buf = bytes(size);
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const text = buf.toString("base64");
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const wrapped = text.replace(/.{76}/g, "$&\n");
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const decoded = Buffer.from(text, "base64");
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const unwrapped = Buffer.from(wrapped, "base64");
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console.log(size, decoded.length, decoded.equals(buf), unwrapped.equals(buf), Buffer.byteLength(text, "base64"));
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}
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const wide = "QUJDREVGR0hJİSktM";
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console.log(Buffer.from(wide, "base64").toString("hex"), Buffer.from("ŁłQUJD", "base64").toString("hex"));
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