38 lines
1.1 KiB
TypeScript
38 lines
1.1 KiB
TypeScript
const alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
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const inverse_alphabet =
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new Map<string, number>(Object.entries(alphabet).map(([i,c])=>[c,parseInt(i)]));
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export function vlqDecode(s: string): Array<number> {
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let acc = 0;
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let shift_amount = 0;
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const buf = [];
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for (const ch of s) {
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const sextet = inverse_alphabet.get(ch);
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acc |= (sextet & 0x1f) << shift_amount;
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shift_amount += 5;
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if (!(sextet & 0x20)) {
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const negative = !!(acc & 1);
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acc = acc >> 1;
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if (negative) acc = -acc;
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buf.push(acc);
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acc = 0;
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shift_amount = 0;
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}
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}
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return buf;
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}
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export function vlqEncode(ns: Array<number>): string {
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const buf = [];
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for (let n of ns) {
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n = (n < 0) ? ((-n) << 1) | 1 : (n << 1);
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do {
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const m = n & 0x1f;
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n = n >> 5;
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const sextet = (n > 0) ? m | 0x20 : m;
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buf.push(alphabet[sextet]);
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} while (n > 0);
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}
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return buf.join('');
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}
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