vlq.ts•1.39 kB
import type { StringReader, StringWriter } from './strings';
export const comma = ','.charCodeAt(0);
export const semicolon = ';'.charCodeAt(0);
const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
const intToChar = new Uint8Array(64); // 64 possible chars.
const charToInt = new Uint8Array(128); // z is 122 in ASCII
for (let i = 0; i < chars.length; i++) {
const c = chars.charCodeAt(i);
intToChar[i] = c;
charToInt[c] = i;
}
export function decodeInteger(reader: StringReader, relative: number): number {
let value = 0;
let shift = 0;
let integer = 0;
do {
const c = reader.next();
integer = charToInt[c];
value |= (integer & 31) << shift;
shift += 5;
} while (integer & 32);
const shouldNegate = value & 1;
value >>>= 1;
if (shouldNegate) {
value = -0x80000000 | -value;
}
return relative + value;
}
export function encodeInteger(builder: StringWriter, num: number, relative: number): number {
let delta = num - relative;
delta = delta < 0 ? (-delta << 1) | 1 : delta << 1;
do {
let clamped = delta & 0b011111;
delta >>>= 5;
if (delta > 0) clamped |= 0b100000;
builder.write(intToChar[clamped]);
} while (delta > 0);
return num;
}
export function hasMoreVlq(reader: StringReader, max: number) {
if (reader.pos >= max) return false;
return reader.peek() !== comma;
}