66 lines
1.5 KiB
Plaintext
66 lines
1.5 KiB
Plaintext
const alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
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const codes = new Uint8Array(256)
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for (let i = 0; i < alphabet.length; i++) {
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codes[alphabet.charCodeAt(i)] = i
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}
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codes[/* - */ 0x2d] = 62
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codes[/* _ */ 0x5f] = 63
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function byteLength (string) {
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let len = string.length
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if (string.charCodeAt(len - 1) === 0x3d) len--
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if (len > 1 && string.charCodeAt(len - 1) === 0x3d) len--
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return (len * 3) >>> 2
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}
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function toString (buffer) {
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const len = buffer.byteLength
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let result = ''
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for (let i = 0; i < len; i += 3) {
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result += (
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alphabet[buffer[i] >> 2] +
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alphabet[((buffer[i] & 3) << 4) | (buffer[i + 1] >> 4)] +
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alphabet[((buffer[i + 1] & 15) << 2) | (buffer[i + 2] >> 6)] +
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alphabet[buffer[i + 2] & 63]
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)
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}
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if (len % 3 === 2) {
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result = result.substring(0, result.length - 1) + '='
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} else if (len % 3 === 1) {
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result = result.substring(0, result.length - 2) + '=='
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}
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return result
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};
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function write (buffer, string, offset = 0, length = byteLength(string)) {
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const len = Math.min(length, buffer.byteLength - offset)
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for (let i = 0, j = 0; j < len; i += 4) {
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const a = codes[string.charCodeAt(i)]
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const b = codes[string.charCodeAt(i + 1)]
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const c = codes[string.charCodeAt(i + 2)]
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const d = codes[string.charCodeAt(i + 3)]
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buffer[j++] = (a << 2) | (b >> 4)
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buffer[j++] = ((b & 15) << 4) | (c >> 2)
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buffer[j++] = ((c & 3) << 6) | (d & 63)
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}
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return len
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};
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module.exports = {
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byteLength,
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toString,
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write
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}
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