src/vs/base/common/hash.ts/StringSHA1/_wrapUp
class StringSHA1:	private _wrapUp(): void {
		this._buff[this._buffLen++] = 0x80;
		fill(this._buff, this._buffLen);

		if (this._buffLen > 56) {
			this._step();
			fill(this._buff);
		}

		// this will fit because the mantissa can cover up to 52 bits
		const ml = 8 * this._totalLen;

		this._buffDV.setUint32(56, Math.floor(ml / 4294967296), false);
		this._buffDV.setUint32(60, ml % 4294967296, false);

		this._step();
	}