code: function rl (cpu, n) {
      const cy = cpu.f >> 4 & 1;
      const r = n << 1 | cy;
  
      cpu.f = 0;
      if ((r & 0xff) == 0) cpu.f |= FLAG_Z;
      if ((n & 0x80) != 0) cpu.f |= FLAG_C;
  
      return r;
  }
docs: RL n
  
  Description:
  Rotate n left through Carry flag.
  
  Use with:
  n = A, B, C, D, E, H, L, (HL)
  
  Flags affected:
  Z - Set if result is zero.
  N - Reset.
  H - Reset.
  C - Contains old bit 7 data.
  
  Opcodes:
  Instruction    Parameters    Opcode    Cycles
  RL             A             CB 17     8
  RL             B             CB 10     8
  RL             C             CB 11     8
  RL             D             CB 12     8
  RL             E             CB 13     8
  RL             H             CB 14     8
  RL             L             CB 15     8
  RL             (HL)          CB 16     16