LZCNT - Count the Number of Leading Zero Bits

  # [source code]
  log2lzcnt:                # log2lzcnt({{.Requests}});  
      lzcnt   %rdi, %rdi  
      movq    $63,  %rax  
      sub     %rdi, %rax  
      ret                   # 2^{{.Log2lzcnt}} requests handled