user: Demonstrate the C code that generates the assembly output below:

```asm
<clefiadoubleswap>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x30,%rsp
  mov    %rdi,-0x28(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x8(%rbp)
  xor    %eax,%eax
  mov    -0x28(%rbp),%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x7,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x1,%rax
  movzbl (%rax),%eax
  shr    %al
  or     %edx,%eax
  mov    %al,-0x20(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x1,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x7,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x2,%rax
  movzbl (%rax),%eax
  shr    %al
  or     %edx,%eax
  mov    %al,-0x1f(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x2,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x7,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x3,%rax
  movzbl (%rax),%eax
  shr    %al
  or     %edx,%eax
  mov    %al,-0x1e(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x3,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x7,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x4,%rax
  movzbl (%rax),%eax
  shr    %al
  or     %edx,%eax
  mov    %al,-0x1d(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x4,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x7,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x5,%rax
  movzbl (%rax),%eax
  shr    %al
  or     %edx,%eax
  mov    %al,-0x1c(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x5,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x7,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x6,%rax
  movzbl (%rax),%eax
  shr    %al
  or     %edx,%eax
  mov    %al,-0x1b(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x6,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x7,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x7,%rax
  movzbl (%rax),%eax
  shr    %al
  or     %edx,%eax
  mov    %al,-0x1a(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x7,%rax
  movzbl (%rax),%eax
  shl    $0x7,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0xf,%rax
  movzbl (%rax),%eax
  and    $0x7f,%eax
  or     %edx,%eax
  mov    %al,-0x19(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x8,%rax
  movzbl (%rax),%eax
  shr    $0x7,%al
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  movzbl (%rax),%eax
  and    $0xfffffffe,%eax
  or     %edx,%eax
  mov    %al,-0x18(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x9,%rax
  movzbl (%rax),%eax
  shr    $0x7,%al
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x8,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  add    %eax,%eax
  or     %edx,%eax
  mov    %al,-0x17(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0xa,%rax
  movzbl (%rax),%eax
  shr    $0x7,%al
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x9,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  add    %eax,%eax
  or     %edx,%eax
  mov    %al,-0x16(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0xb,%rax
  movzbl (%rax),%eax
  shr    $0x7,%al
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0xa,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  add    %eax,%eax
  or     %edx,%eax
  mov    %al,-0x15(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0xc,%rax
  movzbl (%rax),%eax
  shr    $0x7,%al
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0xb,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  add    %eax,%eax
  or     %edx,%eax
  mov    %al,-0x14(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0xd,%rax
  movzbl (%rax),%eax
  shr    $0x7,%al
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0xc,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  add    %eax,%eax
  or     %edx,%eax
  mov    %al,-0x13(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0xe,%rax
  movzbl (%rax),%eax
  shr    $0x7,%al
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0xd,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  add    %eax,%eax
  or     %edx,%eax
  mov    %al,-0x12(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0xf,%rax
  movzbl (%rax),%eax
  shr    $0x7,%al
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0xe,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  add    %eax,%eax
  or     %edx,%eax
  mov    %al,-0x11(%rbp)
  lea    -0x20(%rbp),%rcx
  mov    -0x28(%rbp),%rax
  mov    $0x10,%edx
  mov    %rcx,%rsi
  mov    %rax,%rdi
  call   <bytecpy@plt>
  nop
  mov    -0x8(%rbp),%rax
  sub    %fs:0x28,%rax
  je     L5
  call   <__stack_chk_fail@plt>
L5:
  leave
  ret
```

assistant: ```c
void clefiadoubleswap(unsigned char *lk) {
  unsigned char t[16];
  t[0] = (lk[0] << 7) | (lk[1] >> 1);
  t[1] = (lk[1] << 7) | (lk[2] >> 1);
  t[2] = (lk[2] << 7) | (lk[3] >> 1);
  t[3] = (lk[3] << 7) | (lk[4] >> 1);
  t[4] = (lk[4] << 7) | (lk[5] >> 1);
  t[5] = (lk[5] << 7) | (lk[6] >> 1);
  t[6] = (lk[6] << 7) | (lk[7] >> 1);
  t[7] = (lk[7] << 7) | (lk[15] & 0x7fu);
  t[8] = (lk[8] >> 7) | (lk[0] & 0xfeu);
  t[9] = (lk[9] >> 7) | (lk[8] << 1);
  t[10] = (lk[10] >> 7) | (lk[9] << 1);
  t[11] = (lk[11] >> 7) | (lk[10] << 1);
  t[12] = (lk[12] >> 7) | (lk[11] << 1);
  t[13] = (lk[13] >> 7) | (lk[12] << 1);
  t[14] = (lk[14] >> 7) | (lk[13] << 1);
  t[15] = (lk[15] >> 7) | (lk[14] << 1);
  bytecpy(lk, t, 16);
}
```