user: 请从给定的汇编指令推导出C源代码:

```asm
<unpack>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  push   %r12
  push   %rbx
  mov    %rdi,%rbx
  mov    %rsi,%r12
  movzbl (%rbx),%eax
  movsbl %al,%eax
  shl    $0x5,%eax
  and    $0x1fe0,%eax
  mov    %eax,%edx
  lea    0x1(%rbx),%rax
  movzbl (%rax),%eax
  sar    $0x3,%al
  movsbl %al,%eax
  and    $0x1f,%eax
  or     %edx,%eax
  mov    %r12,%rsi
  mov    %eax,%edi
  mov    $0x0,%eax
  call   <conv@plt>
  add    $0x2,%r12
  add    $0x1,%rbx
  movzbl (%rbx),%eax
  movsbl %al,%eax
  shl    $0xa,%eax
  and    $0x1c00,%eax
  mov    %eax,%edx
  lea    0x1(%rbx),%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  shl    $0x2,%eax
  and    $0x3fc,%eax
  or     %eax,%edx
  lea    0x2(%rbx),%rax
  movzbl (%rax),%eax
  sar    $0x6,%al
  movsbl %al,%eax
  and    $0x3,%eax
  or     %edx,%eax
  mov    %r12,%rsi
  mov    %eax,%edi
  mov    $0x0,%eax
  call   <conv@plt>
  add    $0x2,%r12
  add    $0x2,%rbx
  movzbl (%rbx),%eax
  movsbl %al,%eax
  shl    $0x7,%eax
  and    $0x1f80,%eax
  mov    %eax,%edx
  lea    0x1(%rbx),%rax
  movzbl (%rax),%eax
  sar    %al
  movsbl %al,%eax
  and    $0x7f,%eax
  or     %edx,%eax
  mov    %r12,%rsi
  mov    %eax,%edi
  mov    $0x0,%eax
  call   <conv@plt>
  add    $0x2,%r12
  add    $0x1,%rbx
  movzbl (%rbx),%eax
  movsbl %al,%eax
  shl    $0xc,%eax
  and    $0x1000,%eax
  mov    %eax,%edx
  lea    0x1(%rbx),%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  shl    $0x4,%eax
  and    $0xff0,%eax
  or     %eax,%edx
  lea    0x2(%rbx),%rax
  movzbl (%rax),%eax
  sar    $0x4,%al
  movsbl %al,%eax
  and    $0xf,%eax
  or     %edx,%eax
  mov    %r12,%rsi
  mov    %eax,%edi
  mov    $0x0,%eax
  call   <conv@plt>
  add    $0x2,%r12
  add    $0x2,%rbx
  movzbl (%rbx),%eax
  movsbl %al,%eax
  shl    $0x9,%eax
  and    $0x1e00,%eax
  mov    %eax,%edx
  lea    0x1(%rbx),%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  add    %eax,%eax
  and    $0x1fe,%eax
  or     %eax,%edx
  lea    0x2(%rbx),%rax
  movzbl (%rax),%eax
  sar    $0x7,%al
  movsbl %al,%eax
  and    $0x1,%eax
  or     %edx,%eax
  mov    %r12,%rsi
  mov    %eax,%edi
  mov    $0x0,%eax
  call   <conv@plt>
  add    $0x2,%r12
  add    $0x2,%rbx
  movzbl (%rbx),%eax
  movsbl %al,%eax
  shl    $0x6,%eax
  and    $0x1fc0,%eax
  mov    %eax,%edx
  lea    0x1(%rbx),%rax
  movzbl (%rax),%eax
  sar    $0x2,%al
  movsbl %al,%eax
  and    $0x3f,%eax
  or     %edx,%eax
  mov    %r12,%rsi
  mov    %eax,%edi
  mov    $0x0,%eax
  call   <conv@plt>
  add    $0x2,%r12
  add    $0x1,%rbx
  movzbl (%rbx),%eax
  movsbl %al,%eax
  shl    $0xb,%eax
  and    $0x1800,%eax
  mov    %eax,%edx
  lea    0x1(%rbx),%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  shl    $0x3,%eax
  and    $0x7f8,%eax
  or     %eax,%edx
  lea    0x2(%rbx),%rax
  movzbl (%rax),%eax
  sar    $0x5,%al
  movsbl %al,%eax
  and    $0x7,%eax
  or     %edx,%eax
  mov    %r12,%rsi
  mov    %eax,%edi
  mov    $0x0,%eax
  call   <conv@plt>
  add    $0x2,%r12
  add    $0x2,%rbx
  movzbl (%rbx),%eax
  movsbl %al,%eax
  shl    $0x8,%eax
  and    $0x1f00,%eax
  mov    %eax,%edx
  lea    0x1(%rbx),%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  movzbl %al,%eax
  or     %edx,%eax
  mov    %r12,%rsi
  mov    %eax,%edi
  mov    $0x0,%eax
  call   <conv@plt>
  nop
  pop    %rbx
  pop    %r12
  pop    %rbp
  ret
```

assistant: ```c
void unpack(p, s) register char *p, *s;
{
  conv(p[0] << 5 & 017740 | p[1] >> 3 & 037, s);
  s += 2;
  p += 1;
  conv(p[0] << 10 & 016000 | p[1] << 2 & 01774 | p[2] >> 6 & 3, s);
  s += 2;
  p += 2;
  conv(p[0] << 7 & 017600 | p[1] >> 1 & 0177, s);
  s += 2;
  p += 1;
  conv(p[0] << 12 & 010000 | p[1] << 4 & 07760 | p[2] >> 4 & 017, s);
  s += 2;
  p += 2;
  conv(p[0] << 9 & 017000 | p[1] << 1 & 0776 | p[2] >> 7 & 01, s);
  s += 2;
  p += 2;
  conv(p[0] << 6 & 017700 | p[1] >> 2 & 077, s);
  s += 2;
  p += 1;
  conv(p[0] << 11 & 014000 | p[1] << 3 & 03770 | p[2] >> 5 & 07, s);
  s += 2;
  p += 2;
  conv(p[0] << 8 & 017400 | p[1] & 0377, s);
}
```