user: 这段汇编代码用C语言表示是什么样的？

```asm
<ipv6_prefix_to_mask>:
  endbr64
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x10,%rsp
  mov    %fs:0x28,%rax
  mov    %rax,0x8(%rsp)
  xor    %eax,%eax
  cmp    $0x80,%edi
  ja     L295
  mov    %rsp,%r12
  mov    %edi,%ebx
  mov    %rsi,%rbp
  mov    $0x8,%edx
  xor    %esi,%esi
  mov    %r12,%rdi
  call   <memset@plt>
  mov    %ebx,%eax
  test   %ebx,%ebx
  je     L300
  mov    (%rsp),%rdx
  cmp    $0x7,%ebx
  jle    L130
  movl   $0xff,(%rdx)
  sub    $0x8,%eax
  je     L300
  lea    0x4(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x4(%rdx)
  sub    $0x10,%eax
  je     L300
  lea    0x8(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x8(%rdx)
  sub    $0x18,%eax
  je     L300
  lea    0xc(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0xc(%rdx)
  sub    $0x20,%eax
  je     L300
  lea    0x10(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x10(%rdx)
  sub    $0x28,%eax
  je     L300
  lea    0x14(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x14(%rdx)
  sub    $0x30,%eax
  je     L300
  lea    0x18(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x18(%rdx)
  sub    $0x38,%eax
  je     L300
  lea    0x1c(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x1c(%rdx)
  sub    $0x40,%eax
  je     L300
  lea    0x20(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x20(%rdx)
  sub    $0x48,%eax
  je     L300
  lea    0x24(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x24(%rdx)
  sub    $0x50,%eax
  je     L300
  lea    0x28(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x28(%rdx)
  sub    $0x58,%eax
  je     L300
  lea    0x2c(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x2c(%rdx)
  sub    $0x60,%eax
  je     L300
  lea    0x30(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x30(%rdx)
  sub    $0x68,%eax
  je     L300
  lea    0x34(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x34(%rdx)
  sub    $0x70,%eax
  je     L300
  lea    0x38(%rdx),%rcx
  cmp    $0x7,%eax
  jle    L359
  mov    %ebx,%eax
  movl   $0xff,0x38(%rdx)
  sub    $0x78,%eax
  je     L300
  lea    0x3c(%rdx),%rcx
  cmp    $0x8,%eax
  jne    L359
  movl   $0xff,0x3c(%rdx)
  jmp    L300
  nopl   0x0(%rax)
L359:
  mov    %rcx,%rdx
L130:
  mov    $0x8,%ecx
  sub    %eax,%ecx
  mov    $0xff,%eax
  shl    %cl,%eax
  mov    %eax,(%rdx)
L300:
  mov    $0x8,%edx
  mov    %r12,%rsi
  mov    %rbp,%rdi
  call   <memcpy@plt>
  xor    %eax,%eax
L263:
  mov    0x8(%rsp),%rdx
  sub    %fs:0x28,%rdx
  jne    L23
  add    $0x10,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  ret
L295:
  mov    $0xffffffff,%eax
  jmp    L263
L23:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
int ipv6_prefix_to_mask(unsigned prefix, struct in6_addr *mask) {
  struct in6_addr in6;
  int i, j;
  if (prefix > 128)
    return -1;
  memset(&in6, 0x0, sizeof(in6));
  for (i = prefix, j = 0; i > 0; i -= 8, j++) {
    if (i >= 8) {
      in6.s6_addr[j] = 0xff;
    } else {
      in6.s6_addr[j] = (unsigned long)(0xffU << (8 - i));
    }
  }
  memcpy(mask, &in6, sizeof(*mask));
  return 0;
}
```