user: 提供的汇编代码用C语言表示会是什么样子：

```asm
<fd_readline>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x50,%rsp
  mov    %edi,-0x34(%rbp)
  mov    %esi,-0x38(%rbp)
  mov    %rdx,-0x40(%rbp)
  mov    %ecx,-0x44(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x8(%rbp)
  xor    %eax,%eax
  mov    -0x40(%rbp),%rax
  mov    %rax,-0x18(%rbp)
  mov    -0x44(%rbp),%eax
  cltq
  lea    -0x1(%rax),%rdx
  mov    -0x40(%rbp),%rax
  add    %rdx,%rax
  mov    %rax,-0x10(%rbp)
L85:
  lea    -0x21(%rbp),%rcx
  mov    -0x34(%rbp),%eax
  mov    $0x1,%edx
  mov    %rcx,%rsi
  mov    %eax,%edi
  call   <read@plt>
  mov    %eax,-0x1c(%rbp)
  cmpl   $0x0,-0x1c(%rbp)
  jg     L60
  subl   $0x1,-0x1c(%rbp)
  jmp    L73
L60:
  movzbl -0x21(%rbp),%eax
  movzbl %al,%eax
  cmp    $0x8,%eax
  je     L86
  cmp    $0xd,%eax
  je     L0
  jmp    L94
L86:
  mov    -0x18(%rbp),%rax
  cmp    -0x40(%rbp),%rax
  jbe    L128
  subq   $0x1,-0x18(%rbp)
  movzbl -0x21(%rbp),%eax
  movzbl %al,%eax
  mov    %eax,-0x20(%rbp)
  lea    -0x20(%rbp),%rcx
  mov    -0x38(%rbp),%eax
  mov    $0x1,%edx
  mov    %rcx,%rsi
  mov    %eax,%edi
  call   <write@plt>
  movl   $0x20,-0x20(%rbp)
  lea    -0x20(%rbp),%rcx
  mov    -0x38(%rbp),%eax
  mov    $0x1,%edx
  mov    %rcx,%rsi
  mov    %eax,%edi
  call   <write@plt>
  movzbl -0x21(%rbp),%eax
  movzbl %al,%eax
  mov    %eax,-0x20(%rbp)
  lea    -0x20(%rbp),%rcx
  mov    -0x38(%rbp),%eax
  mov    $0x1,%edx
  mov    %rcx,%rsi
  mov    %eax,%edi
  call   <write@plt>
  jmp    L2
L128:
  movl   $0x7,-0x20(%rbp)
  lea    -0x20(%rbp),%rcx
  mov    -0x38(%rbp),%eax
  mov    $0x1,%edx
  mov    %rcx,%rsi
  mov    %eax,%edi
  call   <write@plt>
  jmp    L2
L0:
  mov    -0x18(%rbp),%rax
  movb   $0x0,(%rax)
  mov    -0x18(%rbp),%rax
  sub    -0x40(%rbp),%rax
  mov    %eax,-0x1c(%rbp)
  jmp    L73
L94:
  mov    -0x18(%rbp),%rax
  cmp    -0x10(%rbp),%rax
  jae    L104
  mov    -0x18(%rbp),%rax
  lea    0x1(%rax),%rdx
  mov    %rdx,-0x18(%rbp)
  movzbl -0x21(%rbp),%edx
  mov    %dl,(%rax)
  movzbl -0x21(%rbp),%eax
  movzbl %al,%eax
  mov    %eax,-0x20(%rbp)
  lea    -0x20(%rbp),%rcx
  mov    -0x38(%rbp),%eax
  mov    $0x1,%edx
  mov    %rcx,%rsi
  mov    %eax,%edi
  call   <write@plt>
  jmp    L107
L104:
  movl   $0x7,-0x20(%rbp)
  lea    -0x20(%rbp),%rcx
  mov    -0x38(%rbp),%eax
  mov    $0x1,%edx
  mov    %rcx,%rsi
  mov    %eax,%edi
  call   <write@plt>
L107:
  nop
L2:
  jmp    L85
L73:
  mov    -0x1c(%rbp),%eax
  mov    -0x8(%rbp),%rdx
  sub    %fs:0x28,%rdx
  je     L68
  call   <__stack_chk_fail@plt>
L68:
  leave
  ret
```

assistant: ```c
int fd_readline(int fdi, int fdo, char *b, int bsz) {
  int r;
  unsigned char c;
  unsigned char *bp, *bpe;
  bp = b;
  bpe = b + bsz - 1;
  while (1) {
    r = read(fdi, &c, 1);
    if (r <= 0) {
      r--;
      goto out;
    }
    switch (c) {
    case '\b':
      if (bp > (unsigned char *)b) {
        bp--;
        do {
          int cl = c;
          write((fdo), &(cl), 1);
        } while (0);
        do {
          int cl = ' ';
          write((fdo), &(cl), 1);
        } while (0);
        do {
          int cl = c;
          write((fdo), &(cl), 1);
        } while (0);
      } else {
        do {
          int cl = '\x07';
          write((fdo), &(cl), 1);
        } while (0);
      }
      break;
    case '\r':
      *bp = '\0';
      r = bp - (unsigned char *)b;
      goto out;
    default:
      if (bp < bpe) {
        *bp++ = c;
        do {
          int cl = c;
          write((fdo), &(cl), 1);
        } while (0);
      } else {
        do {
          int cl = '\x07';
          write((fdo), &(cl), 1);
        } while (0);
      }
      break;
    }
  }
out:
  return r;
}
```