user: 这段汇编代码用C语言表示是什么样的:

```asm
<getstr>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x28,%rsp
  mov    %rdx,0x8(%rsp)
  mov    %r8,0x18(%rsp)
  test   %rsi,%rsi
  sete   %al
  test   %rdx,%rdx
  sete   %dl
  or     %dl,%al
  jne    L86
  mov    %rdi,%r15
  mov    %rsi,%r14
  mov    %ecx,%ebx
  test   %rdi,%rdi
  je     L86
  cmpq   $0x0,(%rdi)
  je     L117
L159:
  mov    (%r14),%r12d
  mov    0x18(%rsp),%rax
  sub    %eax,%r12d
  add    (%r15),%rax
  mov    %rax,%r13
  movsbl %bl,%eax
  mov    %eax,0x14(%rsp)
  jmp    L116
L117:
  movq   $0x40,(%rsi)
  mov    $0x40,%edi
  call   <malloc@plt>
  mov    %rax,(%r15)
  test   %rax,%rax
  jne    L159
  mov    $0xffffffff,%eax
  jmp    L52
L157:
  movslq %ebx,%rbx
  sub    %rbx,%rax
  add    (%r14),%rax
  mov    %rax,%rbx
  mov    $0x1,%edi
  call   <assert@plt>
L75:
  mov    D0(%rip),%rax
  cmp    %ebp,(%rax)
  je     L8
  mov    0x8(%rsp),%rdi
  call   <ferror@plt>
  test   %rax,%rax
  jne    L8
  lea    0x1(%rbx),%r13
  mov    %bpl,(%rbx)
  sub    $0x1,%r12d
  cmp    %ebp,0x14(%rsp)
  je     L74
L116:
  mov    0x8(%rsp),%rdi
  call   <getc@plt>
  mov    %eax,%ebp
  movslq %r12d,%rdx
  mov    (%r14),%rax
  sub    %rdx,%rax
  mov    %r13,%rdx
  sub    (%r15),%rdx
  cmp    %rdx,%rax
  sete   %dil
  movzbl %dil,%edi
  call   <assert@plt>
  mov    %r13,%rbx
  cmp    $0x1,%r12d
  jg     L75
  mov    (%r14),%rax
  lea    (%rax,%rax,1),%rdx
  lea    0x40(%rax),%rsi
  cmp    $0x41,%rax
  cmovae %rdx,%rsi
  mov    %rsi,(%r14)
  mov    (%r15),%rdi
  lea    (%rdi,%rsi,1),%rax
  sub    %r13,%rax
  mov    %rax,%rbx
  mov    %eax,%r12d
  call   <realloc@plt>
  mov    %rax,(%r15)
  test   %rax,%rax
  jne    L157
  mov    $0xffffffff,%eax
  jmp    L52
L8:
  cmp    %rbx,(%r15)
  je     L47
L142:
  movb   $0x0,(%rbx)
  mov    0x18(%rsp),%rdx
  add    (%r15),%rdx
  mov    %ebx,%eax
  sub    %edx,%eax
L52:
  add    $0x28,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L74:
  mov    %r13,%rbx
  jmp    L142
L86:
  mov    $0xffffffff,%eax
  jmp    L52
L47:
  mov    $0xffffffff,%eax
  jmp    L52
```

assistant: ```c
int getstr(char **lineptr, size_t *n, FILE *stream, char terminator, size_t offset) {
  int nchars_avail;
  char *read_pos;
  int ret;
  if (!lineptr || !n || !stream)
    return -1;
  if (!*lineptr) {
    *n = 64;
    *lineptr = malloc(*n);
    if (!*lineptr)
      return -1;
  }
  nchars_avail = *n - offset;
  read_pos = *lineptr + offset;
  for (;;) {
    register int c = getc(stream);
    assert(*n - nchars_avail == read_pos - *lineptr);
    if (nchars_avail < 2) {
      if (*n > 64)
        *n *= 2;
      else
        *n += 64;
      nchars_avail = *n + *lineptr - read_pos;
      *lineptr = realloc(*lineptr, *n);
      if (!*lineptr)
        return -1;
      read_pos = *n - nchars_avail + *lineptr;
      assert(*n - nchars_avail == read_pos - *lineptr);
    }
    if (c == EOF || ferror(stream)) {
      if (read_pos == *lineptr)
        return -1;
      else
        break;
    }
    *read_pos++ = c;
    nchars_avail--;
    if (c == terminator)
      break;
  }
  *read_pos = '\0';
  ret = read_pos - (*lineptr + offset);
  return ret;
}
```