user: 请从给定的汇编指令推导出C源代码：

```asm
<getop>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x20,%rsp
  mov    %rdi,-0x18(%rbp)
  nop
L142:
  mov    $0x0,%eax
  call   <getch@plt>
  mov    %eax,-0x4(%rbp)
  mov    -0x4(%rbp),%eax
  mov    %eax,%edx
  mov    -0x18(%rbp),%rax
  mov    %dl,(%rax)
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x20,%al
  je     L142
  cmpl   $0x9,-0x4(%rbp)
  je     L142
  mov    -0x18(%rbp),%rax
  add    $0x1,%rax
  movb   $0x0,(%rax)
  cmpl   $0x2d,-0x4(%rbp)
  je     L90
  mov    -0x4(%rbp),%eax
  movsbl %al,%eax
  mov    %eax,%edi
  call   <isdigit@plt>
  test   %rax,%rax
  jne    L90
  cmpl   $0x2e,-0x4(%rbp)
  je     L90
  mov    -0x4(%rbp),%eax
  mov    %eax,%edi
  call   <isalpha@plt>
  test   %rax,%rax
  jne    L90
  mov    -0x4(%rbp),%eax
  jmp    L23
L90:
  movl   $0x0,-0x8(%rbp)
  mov    -0x4(%rbp),%eax
  mov    %eax,%edi
  call   <isalpha@plt>
  test   %rax,%rax
  je     L137
  jmp    L1
L79:
  mov    -0x8(%rbp),%eax
  lea    0x1(%rax),%edx
  mov    %edx,-0x8(%rbp)
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    -0x4(%rbp),%edx
  mov    %dl,(%rax)
  cmpl   $0xa,-0x4(%rbp)
  je     L135
  mov    $0x0,%eax
  call   <getch@plt>
  mov    %eax,-0x4(%rbp)
L1:
  mov    -0x4(%rbp),%eax
  mov    %eax,%edi
  call   <isalpha@plt>
  test   %rax,%rax
  jne    L79
  cmpl   $0xa,-0x4(%rbp)
  je     L79
  jmp    L48
L135:
  nop
L48:
  addl   $0x1,-0x8(%rbp)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movb   $0x0,(%rax)
  mov    $0x61,%eax
  jmp    L23
L137:
  cmpl   $0x2d,-0x4(%rbp)
  jne    L25
  mov    $0x0,%eax
  call   <getch@plt>
  mov    %eax,-0x4(%rbp)
  addl   $0x1,-0x8(%rbp)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    -0x4(%rbp),%edx
  mov    %dl,(%rax)
L25:
  mov    -0x4(%rbp),%eax
  movsbl %al,%eax
  mov    %eax,%edi
  call   <isdigit@plt>
  test   %rax,%rax
  je     L85
  nop
L10:
  mov    $0x0,%eax
  call   <getch@plt>
  mov    %eax,-0x4(%rbp)
  addl   $0x1,-0x8(%rbp)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    -0x4(%rbp),%edx
  mov    %dl,(%rax)
  movzbl (%rax),%eax
  movsbl %al,%eax
  mov    %eax,%edi
  call   <isdigit@plt>
  test   %rax,%rax
  jne    L10
L85:
  cmpl   $0x2e,-0x4(%rbp)
  jne    L204
  nop
L4:
  mov    $0x0,%eax
  call   <getch@plt>
  mov    %eax,-0x4(%rbp)
  addl   $0x1,-0x8(%rbp)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    -0x4(%rbp),%edx
  mov    %dl,(%rax)
  movzbl (%rax),%eax
  movsbl %al,%eax
  mov    %eax,%edi
  call   <isdigit@plt>
  test   %rax,%rax
  jne    L4
L204:
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movb   $0x0,(%rax)
  mov    D0(%rip),%rax
  mov    (%rax),%eax
  cmp    %eax,-0x4(%rbp)
  je     L30
  mov    -0x4(%rbp),%eax
  mov    %eax,%edi
  call   <ungetch@plt>
L30:
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x2d,%al
  jne    L17
  cmpl   $0x1,-0x8(%rbp)
  jne    L17
  mov    $0x2d,%eax
  jmp    L23
L17:
  mov    $0x30,%eax
L23:
  leave
  ret
```

assistant: ```c
int getop(char s[]) {
  int i, c;
  while ((s[0] = c = getch()) == ' ' || c == '\t') {
  }
  s[1] = '\0';
  if (c != '-' && !isdigit(c) && c != '.' && !isalpha(c)) {
    return c;
  }
  i = 0;
  if (isalpha(c)) {
    while (isalpha(c) || c == '\n') {
      s[i++] = c;
      if (c == '\n') {
        break;
      }
      c = getch();
    }
    s[++i] = '\0';
    return 'a';
  }
  if (c == '-') {
    s[++i] = c = getch();
  }
  if (isdigit(c)) {
    while (isdigit(s[++i] = c = getch())) {
    }
  }
  if (c == '.') {
    while (isdigit(s[++i] = c = getch())) {
    }
  }
  s[i] = '\0';
  if (c != EOF) {
    ungetch(c);
  }
  if (s[0] == '-' && i == 1) {
    return '-';
  }
  return '0';
}
```