user: 请从给定的汇编指令推导出C源代码：

```asm
<to8bit>:
  endbr64
  push   %rbp
  push   %rbx
  sub    $0x8,%rsp
L17:
  mov    $0x0,%eax
  call   <getchar@plt>
  cmp    $0x80,%eax
  je     L208
  movzbl %al,%edi
  cmp    $0x5c,%al
  je     L81
  call   <putchar@plt>
  jmp    L17
L81:
  mov    $0x0,%eax
  call   <getchar@plt>
  mov    %eax,%ebx
  cmp    $0x78,%eax
  je     L20
  jg     L177
  cmp    $0x37,%eax
  jg     L252
  cmp    $0x2f,%eax
  jle    L166
  sub    $0x30,%ebx
  mov    $0x0,%eax
  call   <getchar@plt>
  mov    %eax,%ebp
  lea    -0x30(%rax),%eax
  cmp    $0x7,%eax
  ja     L128
  shl    $0x3,%ebx
  mov    %eax,%ebp
  or     %ebx,%ebp
  mov    $0x0,%eax
  call   <getchar@plt>
  mov    %eax,%ebx
  lea    -0x30(%rax),%eax
  cmp    $0x7,%eax
  jbe    L100
  mov    %ebp,%edi
  call   <putchar@plt>
  mov    %ebx,%edi
  call   <putchar@plt>
  jmp    L17
L252:
  cmp    $0x58,%eax
  jne    L166
L20:
  mov    $0x0,%eax
  call   <getchar@plt>
  mov    %eax,%ebp
  lea    -0x30(%rax),%eax
  cmp    $0x9,%eax
  ja     L62
  mov    %eax,%ebp
L265:
  mov    $0x0,%eax
  call   <getchar@plt>
  mov    %eax,%ebx
  lea    -0x30(%rax),%eax
  cmp    $0x9,%eax
  ja     L64
  shl    $0x4,%ebp
  mov    %eax,%edi
  or     %ebp,%edi
L233:
  call   <putchar@plt>
  jmp    L17
L177:
  cmp    $0x80,%eax
  jne    L166
  mov    $0x5c,%edi
  call   <putchar@plt>
L208:
  add    $0x8,%rsp
  pop    %rbx
  pop    %rbp
  ret
L62:
  lea    -0x61(%rbp),%eax
  cmp    $0x5,%eax
  ja     L150
  sub    $0x57,%ebp
  jmp    L265
L150:
  lea    -0x41(%rbp),%eax
  cmp    $0x5,%eax
  ja     L147
  sub    $0x37,%ebp
  jmp    L265
L147:
  mov    $0x5c,%edi
  call   <putchar@plt>
  mov    %ebx,%edi
  call   <putchar@plt>
  mov    %ebp,%edi
  call   <putchar@plt>
  jmp    L17
L64:
  lea    -0x61(%rbx),%eax
  cmp    $0x5,%eax
  ja     L221
  shl    $0x4,%ebx
  lea    -0x57(%rbx),%edi
  jmp    L233
L221:
  lea    -0x41(%rbx),%eax
  cmp    $0x5,%eax
  ja     L59
  shl    $0x4,%ebx
  lea    -0x37(%rbx),%edi
  jmp    L233
L59:
  mov    %ebp,%edi
  call   <putchar@plt>
  mov    %ebx,%edi
  call   <putchar@plt>
  jmp    L17
L128:
  mov    %ebx,%edi
  call   <putchar@plt>
  mov    %ebp,%edi
  call   <putchar@plt>
  jmp    L17
L100:
  shl    $0x3,%ebp
  lea    -0x30(%rbx),%edi
  or     %ebp,%edi
  call   <putchar@plt>
  jmp    L17
L166:
  mov    $0x5c,%edi
  call   <putchar@plt>
  mov    %ebx,%edi
  call   <putchar@plt>
  jmp    L17
```

assistant: ```c
void to8bit() {
  int backch;
  int ch;
  while ((ch = getchar()) != EOF) {
    ch &= 0xFF;
    if (ch != '\\')
      (void)putchar(ch);
    else {
      ch = getchar();
      switch (ch) {
      case EOF:
        (void)putchar('\\');
        return;
      case 'x':
      case 'X':
        backch = ch;
        ch = getchar();
        if (ch >= '0' && ch <= '9')
          backch = ch - '0';
        else if (ch >= 'a' && ch <= 'f')
          backch = ch - 'a' + 0xA;
        else if (ch >= 'A' && ch <= 'F')
          backch = ch - 'A' + 0xA;
        else {
          (void)putchar('\\');
          (void)putchar(backch);
          (void)putchar(ch);
          break;
        }
        ch = getchar();
        if (ch >= '0' && ch <= '9')
          backch = (backch << 4) | (ch - '0');
        else if (ch >= 'a' && ch <= 'f')
          backch = (ch << 4) - 'a' + 0xA;
        else if (ch >= 'A' && ch <= 'F')
          backch = (ch << 4) - 'A' + 0xA;
        else {
          (void)putchar(backch);
          (void)putchar(ch);
          break;
        }
        (void)putchar(backch);
        break;
      case '0':
      case '1':
      case '2':
      case '3':
      case '4':
      case '5':
      case '6':
      case '7':
        backch = ch - '0';
        ch = getchar();
        if (ch >= '0' && ch <= '7')
          backch = (backch << 3) | (ch - '0');
        else {
          (void)putchar(backch);
          (void)putchar(ch);
          break;
        }
        ch = getchar();
        if (ch >= '0' && ch <= '7')
          backch = (backch << 3) | (ch - '0');
        else {
          (void)putchar(backch);
          (void)putchar(ch);
          break;
        }
        (void)putchar(backch);
        break;
        break;
      default:
        (void)putchar('\\');
        (void)putchar(ch);
        break;
      }
    }
  }
}
```