user: 请将这段汇编代码片段转换成等效的C代码:

```asm
<fromuutobits>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  push   %r12
  push   %rbx
  mov    %rdi,-0x28(%rbp)
  mov    %rsi,-0x30(%rbp)
  mov    -0x30(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x60,%al
  je     L252
  mov    -0x30(%rbp),%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  sub    $0x20,%eax
  jmp    L227
L252:
  mov    $0x0,%eax
L227:
  mov    %eax,-0x14(%rbp)
  addq   $0x1,-0x30(%rbp)
  cmpl   $0x0,-0x14(%rbp)
  js     L222
  cmpl   $0x2d,-0x14(%rbp)
  jle    L264
L222:
  mov    $0xfffffffe,%eax
  jmp    L48
L264:
  cmpl   $0x0,-0x14(%rbp)
  jne    L100
  mov    $0x0,%eax
  jmp    L48
L100:
  mov    -0x14(%rbp),%eax
  shl    $0x2,%eax
  add    $0x2,%eax
  movslq %eax,%rdx
  imul   $0x55555556,%rdx,%rdx
  shr    $0x20,%rdx
  sar    $0x1f,%eax
  mov    %eax,%ecx
  mov    %edx,%eax
  sub    %ecx,%eax
  mov    %eax,-0x18(%rbp)
  movl   $0x0,-0x1c(%rbp)
  jmp    L104
L207:
  mov    -0x30(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x60,%al
  je     L88
  mov    -0x30(%rbp),%rax
  movzbl (%rax),%eax
  sub    $0x20,%eax
  jmp    L85
L88:
  mov    $0x0,%eax
L85:
  mov    %eax,%ebx
  movzbl %bl,%eax
  and    $0xffffffc0,%eax
  test   %eax,%eax
  je     L254
  mov    $0xffffffff,%eax
  jmp    L48
L254:
  mov    -0x30(%rbp),%rax
  add    $0x1,%rax
  movzbl (%rax),%eax
  cmp    $0x60,%al
  je     L29
  mov    -0x30(%rbp),%rax
  add    $0x1,%rax
  movzbl (%rax),%eax
  sub    $0x20,%eax
  jmp    L6
L29:
  mov    $0x0,%eax
L6:
  mov    %eax,%r12d
  movzbl %r12b,%eax
  and    $0xffffffc0,%eax
  test   %eax,%eax
  je     L92
  mov    $0xffffffff,%eax
  jmp    L48
L92:
  movzbl %bl,%eax
  shl    $0x2,%eax
  mov    %eax,%esi
  mov    %r12d,%eax
  shr    $0x4,%al
  mov    %eax,%ecx
  mov    -0x1c(%rbp),%eax
  lea    0x1(%rax),%edx
  mov    %edx,-0x1c(%rbp)
  movslq %eax,%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  or     %ecx,%esi
  mov    %esi,%edx
  mov    %dl,(%rax)
  cmpl   $0x2,-0x18(%rbp)
  jle    L8
  mov    -0x30(%rbp),%rax
  add    $0x2,%rax
  movzbl (%rax),%eax
  cmp    $0x60,%al
  je     L245
  mov    -0x30(%rbp),%rax
  add    $0x2,%rax
  movzbl (%rax),%eax
  sub    $0x20,%eax
  jmp    L108
L245:
  mov    $0x0,%eax
L108:
  mov    %eax,%ebx
  movzbl %bl,%eax
  and    $0xffffffc0,%eax
  test   %eax,%eax
  je     L280
  mov    $0xffffffff,%eax
  jmp    L48
L280:
  movzbl %r12b,%eax
  shl    $0x4,%eax
  mov    %eax,%esi
  mov    %ebx,%eax
  shr    $0x2,%al
  mov    %eax,%ecx
  mov    -0x1c(%rbp),%eax
  lea    0x1(%rax),%edx
  mov    %edx,-0x1c(%rbp)
  movslq %eax,%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  or     %ecx,%esi
  mov    %esi,%edx
  mov    %dl,(%rax)
  cmpl   $0x3,-0x18(%rbp)
  jle    L8
  mov    -0x30(%rbp),%rax
  add    $0x3,%rax
  movzbl (%rax),%eax
  cmp    $0x60,%al
  je     L94
  mov    -0x30(%rbp),%rax
  add    $0x3,%rax
  movzbl (%rax),%eax
  sub    $0x20,%eax
  jmp    L275
L94:
  mov    $0x0,%eax
L275:
  mov    %eax,%r12d
  movzbl %r12b,%eax
  and    $0xffffffc0,%eax
  test   %eax,%eax
  je     L181
  mov    $0xffffffff,%eax
  jmp    L48
L181:
  movzbl %bl,%eax
  shl    $0x6,%eax
  mov    %eax,%esi
  mov    %r12d,%ecx
  mov    -0x1c(%rbp),%eax
  lea    0x1(%rax),%edx
  mov    %edx,-0x1c(%rbp)
  movslq %eax,%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  or     %ecx,%esi
  mov    %esi,%edx
  mov    %dl,(%rax)
L8:
  addq   $0x4,-0x30(%rbp)
  subl   $0x4,-0x18(%rbp)
L104:
  cmpl   $0x0,-0x18(%rbp)
  jg     L207
  mov    -0x1c(%rbp),%eax
  cmp    -0x14(%rbp),%eax
  jne    L213
  mov    -0x1c(%rbp),%eax
  jmp    L48
L213:
  mov    $0xfffffffd,%eax
L48:
  pop    %rbx
  pop    %r12
  pop    %rbp
  ret
```

assistant: ```c
int fromuutobits(char *out, const char *in) {
  int len, outlen, inlen;
  register unsigned char digit1, digit2;
  outlen = (in[0] == '`' ? 0 : in[0] - ' ');
  in += 1;
  if (outlen < 0 || outlen > 45)
    return -2;
  if (outlen == 0)
    return 0;
  inlen = (outlen * 4 + 2) / 3;
  len = 0;
  for (; inlen > 0; inlen -= 4) {
    digit1 = (in[0] == '`' ? 0 : in[0] - ' ');
    if ((digit1 & ~63))
      return -1;
    digit2 = (in[1] == '`' ? 0 : in[1] - ' ');
    if ((digit2 & ~63))
      return -1;
    out[len++] = (digit1 << 2) | (digit2 >> 4);
    if (inlen > 2) {
      digit1 = (in[2] == '`' ? 0 : in[2] - ' ');
      if ((digit1 & ~63))
        return -1;
      out[len++] = (digit2 << 4) | (digit1 >> 2);
      if (inlen > 3) {
        digit2 = (in[3] == '`' ? 0 : in[3] - ' ');
        if ((digit2 & ~63))
          return -1;
        out[len++] = (digit1 << 6) | digit2;
      }
    }
    in += 4;
  }
  return len == outlen ? len : -3;
}
```