user: 下面的汇编指令对应的C源代码是什么：

```asm
<decode_block>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x30,%rsp
  mov    %rdi,-0x28(%rbp)
  mov    %rsi,-0x30(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x8(%rbp)
  xor    %eax,%eax
  mov    -0x28(%rbp),%rax
  mov    %rax,-0x18(%rbp)
  movl   $0x0,-0x20(%rbp)
  movl   $0x0,-0x1c(%rbp)
  movl   $0x0,-0xc(%rbp)
  jmp    L34
L22:
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x20,%al
  je     L6
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x2b,%al
  jne    L30
  mov    -0x20(%rbp),%eax
  cltq
  movb   $0x3e,-0xc(%rbp,%rax,1)
  jmp    L197
L30:
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x2f,%al
  jne    L102
  mov    -0x20(%rbp),%eax
  cltq
  movb   $0x3f,-0xc(%rbp,%rax,1)
  jmp    L197
L102:
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x3d,%al
  jne    L50
  mov    -0x20(%rbp),%eax
  cltq
  movb   $0x0,-0xc(%rbp,%rax,1)
  jmp    L197
L50:
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x2f,%al
  jbe    L135
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x39,%al
  ja     L135
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  add    $0x4,%eax
  mov    %eax,%edx
  mov    -0x20(%rbp),%eax
  cltq
  mov    %dl,-0xc(%rbp,%rax,1)
  jmp    L197
L135:
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x40,%al
  jbe    L201
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x5a,%al
  ja     L201
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  sub    $0x41,%eax
  mov    %eax,%edx
  mov    -0x20(%rbp),%eax
  cltq
  mov    %dl,-0xc(%rbp,%rax,1)
  jmp    L197
L201:
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x60,%al
  jbe    L67
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x7a,%al
  ja     L67
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  sub    $0x47,%eax
  mov    %eax,%edx
  mov    -0x20(%rbp),%eax
  cltq
  mov    %dl,-0xc(%rbp,%rax,1)
  jmp    L197
L67:
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x20,%al
  jne    L162
  addl   $0x1,-0x1c(%rbp)
L197:
  addl   $0x1,-0x20(%rbp)
L6:
  addl   $0x1,-0x1c(%rbp)
  addq   $0x1,-0x18(%rbp)
L34:
  cmpl   $0x3,-0x20(%rbp)
  jg     L126
  cmpq   $0x0,-0x18(%rbp)
  je     L126
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  test   %al,%al
  jne    L22
  jmp    L126
L162:
  nop
L126:
  movzbl -0xc(%rbp),%eax
  lea    0x0(,%rax,4),%edx
  movzbl -0xb(%rbp),%eax
  sar    $0x4,%al
  add    %eax,%edx
  mov    -0x30(%rbp),%rax
  mov    %dl,(%rax)
  movzbl -0xb(%rbp),%eax
  shl    $0x4,%eax
  mov    %eax,%edx
  movzbl -0xa(%rbp),%eax
  sar    $0x2,%al
  mov    %eax,%ecx
  mov    -0x30(%rbp),%rax
  add    $0x1,%rax
  add    %ecx,%edx
  mov    %dl,(%rax)
  movzbl -0xa(%rbp),%eax
  shl    $0x6,%eax
  mov    %eax,%edx
  movzbl -0x9(%rbp),%eax
  mov    %eax,%ecx
  mov    -0x30(%rbp),%rax
  add    $0x2,%rax
  add    %ecx,%edx
  mov    %dl,(%rax)
  mov    -0x1c(%rbp),%eax
  mov    -0x8(%rbp),%rdx
  sub    %fs:0x28,%rdx
  je     L188
  call   <__stack_chk_fail@plt>
L188:
  leave
  ret
```

assistant: ```c
int decode_block(unsigned char *in, unsigned char *out) {
  unsigned char *c = in;
  int i = 0, j = 0;
  char temp[4] = {0, 0, 0, 0};
  while (i < 4 && c && *c) {
    if (*c != ' ') {
      if (*c == '+') {
        temp[i] = 62;
      } else if (*c == '/') {
        temp[i] = 63;
      } else if (*c == '=') {
        temp[i] = 0;
      } else if (*c >= '0' && *c <= '9') {
        temp[i] = *c + 4;
      } else if (*c >= 'A' && *c <= 'Z') {
        temp[i] = *c - 65;
      } else if (*c >= 'a' && *c <= 'z') {
        temp[i] = *c - 71;
      } else if (*c == ' ') {
        j++;
      } else {
        break;
      }
      i++;
    }
    j++;
    c++;
  }
  out[0] = (temp[0] << 2) + (temp[1] >> 4);
  out[1] = (temp[1] << 4) + (temp[2] >> 2);
  out[2] = (temp[2] << 6) + (temp[3] >> 0);
  return j;
}
```