user: 这段汇编代码用C语言表示是什么样的:

```asm
<base64_decode>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x40,%rsp
  mov    %rdi,-0x28(%rbp)
  mov    %rsi,-0x30(%rbp)
  mov    %edx,-0x34(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x8(%rbp)
  xor    %eax,%eax
  movl   $0x0,-0x1c(%rbp)
  movl   $0x0,-0x18(%rbp)
  movl   $0x0,-0x14(%rbp)
  mov    -0x34(%rbp),%edx
  mov    -0x30(%rbp),%rax
  mov    $0x0,%esi
  mov    %rax,%rdi
  call   <memset@plt>
  mov    -0x28(%rbp),%rax
  mov    %rax,%rdi
  call   <strlen@plt>
  mov    %eax,-0x20(%rbp)
  jmp    L55
L39:
  mov    -0x14(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x28(%rbp),%rax
  lea    (%rdx,%rax,1),%rcx
  mov    -0x1c(%rbp),%eax
  lea    0x1(%rax),%edx
  mov    %edx,-0x1c(%rbp)
  movzbl (%rcx),%edx
  cltq
  mov    %dl,-0xc(%rbp,%rax,1)
  addl   $0x1,-0x14(%rbp)
  cmpl   $0x4,-0x1c(%rbp)
  jne    L55
  movl   $0x0,-0x1c(%rbp)
  jmp    L113
L10:
  mov    -0x1c(%rbp),%eax
  cltq
  movzbl -0xc(%rbp,%rax,1),%eax
  movzbl %al,%eax
  mov    %eax,%edi
  call   <base64_chars_find@plt>
  mov    -0x1c(%rbp),%edx
  movslq %edx,%rdx
  mov    %al,-0xc(%rbp,%rdx,1)
  addl   $0x1,-0x1c(%rbp)
L113:
  cmpl   $0x3,-0x1c(%rbp)
  jle    L10
  movzbl -0xc(%rbp),%eax
  lea    0x0(,%rax,4),%edx
  movzbl -0xb(%rbp),%eax
  movzbl %al,%eax
  sar    $0x4,%eax
  and    $0x3,%eax
  add    %edx,%eax
  mov    %al,-0xf(%rbp)
  movzbl -0xb(%rbp),%eax
  movzbl %al,%eax
  shl    $0x4,%eax
  mov    %eax,%edx
  movzbl -0xa(%rbp),%eax
  movzbl %al,%eax
  sar    $0x2,%eax
  and    $0xf,%eax
  add    %edx,%eax
  mov    %al,-0xe(%rbp)
  movzbl -0xa(%rbp),%eax
  movzbl %al,%eax
  shl    $0x6,%eax
  mov    %eax,%edx
  movzbl -0x9(%rbp),%eax
  add    %edx,%eax
  mov    %al,-0xd(%rbp)
  movl   $0x0,-0x1c(%rbp)
  jmp    L163
L6:
  mov    -0x30(%rbp),%rax
  mov    %rax,%rdi
  call   <strlen@plt>
  mov    -0x30(%rbp),%rdx
  add    %rax,%rdx
  mov    -0x1c(%rbp),%eax
  cltq
  movzbl -0xf(%rbp,%rax,1),%eax
  mov    %al,(%rdx)
  addl   $0x1,-0x1c(%rbp)
L163:
  cmpl   $0x2,-0x1c(%rbp)
  jg     L25
  mov    -0x30(%rbp),%rax
  mov    %rax,%rdi
  call   <strlen@plt>
  mov    -0x34(%rbp),%edx
  cmp    %rdx,%rax
  jb     L6
L25:
  movl   $0x0,-0x1c(%rbp)
L55:
  mov    -0x20(%rbp),%eax
  lea    -0x1(%rax),%edx
  mov    %edx,-0x20(%rbp)
  test   %eax,%eax
  je     L103
  mov    -0x14(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x3d,%al
  je     L103
  mov    -0x14(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  mov    %eax,%edi
  call   <is_base64@plt>
  test   %rax,%rax
  jne    L39
L103:
  cmpl   $0x0,-0x1c(%rbp)
  je     L71
  mov    -0x1c(%rbp),%eax
  mov    %eax,-0x18(%rbp)
  jmp    L47
L4:
  mov    -0x18(%rbp),%eax
  cltq
  movb   $0x0,-0xc(%rbp,%rax,1)
  addl   $0x1,-0x18(%rbp)
L47:
  cmpl   $0x3,-0x18(%rbp)
  jle    L4
  movl   $0x0,-0x18(%rbp)
  jmp    L149
L78:
  mov    -0x18(%rbp),%eax
  cltq
  movzbl -0xc(%rbp,%rax,1),%eax
  movzbl %al,%eax
  mov    %eax,%edi
  call   <base64_chars_find@plt>
  mov    -0x18(%rbp),%edx
  movslq %edx,%rdx
  mov    %al,-0xc(%rbp,%rdx,1)
  addl   $0x1,-0x18(%rbp)
L149:
  cmpl   $0x3,-0x18(%rbp)
  jle    L78
  movzbl -0xc(%rbp),%eax
  lea    0x0(,%rax,4),%edx
  movzbl -0xb(%rbp),%eax
  movzbl %al,%eax
  sar    $0x4,%eax
  and    $0x3,%eax
  add    %edx,%eax
  mov    %al,-0xf(%rbp)
  movzbl -0xb(%rbp),%eax
  movzbl %al,%eax
  shl    $0x4,%eax
  mov    %eax,%edx
  movzbl -0xa(%rbp),%eax
  movzbl %al,%eax
  sar    $0x2,%eax
  and    $0xf,%eax
  add    %edx,%eax
  mov    %al,-0xe(%rbp)
  movzbl -0xa(%rbp),%eax
  movzbl %al,%eax
  shl    $0x6,%eax
  mov    %eax,%edx
  movzbl -0x9(%rbp),%eax
  add    %edx,%eax
  mov    %al,-0xd(%rbp)
  movl   $0x0,-0x18(%rbp)
  jmp    L151
L174:
  mov    -0x30(%rbp),%rax
  mov    %rax,%rdi
  call   <strlen@plt>
  mov    -0x30(%rbp),%rdx
  add    %rax,%rdx
  mov    -0x18(%rbp),%eax
  cltq
  movzbl -0xf(%rbp,%rax,1),%eax
  mov    %al,(%rdx)
  addl   $0x1,-0x18(%rbp)
L151:
  mov    -0x1c(%rbp),%eax
  sub    $0x1,%eax
  cmp    %eax,-0x18(%rbp)
  jge    L71
  mov    -0x30(%rbp),%rax
  mov    %rax,%rdi
  call   <strlen@plt>
  mov    -0x34(%rbp),%edx
  cmp    %rdx,%rax
  jb     L174
L71:
  mov    -0x30(%rbp),%rax
  mov    %rax,%rdi
  call   <strlen@plt>
  mov    -0x8(%rbp),%rdx
  sub    %fs:0x28,%rdx
  je     L65
  call   <__stack_chk_fail@plt>
L65:
  leave
  ret
```

assistant: ```c
size_t base64_decode(unsigned char const *encoded_string, unsigned char *ret, unsigned int retsize) {
  int in_len, i = 0, j = 0, in_ = 0;
  unsigned char char_array_4[4], char_array_3[3];
  memset(ret, 0, retsize);
  in_len = strlen(encoded_string);
  while (in_len-- && (encoded_string[in_] != '=') && is_base64(encoded_string[in_])) {
    char_array_4[i++] = encoded_string[in_];
    in_++;
    if (i == 4) {
      for (i = 0; i < 4; i++)
        char_array_4[i] = base64_chars_find(char_array_4[i]);
      char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
      char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
      char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];
      for (i = 0; (i < 3) && strlen(ret) < retsize; i++)
        ret[strlen(ret)] = char_array_3[i];
      i = 0;
    }
  }
  if (i) {
    for (j = i; j < 4; j++)
      char_array_4[j] = 0;
    for (j = 0; j < 4; j++)
      char_array_4[j] = base64_chars_find(char_array_4[j]);
    char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
    char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
    char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];
    for (j = 0; (j < i - 1) && strlen(ret) < retsize; j++) {
      ret[strlen(ret)] = char_array_3[j];
    }
  }
  return strlen(ret);
}
```