user: 请显示与下面列出的汇编代码相匹配的C语言实现：

```asm
<base64_decode>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x90,%rsp
  mov    %rdi,-0x88(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x8(%rbp)
  xor    %eax,%eax
  mov    -0x88(%rbp),%rax
  mov    %rax,%rdi
  call   <strlen@plt>
  sub    $0x1,%eax
  movslq %eax,%rdx
  imul   $0x55555556,%rdx,%rdx
  shr    $0x20,%rdx
  sar    $0x1f,%eax
  mov    %eax,%ecx
  mov    %edx,%eax
  sub    %ecx,%eax
  add    $0x1,%eax
  shl    $0x2,%eax
  add    $0x32,%eax
  mov    %eax,%edi
  call   <malloc@plt>
  mov    %rax,-0x68(%rbp)
  movabs $0x4847464544434241,%rax
  movabs $0x504f4e4d4c4b4a49,%rdx
  mov    %rax,-0x50(%rbp)
  mov    %rdx,-0x48(%rbp)
  movabs $0x5857565554535251,%rax
  movabs $0x6665646362615a59,%rdx
  mov    %rax,-0x40(%rbp)
  mov    %rdx,-0x38(%rbp)
  movabs $0x6e6d6c6b6a696867,%rax
  movabs $0x767574737271706f,%rdx
  mov    %rax,-0x30(%rbp)
  mov    %rdx,-0x28(%rbp)
  movabs $0x333231307a797877,%rax
  movabs $0x2f2b393837363534,%rdx
  mov    %rax,-0x20(%rbp)
  mov    %rdx,-0x18(%rbp)
  movb   $0x0,-0x10(%rbp)
  mov    -0x68(%rbp),%rax
  movb   $0x0,(%rax)
  movl   $0x0,-0x74(%rbp)
  movl   $0x0,-0x70(%rbp)
  jmp    L1
L48:
  mov    -0x70(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x88(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  mov    %eax,-0x6c(%rbp)
  cmpl   $0x3d,-0x6c(%rbp)
  jne    L57
  mov    -0x68(%rbp),%rdx
  lea    -0x54(%rbp),%rax
  mov    %rdx,%rsi
  mov    %rax,%rdi
  call   <decodeblock@plt>
  jmp    L59
L57:
  mov    -0x6c(%rbp),%edx
  lea    -0x50(%rbp),%rax
  mov    %edx,%esi
  mov    %rax,%rdi
  call   <strchr@plt>
  mov    %rax,-0x60(%rbp)
  cmpq   $0x0,-0x60(%rbp)
  je     L44
  lea    -0x50(%rbp),%rdx
  mov    -0x60(%rbp),%rax
  sub    %rdx,%rax
  mov    %eax,%edx
  mov    -0x74(%rbp),%eax
  cltq
  mov    %dl,-0x54(%rbp,%rax,1)
  mov    -0x74(%rbp),%eax
  add    $0x1,%eax
  cltd
  shr    $0x1e,%edx
  add    %edx,%eax
  and    $0x3,%eax
  sub    %edx,%eax
  mov    %eax,-0x74(%rbp)
  cmpl   $0x0,-0x74(%rbp)
  jne    L44
  mov    -0x68(%rbp),%rdx
  lea    -0x54(%rbp),%rax
  mov    %rdx,%rsi
  mov    %rax,%rdi
  call   <decodeblock@plt>
  movb   $0x0,-0x51(%rbp)
  movzbl -0x51(%rbp),%eax
  mov    %al,-0x52(%rbp)
  movzbl -0x52(%rbp),%eax
  mov    %al,-0x53(%rbp)
  movzbl -0x53(%rbp),%eax
  mov    %al,-0x54(%rbp)
L44:
  addl   $0x1,-0x70(%rbp)
L1:
  mov    -0x70(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x88(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  test   %al,%al
  jne    L48
L59:
  mov    -0x68(%rbp),%rax
  mov    %rax,%rdi
  call   <strlen@plt>
  lea    0x1(%rax),%edx
  mov    -0x68(%rbp),%rax
  mov    %edx,%esi
  mov    %rax,%rdi
  call   <realloc@plt>
  mov    %rax,-0x68(%rbp)
  mov    -0x68(%rbp),%rax
  mov    -0x8(%rbp),%rdx
  sub    %fs:0x28,%rdx
  je     L32
  call   <__stack_chk_fail@plt>
L32:
  leave
  ret
```

assistant: ```c
char *base64_decode(char *b64src) {
  char *clrdst = (char *)malloc(((strlen(b64src) - 1) / 3) * 4 + 4 + 50);
  char b64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
  int c, phase, i;
  unsigned char in[4];
  char *p;
  clrdst[0] = '\0';
  phase = 0;
  i = 0;
  while (b64src[i]) {
    c = (int)b64src[i];
    if (c == '=') {
      decodeblock(in, clrdst);
      break;
    }
    p = strchr(b64, c);
    if (p) {
      in[phase] = p - b64;
      phase = (phase + 1) % 4;
      if (phase == 0) {
        decodeblock(in, clrdst);
        in[0] = in[1] = in[2] = in[3] = 0;
      }
    }
    i++;
  }
  clrdst = (char *)realloc(clrdst, strlen(clrdst) + 1);
  return clrdst;
}
```