user: 提供的汇编代码用C语言表示会是什么样子:

```asm
<uh_b64decode>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  mov    %rdi,-0x18(%rbp)
  mov    %esi,-0x1c(%rbp)
  mov    %rdx,-0x28(%rbp)
  mov    %ecx,-0x20(%rbp)
  movl   $0x0,-0x10(%rbp)
  movl   $0x0,-0xc(%rbp)
  movl   $0x0,-0x8(%rbp)
  movl   $0x0,-0x4(%rbp)
  movl   $0x0,-0x10(%rbp)
  jmp    L16
L27:
  mov    -0x10(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  mov    %eax,-0x8(%rbp)
  cmpl   $0x2f,-0x8(%rbp)
  jbe    L3
  cmpl   $0x39,-0x8(%rbp)
  ja     L3
  addl   $0x4,-0x8(%rbp)
  jmp    L197
L3:
  cmpl   $0x40,-0x8(%rbp)
  jbe    L124
  cmpl   $0x5a,-0x8(%rbp)
  ja     L124
  subl   $0x41,-0x8(%rbp)
  jmp    L197
L124:
  cmpl   $0x60,-0x8(%rbp)
  jbe    L73
  cmpl   $0x7a,-0x8(%rbp)
  ja     L73
  subl   $0x47,-0x8(%rbp)
  jmp    L197
L73:
  cmpl   $0x2b,-0x8(%rbp)
  jne    L127
  movl   $0x3e,-0x8(%rbp)
  jmp    L197
L127:
  cmpl   $0x2f,-0x8(%rbp)
  jne    L129
  movl   $0x3f,-0x8(%rbp)
  jmp    L197
L129:
  cmpl   $0x3d,-0x8(%rbp)
  jne    L116
  movl   $0x0,-0x8(%rbp)
L197:
  mov    -0x4(%rbp),%eax
  shl    $0x6,%eax
  or     -0x8(%rbp),%eax
  mov    %eax,-0x4(%rbp)
  mov    -0x10(%rbp),%eax
  cltd
  shr    $0x1e,%edx
  add    %edx,%eax
  and    $0x3,%eax
  sub    %edx,%eax
  cmp    $0x3,%eax
  jne    L144
  mov    -0xc(%rbp),%eax
  add    $0x3,%eax
  cmp    %eax,-0x1c(%rbp)
  jle    L146
  mov    -0x4(%rbp),%eax
  shr    $0x10,%eax
  mov    %eax,%ecx
  mov    -0xc(%rbp),%eax
  lea    0x1(%rax),%edx
  mov    %edx,-0xc(%rbp)
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    %ecx,%edx
  mov    %dl,(%rax)
  mov    -0x4(%rbp),%eax
  shr    $0x8,%eax
  mov    %eax,%ecx
  mov    -0xc(%rbp),%eax
  lea    0x1(%rax),%edx
  mov    %edx,-0xc(%rbp)
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    %ecx,%edx
  mov    %dl,(%rax)
  mov    -0xc(%rbp),%eax
  lea    0x1(%rax),%edx
  mov    %edx,-0xc(%rbp)
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    -0x4(%rbp),%edx
  mov    %dl,(%rax)
  jmp    L144
L116:
  nop
L144:
  addl   $0x1,-0x10(%rbp)
L16:
  mov    -0x10(%rbp),%eax
  cmp    -0x20(%rbp),%eax
  jg     L42
  mov    -0x10(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  test   %al,%al
  jne    L27
  jmp    L42
L146:
  nop
L42:
  mov    -0xc(%rbp),%eax
  lea    0x1(%rax),%edx
  mov    %edx,-0xc(%rbp)
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movb   $0x0,(%rax)
  mov    -0xc(%rbp),%eax
  pop    %rbp
  ret
```

assistant: ```c
int uh_b64decode(char *buf, int blen, const unsigned char *src, int slen) {
  int i = 0;
  int len = 0;
  unsigned int cin = 0;
  unsigned int cout = 0;
  for (i = 0; (i <= slen) && (src[i] != 0); i++) {
    cin = src[i];
    if ((cin >= '0') && (cin <= '9'))
      cin = cin - '0' + 52;
    else if ((cin >= 'A') && (cin <= 'Z'))
      cin = cin - 'A';
    else if ((cin >= 'a') && (cin <= 'z'))
      cin = cin - 'a' + 26;
    else if (cin == '+')
      cin = 62;
    else if (cin == '/')
      cin = 63;
    else if (cin == '=')
      cin = 0;
    else
      continue;
    cout = (cout << 6) | cin;
    if ((i % 4) == 3) {
      if ((len + 3) < blen) {
        buf[len++] = (char)(cout >> 16);
        buf[len++] = (char)(cout >> 8);
        buf[len++] = (char)(cout);
      } else {
        break;
      }
    }
  }
  buf[len++] = 0;
  return len;
}
```