user: Translate the below assembly code into C programming language:

```asm
<decode_quantum>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  mov    %rdi,-0x18(%rbp)
  mov    %rsi,-0x20(%rbp)
  movl   $0x0,-0x8(%rbp)
  movl   $0x0,-0x4(%rbp)
  jmp    L93
L89:
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x40,%al
  jle    L143
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x5a,%al
  jg     L143
  mov    -0x8(%rbp),%eax
  shl    $0x6,%eax
  mov    %eax,%ecx
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  add    %ecx,%eax
  sub    $0x41,%eax
  mov    %eax,-0x8(%rbp)
  jmp    L9
L143:
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x60,%al
  jle    L71
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x7a,%al
  jg     L71
  mov    -0x8(%rbp),%eax
  shl    $0x6,%eax
  mov    %eax,%ecx
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  add    %ecx,%eax
  sub    $0x47,%eax
  mov    %eax,-0x8(%rbp)
  jmp    L9
L71:
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x2f,%al
  jle    L7
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x39,%al
  jg     L7
  mov    -0x8(%rbp),%eax
  shl    $0x6,%eax
  mov    %eax,%ecx
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  add    %ecx,%eax
  add    $0x4,%eax
  mov    %eax,-0x8(%rbp)
  jmp    L9
L7:
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x2b,%al
  jne    L30
  mov    -0x8(%rbp),%eax
  shl    $0x6,%eax
  add    $0x3e,%eax
  mov    %eax,-0x8(%rbp)
  jmp    L9
L30:
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x2f,%al
  jne    L38
  mov    -0x8(%rbp),%eax
  shl    $0x6,%eax
  add    $0x3f,%eax
  mov    %eax,-0x8(%rbp)
  jmp    L9
L38:
  mov    -0x4(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x20(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x3d,%al
  jne    L9
  shll   $0x6,-0x8(%rbp)
L9:
  addl   $0x1,-0x4(%rbp)
L93:
  cmpl   $0x3,-0x4(%rbp)
  jle    L89
  mov    -0x18(%rbp),%rax
  add    $0x2,%rax
  mov    -0x8(%rbp),%edx
  mov    %dl,(%rax)
  shrl   $0x8,-0x8(%rbp)
  mov    -0x18(%rbp),%rax
  add    $0x1,%rax
  mov    -0x8(%rbp),%edx
  mov    %dl,(%rax)
  shrl   $0x8,-0x8(%rbp)
  mov    -0x8(%rbp),%eax
  mov    %eax,%edx
  mov    -0x18(%rbp),%rax
  mov    %dl,(%rax)
  nop
  pop    %rbp
  ret
```

assistant: ```c
void decode_quantum(unsigned char *dest, const char *src) {
  unsigned int x = 0;
  int i;
  for (i = 0; i < 4; i++) {
    if (src[i] >= 'A' && src[i] <= 'Z')
      x = (x << 6) + (unsigned int)(src[i] - 'A' + 0);
    else if (src[i] >= 'a' && src[i] <= 'z')
      x = (x << 6) + (unsigned int)(src[i] - 'a' + 26);
    else if (src[i] >= '0' && src[i] <= '9')
      x = (x << 6) + (unsigned int)(src[i] - '0' + 52);
    else if (src[i] == '+')
      x = (x << 6) + 62;
    else if (src[i] == '/')
      x = (x << 6) + 63;
    else if (src[i] == '=')
      x = (x << 6);
  }
  dest[2] = (unsigned char)(x & 255);
  x >>= 8;
  dest[1] = (unsigned char)(x & 255);
  x >>= 8;
  dest[0] = (unsigned char)(x & 255);
}
```