user: Demonstrate the C code that generates the assembly output below:

```asm
<base64_decode>:
  endbr64
  push   %r13
  push   %r12
  mov    %rdi,%r12
  push   %rbp
  mov    %rsi,%rbp
  push   %rbx
  mov    %rdx,%rbx
  sub    $0x18,%rsp
  mov    %fs:0x28,%rax
  mov    %rax,0x8(%rsp)
  xor    %eax,%eax
  movl   $0x0,0x4(%rsp)
  call   <strlen@plt>
  test   %eax,%eax
  jle    L50
  mov    %rbx,%rdi
  mov    %eax,%r13d
  call   <strlen@plt>
  test   %eax,%eax
  jle    L238
  mov    %r12,%rdi
  lea    0x4(%rsp),%rdx
  mov    %r13d,%esi
  call   <base64decode@plt>
  mov    %rax,%rdi
  mov    0x4(%rsp),%eax
  test   %eax,%eax
  jle    L8
  cmp    $0x40,%eax
  jg     L168
  lea    0x1(%rbx),%r8
  mov    %rbp,%rcx
  lea    -0x1(%rax),%edx
  mov    %eax,%esi
  sub    %r8,%rcx
  cmp    $0xe,%rcx
  seta   %r8b
  cmp    $0x6,%edx
  seta   %cl
  test   %cl,%r8b
  je     L90
  lea    0x1(%rdi),%r8
  mov    %rbp,%rcx
  sub    %r8,%rcx
  cmp    $0xe,%rcx
  jbe    L90
  cmp    $0xe,%edx
  jbe    L256
  movdqu (%rdi),%xmm0
  movdqu (%rbx),%xmm2
  mov    %eax,%edx
  shr    $0x4,%edx
  pxor   %xmm2,%xmm0
  movups %xmm0,0x0(%rbp)
  cmp    $0x1,%edx
  je     L219
  movdqu 0x10(%rdi),%xmm0
  movdqu 0x10(%rbx),%xmm3
  pxor   %xmm3,%xmm0
  movups %xmm0,0x10(%rbp)
  cmp    $0x2,%edx
  je     L219
  movdqu 0x20(%rdi),%xmm0
  movdqu 0x20(%rbx),%xmm4
  pxor   %xmm4,%xmm0
  movups %xmm0,0x20(%rbp)
  cmp    $0x4,%edx
  jne    L219
  movdqu 0x30(%rbx),%xmm0
  movdqu 0x30(%rdi),%xmm5
  pxor   %xmm5,%xmm0
  movups %xmm0,0x30(%rbp)
L223:
  call   <free@plt>
  xor    %eax,%eax
L75:
  mov    0x8(%rsp),%rdx
  sub    %fs:0x28,%rdx
  jne    L250
  add    $0x18,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  ret
  nopw   0x0(%rax,%rax,1)
L219:
  mov    %eax,%edx
  and    $0xfffffff0,%edx
  mov    %edx,%ecx
  cmp    %edx,%eax
  je     L223
  mov    %eax,%esi
  sub    %edx,%esi
  lea    -0x1(%rsi),%r8d
  cmp    $0x6,%r8d
  jbe    L17
L53:
  movq   (%rdi,%rdx,1),%xmm0
  movq   (%rbx,%rdx,1),%xmm1
  pxor   %xmm1,%xmm0
  movq   %xmm0,0x0(%rbp,%rdx,1)
  mov    %esi,%edx
  and    $0xfffffff8,%edx
  add    %edx,%ecx
  cmp    %esi,%edx
  je     L223
L17:
  movslq %ecx,%rdx
  movzbl (%rdi,%rdx,1),%esi
  xor    (%rbx,%rdx,1),%sil
  mov    %sil,0x0(%rbp,%rdx,1)
  lea    0x1(%rcx),%edx
  cmp    %edx,%eax
  jle    L223
  movslq %edx,%rdx
  movzbl (%rdi,%rdx,1),%esi
  xor    (%rbx,%rdx,1),%sil
  mov    %sil,0x0(%rbp,%rdx,1)
  lea    0x2(%rcx),%edx
  cmp    %edx,%eax
  jle    L223
  movslq %edx,%rdx
  movzbl (%rdi,%rdx,1),%esi
  xor    (%rbx,%rdx,1),%sil
  mov    %sil,0x0(%rbp,%rdx,1)
  lea    0x3(%rcx),%edx
  cmp    %edx,%eax
  jle    L223
  movslq %edx,%rdx
  movzbl (%rdi,%rdx,1),%esi
  xor    (%rbx,%rdx,1),%sil
  mov    %sil,0x0(%rbp,%rdx,1)
  lea    0x4(%rcx),%edx
  cmp    %edx,%eax
  jle    L223
  movslq %edx,%rdx
  movzbl (%rdi,%rdx,1),%esi
  xor    (%rbx,%rdx,1),%sil
  mov    %sil,0x0(%rbp,%rdx,1)
  lea    0x5(%rcx),%edx
  cmp    %edx,%eax
  jle    L223
  movslq %edx,%rdx
  add    $0x6,%ecx
  movzbl (%rdi,%rdx,1),%esi
  xor    (%rbx,%rdx,1),%sil
  mov    %sil,0x0(%rbp,%rdx,1)
  cmp    %ecx,%eax
  jle    L223
  movslq %ecx,%rcx
  movzbl (%rdi,%rcx,1),%eax
  xor    (%rbx,%rcx,1),%al
  mov    %al,0x0(%rbp,%rcx,1)
  jmp    L223
  nopl   0x0(%rax)
L90:
  xor    %edx,%edx
  nopw   0x0(%rax,%rax,1)
L14:
  movzbl (%rdi,%rdx,1),%ecx
  xor    (%rbx,%rdx,1),%cl
  mov    %cl,0x0(%rbp,%rdx,1)
  add    $0x1,%rdx
  cmp    %rax,%rdx
  jne    L14
  jmp    L223
L256:
  xor    %edx,%edx
  xor    %ecx,%ecx
  jmp    L53
L238:
  mov    $0xfffffffe,%eax
  jmp    L75
L50:
  mov    $0xffffffff,%eax
  jmp    L75
L168:
  mov    $0xfffffffc,%eax
  jmp    L75
L8:
  mov    $0xfffffffd,%eax
  jmp    L75
L250:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
int base64_decode(char *source, char *dest, char *scramble_string) {
  int i = 0, lenSource = 0, lenScramble = 0, len = 0;
  lenSource = strlen(source);
  if (lenSource < 1)
    return -1;
  lenScramble = strlen(scramble_string);
  if (lenScramble < 1)
    return -2;
  char *base64_decode;
  base64_decode = base64decode(source, lenSource, &len);
  if (len < 1)
    return -3;
  if (len > 64)
    return -4;
  for (i = 0; i < len; i++)
    dest[i] = base64_decode[i] ^ scramble_string[i];
  free(base64_decode);
  return 0;
}
```