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

```asm
<CAST_cfb64_encrypt>:
  endbr64
  push   %r15
  mov    %rdi,%r15
  push   %r14
  mov    %rdx,%r14
  push   %r13
  push   %r12
  mov    %r8,%r12
  push   %rbp
  mov    %rsi,%rbp
  mov    %rcx,%rsi
  push   %rbx
  sub    $0x48,%rsp
  mov    (%r9),%ebx
  mov    %r9,0x18(%rsp)
  mov    %fs:0x28,%rax
  mov    %rax,0x38(%rsp)
  xor    %eax,%eax
  mov    0x80(%rsp),%eax
  test   %eax,%eax
  jne    L42
  mov    %rdi,%r13
  lea    0x20(%rsp),%r9
  test   %rdx,%rdx
  jne    L77
  nopl   0x0(%rax)
L76:
  mov    0x18(%rsp),%rax
  mov    %ebx,(%rax)
  mov    0x38(%rsp),%rax
  sub    %fs:0x28,%rax
  jne    L33
  add    $0x48,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nopw   0x0(%rax,%rax,1)
L104:
  mov    (%r12),%edx
  mov    0x4(%r12),%eax
  mov    %r9,%rdi
  mov    %rsi,0x10(%rsp)
  mov    %r9,0x8(%rsp)
  bswap  %edx
  bswap  %eax
  movd   %edx,%xmm0
  movd   %eax,%xmm1
  punpcklqdq %xmm1,%xmm0
  movaps %xmm0,0x20(%rsp)
  call   <CAST_encrypt@plt>
  mov    0x20(%rsp),%rdi
  mov    0x28(%rsp),%r11
  mov    %rdi,%rdx
  movzbl %r11b,%eax
  mov    %r11,%r10
  mov    %r11,%r8
  shr    $0x18,%rdx
  shl    $0x8,%rax
  mov    %rdi,%rcx
  shr    $0x10,%r10
  mov    %rdx,%r9
  mov    %r11,%rdx
  shr    $0x18,%r8
  movzbl %dh,%esi
  movzbl %r10b,%r10d
  movzbl %r8b,%r8d
  mov    %rdi,%rdx
  or     %rsi,%rax
  shr    $0x10,%rcx
  mov    0x10(%rsp),%rsi
  shl    $0x8,%rax
  movzbl %cl,%ecx
  or     %r10,%rax
  shl    $0x8,%rax
  or     %r8,%rax
  movzbl %dil,%r8d
  movzbl %dh,%edi
  movzbl %r9b,%edx
  shl    $0x8,%rax
  mov    0x8(%rsp),%r9
  or     %r8,%rax
  shl    $0x8,%rax
  or     %rdi,%rax
  shl    $0x8,%rax
  or     %rcx,%rax
  shl    $0x8,%rax
  or     %rdx,%rax
  mov    %rax,(%r12)
L67:
  movslq %ebx,%rdx
  movzbl 0x0(%r13),%eax
  add    $0x1,%rbp
  add    $0x1,%r13
  add    %r12,%rdx
  add    $0x1,%ebx
  movzbl (%rdx),%ecx
  mov    %al,(%rdx)
  and    $0x7,%ebx
  xor    %ecx,%eax
  mov    %al,-0x1(%rbp)
  mov    %r15,%rax
  sub    %r13,%rax
  add    %r14,%rax
  je     L76
L77:
  test   %ebx,%ebx
  jne    L67
  jmp    L104
  cs nopw 0x0(%rax,%rax,1)
L42:
  test   %rdx,%rdx
  je     L76
  lea    0x20(%rsp),%rax
  mov    %rbp,%r12
  mov    %rdi,%r13
  mov    %rdx,%rbp
  mov    %rax,0x10(%rsp)
  mov    %r8,%r14
  jmp    L8
  nopl   0x0(%rax)
L85:
  movslq %ebx,%rax
  movzbl 0x0(%r13),%ecx
  add    $0x1,%r12
  add    $0x1,%r13
  add    %r14,%rax
  add    $0x1,%ebx
  xor    (%rax),%cl
  and    $0x7,%ebx
  mov    %cl,-0x1(%r12)
  mov    %cl,(%rax)
  mov    %r15,%rax
  sub    %r13,%rax
  add    %rbp,%rax
  je     L76
L8:
  test   %ebx,%ebx
  jne    L85
  mov    (%r14),%ecx
  mov    0x4(%r14),%eax
  mov    %rsi,0x8(%rsp)
  mov    0x10(%rsp),%rdi
  bswap  %ecx
  bswap  %eax
  movd   %ecx,%xmm0
  movd   %eax,%xmm1
  punpcklqdq %xmm1,%xmm0
  movaps %xmm0,0x20(%rsp)
  call   <CAST_encrypt@plt>
  mov    0x28(%rsp),%r11
  mov    0x20(%rsp),%rdx
  mov    %r11,%rax
  movzbl %r11b,%esi
  mov    %r11,%r9
  mov    %r11,%r10
  movzbl %ah,%eax
  shr    $0x10,%r10
  mov    %rdx,%rdi
  mov    %rdx,%rcx
  shr    $0x18,%r9
  mov    %rax,%r11
  mov    %rsi,%rax
  movzbl %r10b,%r10d
  shl    $0x8,%rax
  movzbl %r9b,%r9d
  movzbl %dh,%esi
  shr    $0x10,%rdi
  or     %r11,%rax
  movzbl %dil,%edi
  shr    $0x18,%rcx
  shl    $0x8,%rax
  movzbl %cl,%ecx
  or     %r10,%rax
  shl    $0x8,%rax
  or     %r9,%rax
  movzbl %dl,%r9d
  shl    $0x8,%rax
  or     %r9,%rax
  shl    $0x8,%rax
  or     %rsi,%rax
  mov    0x8(%rsp),%rsi
  shl    $0x8,%rax
  or     %rdi,%rax
  shl    $0x8,%rax
  or     %rcx,%rax
  mov    %rax,(%r14)
  jmp    L85
L33:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
void CAST_cfb64_encrypt(const unsigned char *in, unsigned char *out, long length, const CAST_KEY *schedule, unsigned char *ivec, int *num, int enc) {
  register CAST_LONG v0, v1, t;
  register int n = *num;
  register long l = length;
  CAST_LONG ti[2];
  unsigned char *iv, c, cc;
  iv = ivec;
  if (enc) {
    while (l--) {
      if (n == 0) {
        (v0 = ((unsigned long)(*((iv)++))) << 24L, v0 |= ((unsigned long)(*((iv)++))) << 16L, v0 |= ((unsigned long)(*((iv)++))) << 8L, v0 |= ((unsigned long)(*((iv)++))));
        ti[0] = v0;
        (v1 = ((unsigned long)(*((iv)++))) << 24L, v1 |= ((unsigned long)(*((iv)++))) << 16L, v1 |= ((unsigned long)(*((iv)++))) << 8L, v1 |= ((unsigned long)(*((iv)++))));
        ti[1] = v1;
        CAST_encrypt((CAST_LONG *)ti, schedule);
        iv = ivec;
        t = ti[0];
        (*((iv)++) = (unsigned char)(((t) >> 24L) & 0xff), *((iv)++) = (unsigned char)(((t) >> 16L) & 0xff), *((iv)++) = (unsigned char)(((t) >> 8L) & 0xff), *((iv)++) = (unsigned char)(((t)) & 0xff));
        t = ti[1];
        (*((iv)++) = (unsigned char)(((t) >> 24L) & 0xff), *((iv)++) = (unsigned char)(((t) >> 16L) & 0xff), *((iv)++) = (unsigned char)(((t) >> 8L) & 0xff), *((iv)++) = (unsigned char)(((t)) & 0xff));
        iv = ivec;
      }
      c = *(in++) ^ iv[n];
      *(out++) = c;
      iv[n] = c;
      n = (n + 1) & 0x07;
    }
  } else {
    while (l--) {
      if (n == 0) {
        (v0 = ((unsigned long)(*((iv)++))) << 24L, v0 |= ((unsigned long)(*((iv)++))) << 16L, v0 |= ((unsigned long)(*((iv)++))) << 8L, v0 |= ((unsigned long)(*((iv)++))));
        ti[0] = v0;
        (v1 = ((unsigned long)(*((iv)++))) << 24L, v1 |= ((unsigned long)(*((iv)++))) << 16L, v1 |= ((unsigned long)(*((iv)++))) << 8L, v1 |= ((unsigned long)(*((iv)++))));
        ti[1] = v1;
        CAST_encrypt((CAST_LONG *)ti, schedule);
        iv = ivec;
        t = ti[0];
        (*((iv)++) = (unsigned char)(((t) >> 24L) & 0xff), *((iv)++) = (unsigned char)(((t) >> 16L) & 0xff), *((iv)++) = (unsigned char)(((t) >> 8L) & 0xff), *((iv)++) = (unsigned char)(((t)) & 0xff));
        t = ti[1];
        (*((iv)++) = (unsigned char)(((t) >> 24L) & 0xff), *((iv)++) = (unsigned char)(((t) >> 16L) & 0xff), *((iv)++) = (unsigned char)(((t) >> 8L) & 0xff), *((iv)++) = (unsigned char)(((t)) & 0xff));
        iv = ivec;
      }
      cc = *(in++);
      c = iv[n];
      iv[n] = cc;
      *(out++) = c ^ cc;
      n = (n + 1) & 0x07;
    }
  }
  v0 = v1 = ti[0] = ti[1] = t = c = cc = 0;
  *num = n;
}
```