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

```asm
<divbwt>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  mov    %rdx,%r12
  mov    %ecx,%edx
  push   %rbp
  push   %rbx
  sub    $0x18,%rsp
  test   %rsi,%rsi
  sete   %al
  shr    $0x1f,%edx
  or     %dl,%al
  jne    L115
  mov    %rdi,%r14
  test   %rdi,%rdi
  je     L115
  mov    %rsi,%rbp
  mov    %ecx,%ebx
  cmp    $0x1,%ecx
  jle    L3
  test   %r12,%r12
  je     L33
  mov    $0x400,%edi
  call   <malloc@plt>
  mov    $0x40000,%edi
  mov    %rax,%r13
  call   <malloc@plt>
  mov    %rax,%r15
  test   %r13,%r13
  je     L157
  mov    %r13,%r10
  test   %rax,%rax
  jne    L150
  xor    %edi,%edi
  mov    $0xfffffffe,%ebx
  call   <free@plt>
  mov    %r13,%rdi
  call   <free@plt>
  jmp    L203
  nopl   0x0(%rax,%rax,1)
L157:
  mov    %r15,%rdi
  mov    $0xfffffffe,%ebx
  call   <free@plt>
  xor    %edi,%edi
  call   <free@plt>
L203:
  add    $0x18,%rsp
  mov    %ebx,%eax
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nopl   (%rax)
L3:
  mov    $0x0,%ebx
  jne    L203
  movzbl (%rdi),%eax
  mov    $0x1,%ebx
  mov    %al,(%rsi)
  jmp    L203
  nopl   0x0(%rax,%rax,1)
L33:
  lea    0x4(,%rcx,4),%edi
  call   <malloc@plt>
  mov    $0x400,%edi
  mov    %rax,%r13
  call   <malloc@plt>
  mov    $0x40000,%edi
  mov    %rax,(%rsp)
  mov    %rax,0x8(%rsp)
  call   <malloc@plt>
  test   %r13,%r13
  mov    (%rsp),%r8
  mov    %rax,%rdi
  mov    %rax,%r15
  je     L17
  test   %r8,%r8
  mov    0x8(%rsp),%r10
  je     L17
  test   %rax,%rax
  jne    L9
  mov    %r8,(%rsp)
  xor    %edi,%edi
  jmp    L181
  nopl   (%rax)
L150:
  mov    %r12,%r13
L9:
  mov    %r10,%rdx
  mov    %ebx,%r8d
  mov    %r15,%rcx
  mov    %r13,%rsi
  mov    %r14,%rdi
  mov    %r10,(%rsp)
  call   <sort_typeBstar@plt>
  mov    (%rsp),%rdx
  mov    %ebx,%r8d
  mov    %r15,%rcx
  mov    %eax,%r9d
  mov    %r13,%rsi
  mov    %r14,%rdi
  call   <construct_BWT@plt>
  movslq %ebx,%rdx
  mov    (%rsp),%r10
  movzbl -0x1(%r14,%rdx,1),%edx
  test   %eax,%eax
  mov    %dl,0x0(%rbp)
  jle    L49
  mov    %eax,%esi
  xor    %edx,%edx
  nop
L123:
  mov    0x0(%r13,%rdx,4),%ecx
  mov    %cl,0x1(%rbp,%rdx,1)
  add    $0x1,%rdx
  cmp    %rdx,%rsi
  jne    L123
  add    $0x1,%eax
  movslq %eax,%rdx
  cmp    %eax,%ebx
  jle    L212
  nopl   0x0(%rax)
L199:
  mov    0x0(%r13,%rdx,4),%ecx
  mov    %cl,0x0(%rbp,%rdx,1)
  add    $0x1,%rdx
  cmp    %edx,%ebx
  jg     L199
L212:
  mov    %r15,%rdi
  mov    %r10,(%rsp)
  mov    %eax,%ebx
  call   <free@plt>
  mov    (%rsp),%rdi
  call   <free@plt>
  test   %r12,%r12
  jne    L203
  mov    %r13,%rdi
  call   <free@plt>
  jmp    L203
  xchg   %ax,%ax
L17:
  mov    %r8,(%rsp)
L181:
  call   <free@plt>
  mov    (%rsp),%rdi
  mov    $0xfffffffe,%ebx
  call   <free@plt>
  mov    %r13,%rdi
  call   <free@plt>
  jmp    L203
  nopl   0x0(%rax)
L115:
  mov    $0xffffffff,%ebx
  jmp    L203
  nopw   0x0(%rax,%rax,1)
L49:
  mov    $0x1,%edx
  add    $0x1,%eax
  jmp    L199
```

assistant: ```c
int divbwt(const unsigned char *T, unsigned char *U, int *A, int n) {
  int *B;
  int *bucket_A, *bucket_B;
  int m, pidx, i;
  if ((T == NULL) || (U == NULL) || (n < 0)) {
    return -1;
  } else if (n <= 1) {
    if (n == 1) {
      U[0] = T[0];
    }
    return n;
  }
  if ((B = A) == NULL) {
    B = (int *)malloc((size_t)(n + 1) * sizeof(int));
  }
  bucket_A = (int *)malloc(((256)) * sizeof(int));
  bucket_B = (int *)malloc(((256) * (256)) * sizeof(int));
  if ((B != NULL) && (bucket_A != NULL) && (bucket_B != NULL)) {
    m = sort_typeBstar(T, B, bucket_A, bucket_B, n);
    pidx = construct_BWT(T, B, bucket_A, bucket_B, n, m);
    U[0] = T[n - 1];
    for (i = 0; i < pidx; ++i) {
      U[i + 1] = (unsigned char)B[i];
    }
    for (i += 1; i < n; ++i) {
      U[i] = (unsigned char)B[i];
    }
    pidx += 1;
  } else {
    pidx = -2;
  }
  free(bucket_B);
  free(bucket_A);
  if (A == NULL) {
    free(B);
  }
  return pidx;
}
```