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

```asm
<dfct>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  mov    %edi,%r12d
  push   %rbp
  sar    %r12d
  mov    %rsi,%rbp
  push   %rbx
  sub    $0x48,%rsp
  mov    %edi,0x34(%rsp)
  test   %r12d,%r12d
  jle    L108
  movslq %edi,%rsi
  movslq %r12d,%r14
  lea    0x8(,%rsi,8),%rcx
  lea    0x0(,%r14,8),%rax
  mov    %rcx,%rdi
  lea    0x0(,%rsi,8),%rdx
  sub    %rax,%rdi
  cmp    %rdi,%rax
  mov    %rbp,%rax
  jg     L117
  cmp    $0x1,%r12d
  je     L117
  lea    -0x10(%rbp,%rcx,1),%rdx
  mov    %r12d,%ecx
  shr    %ecx
  sub    $0x1,%ecx
  shl    $0x4,%rcx
  lea    0x10(%rbp,%rcx,1),%rcx
  nopl   0x0(%rax,%rax,1)
L139:
  movupd (%rdx),%xmm0
  movupd (%rax),%xmm2
  add    $0x10,%rax
  sub    $0x10,%rdx
  movupd -0x10(%rax),%xmm1
  shufpd $0x1,%xmm0,%xmm0
  subpd  %xmm0,%xmm2
  addpd  %xmm0,%xmm1
  movups %xmm2,-0x10(%rax)
  shufpd $0x1,%xmm1,%xmm1
  movups %xmm1,0x10(%rdx)
  cmp    %rcx,%rax
  jne    L139
  mov    %r12d,%ecx
  and    $0xfffffffe,%ecx
  test   $0x1,%r12b
  je     L86
  mov    %ecx,%eax
  lea    0x0(%rbp,%rax,8),%rdx
  mov    0x34(%rsp),%eax
  movsd  (%rdx),%xmm0
  sub    %ecx,%eax
  cltq
  movapd %xmm0,%xmm2
  lea    0x0(%rbp,%rax,8),%rax
  movsd  (%rax),%xmm1
  subsd  %xmm1,%xmm2
  addsd  %xmm1,%xmm0
  movsd  %xmm2,(%rdx)
  movsd  %xmm0,(%rax)
L86:
  lea    0x0(%rbp,%rsi,8),%rax
  movsd  (%rax),%xmm7
  mov    %rax,0x38(%rsp)
  movsd  %xmm7,0x18(%rsp)
L60:
  lea    0x8(%rbp),%r13
  nopl   0x0(%rax,%rax,1)
L123:
  mov    %rbp,%rdx
  mov    $0x1,%esi
  mov    %r12d,%edi
  call   <ddct@plt>
  lea    0x0(,%r14,8),%r15
  mov    %r12d,%edx
  lea    0x0(%rbp,%r15,1),%rbx
  sar    %edx
  cmp    $0x2,%r12d
  jne    L7
  movsd  0x18(%rsp),%xmm7
  movsd  0x0(%rbp),%xmm1
  mov    %edx,%r13d
  movsd  (%rbx),%xmm0
  movsd  %xmm1,(%rbx)
  movapd %xmm7,%xmm1
  subsd  %xmm0,%xmm1
  addsd  %xmm7,%xmm0
  movsd  %xmm1,0x0(%rbp)
  movapd %xmm0,%xmm7
  movsd  %xmm0,0x18(%rsp)
L184:
  movslq %r13d,%rax
  lea    0x0(%rbp,%rax,8),%rdx
  lea    0x0(%r13,%r12,1),%eax
  cltq
  movsd  (%rdx),%xmm0
  lea    0x0(%rbp,%rax,8),%rax
  movsd  (%rax),%xmm1
  movsd  %xmm1,(%rdx)
  movsd  %xmm0,(%rax)
  movsd  0x8(%rbp),%xmm1
  movapd %xmm7,%xmm0
  mov    0x38(%rsp),%rax
  addsd  %xmm1,%xmm0
  subsd  %xmm1,%xmm7
  movhpd 0x0(%rbp),%xmm0
  movups %xmm0,0x0(%rbp)
  movsd  %xmm7,(%rax)
L70:
  mov    0x34(%rsp),%edi
  add    $0x48,%rsp
  mov    %rbp,%rsi
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  jmp    1070 <bitrv1@plt>
  xchg   %ax,%ax
L7:
  mov    %rbp,%rsi
  mov    %r12d,%edi
  mov    %edx,(%rsp)
  call   <bitrv1@plt>
  movsd  0x0(%rbp),%xmm1
  movsd  0x18(%rsp),%xmm6
  movsd  (%rbx),%xmm0
  mov    (%rsp),%edx
  movsd  %xmm1,(%rbx)
  movapd %xmm6,%xmm1
  subsd  %xmm0,%xmm1
  addsd  %xmm6,%xmm0
  movsd  %xmm1,0x0(%rbp)
  movsd  %xmm0,0x18(%rsp)
  cmp    $0x1,%edx
  je     L176
  lea    -0x1(%rdx),%eax
  mov    %r14,%r10
  lea    0x8(%r15),%r9
  lea    0x1(%rax,%r14,1),%rcx
  shl    $0x4,%r10
  mov    %rax,%rdi
  neg    %rax
  lea    (%r15,%rax,8),%r8
  lea    -0x10(%r10),%rax
  mov    %rax,0x8(%rsp)
  lea    (%r8,%r15,1),%rsi
  lea    0x0(%rbp,%r9,1),%rax
  mov    %rsi,(%rsp)
  mov    %edx,%esi
  lea    0x0(,%rcx,8),%r11
  lea    -0x10(%r15),%rcx
  mov    %rax,0x10(%rsp)
  lea    0x18(%rbp,%r15,1),%rax
  shl    $0x3,%rsi
  cmp    %rax,%r13
  mov    %r11,0x20(%rsp)
  lea    0x18(%rbp),%rax
  setae  %r11b
  cmp    %rax,0x10(%rsp)
  mov    %rcx,0x28(%rsp)
  setae  %al
  or     %eax,%r11d
  cmp    %r10,%rcx
  setge  %cl
  cmp    %r15,0x8(%rsp)
  setge  %al
  or     %ecx,%eax
  and    %r11d,%eax
  cmp    $0x2,%edx
  setne  %cl
  and    %ecx,%eax
  cmp    %rbx,%r13
  setae  %cl
  cmp    %r8,%rsi
  setle  %r11b
  or     %r11d,%ecx
  mov    0x20(%rsp),%r11
  and    %eax,%ecx
  lea    (%rbx,%r15,1),%rax
  cmp    %rax,%r13
  setae  %al
  cmp    %rsi,(%rsp)
  setge  %sil
  or     %esi,%eax
  and    %ecx,%eax
  cmp    %r11,%r8
  setge  %cl
  cmp    %r15,%r9
  setge  %sil
  or     %esi,%ecx
  test   %cl,%al
  je     L148
  cmp    %r9,%r10
  setle  %al
  cmp    %r11,(%rsp)
  setge  %cl
  or     %cl,%al
  je     L148
  mov    0x8(%rsp),%r9
  mov    %edi,%r10d
  mov    0x28(%rsp),%rax
  mov    %r13,%rsi
  shr    %r10d
  mov    0x10(%rsp),%rcx
  add    %rbp,%r9
  lea    -0x1(%r10),%r11d
  add    %rbp,%rax
  lea    -0x10(%r9),%r8
  shl    $0x4,%r11
  mov    %r8,%r10
  sub    %r11,%r10
  jmp    L198
  nopl   0x0(%rax)
L175:
  sub    $0x10,%r8
L198:
  movupd (%rax),%xmm2
  movupd (%rsi),%xmm5
  add    $0x10,%rcx
  add    $0x10,%rsi
  movupd (%r9),%xmm0
  movupd -0x10(%rcx),%xmm1
  sub    $0x10,%rax
  movups %xmm5,-0x10(%rcx)
  shufpd $0x1,%xmm0,%xmm0
  movups %xmm2,(%r9)
  movapd %xmm0,%xmm2
  mov    %r8,%r9
  subpd  %xmm1,%xmm2
  addpd  %xmm1,%xmm0
  movups %xmm2,-0x10(%rsi)
  shufpd $0x1,%xmm0,%xmm0
  movups %xmm0,0x10(%rax)
  cmp    %r8,%r10
  jne    L175
  mov    %edi,%eax
  or     $0x1,%eax
  and    $0x1,%edi
  je     L31
  mov    %r12d,%ecx
  sub    %eax,%ecx
  lea    (%r12,%rcx,1),%esi
  movslq %ecx,%rcx
  movslq %esi,%rsi
  lea    0x0(%rbp,%rsi,8),%rdi
  lea    (%r12,%rax,1),%esi
  cltq
  movslq %esi,%rsi
  movsd  (%rdi),%xmm0
  lea    0x0(%rbp,%rsi,8),%r8
  lea    0x0(%rbp,%rax,8),%rsi
  lea    0x0(%rbp,%rcx,8),%rax
  movsd  (%rsi),%xmm3
  movsd  (%r8),%xmm1
  movsd  (%rax),%xmm2
  movsd  %xmm3,(%r8)
  movsd  %xmm2,(%rdi)
  movapd %xmm0,%xmm2
  addsd  %xmm1,%xmm0
  subsd  %xmm1,%xmm2
  movsd  %xmm2,(%rsi)
  movsd  %xmm0,(%rax)
L31:
  add    %edx,%r12d
  movslq %edx,%r14
  movslq %r12d,%r12
  lea    0x0(%rbp,%r14,8),%rcx
  lea    0x0(%rbp,%r12,8),%rax
  movsd  (%rcx),%xmm0
  mov    %edx,%r12d
  movsd  (%rax),%xmm1
  movsd  %xmm1,(%rcx)
  movsd  %xmm0,(%rax)
  jmp    L123
  nop
L148:
  lea    -0x2(%rdx),%ecx
  mov    %rbp,%rax
  lea    0x0(%r13,%rcx,8),%rcx
  nopl   0x0(%rax,%rax,1)
L81:
  movsd  -0x8(%rbx,%r14,8),%xmm0
  movsd  -0x8(%rbx),%xmm2
  movsd  0x8(%rax),%xmm3
  movsd  0x8(%rax,%r14,8),%xmm1
  movsd  %xmm3,0x8(%rax,%r14,8)
  add    $0x8,%rax
  movsd  %xmm2,-0x8(%rbx,%r14,8)
  movapd %xmm0,%xmm2
  addsd  %xmm1,%xmm0
  sub    $0x8,%rbx
  subsd  %xmm1,%xmm2
  movsd  %xmm2,(%rax)
  movsd  %xmm0,(%rbx)
  cmp    %rcx,%rax
  jne    L81
  jmp    L31
L117:
  lea    -0x1(%r12),%ecx
  add    %rbp,%rdx
  lea    0x8(%rbp,%rcx,8),%rcx
  nopl   0x0(%rax)
L171:
  movsd  (%rax),%xmm0
  movsd  (%rdx),%xmm1
  add    $0x8,%rax
  sub    $0x8,%rdx
  movapd %xmm0,%xmm2
  addsd  %xmm1,%xmm0
  subsd  %xmm1,%xmm2
  movsd  %xmm2,-0x8(%rax)
  movsd  %xmm0,0x8(%rdx)
  cmp    %rcx,%rax
  jne    L171
  lea    0x0(%rbp,%rsi,8),%rax
  movsd  (%rax),%xmm7
  mov    %rax,0x38(%rsp)
  movsd  %xmm7,0x18(%rsp)
  cmp    $0x1,%r12d
  jg     L60
L2:
  movsd  0x8(%rbp),%xmm1
  movapd %xmm7,%xmm0
  cmpl   $0x3,0x34(%rsp)
  addsd  %xmm1,%xmm0
  subsd  %xmm1,%xmm7
  movhpd 0x0(%rbp),%xmm0
  movups %xmm0,0x0(%rbp)
  movsd  %xmm7,(%rax)
  je     L70
  add    $0x48,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L108:
  movslq 0x34(%rsp),%rax
  lea    (%rsi,%rax,8),%rax
  movsd  (%rax),%xmm7
  mov    %rax,0x38(%rsp)
  movsd  %xmm7,0x18(%rsp)
  jmp    L2
L176:
  mov    %edx,%r13d
  mov    $0x3,%r12d
  movapd %xmm0,%xmm7
  jmp    L184
```

assistant: ```c
void dfct(int n, double *a) {
  int j, k, m, mh;
  double xr, xi, yr, yi, an;
  m = n >> 1;
  for (j = 0; j < m; j++) {
    k = n - j;
    xr = a[j] + a[k];
    a[j] -= a[k];
    a[k] = xr;
  }
  an = a[n];
  while (m >= 2) {
    ddct(m, 1, a);
    if (m > 2) {
      bitrv1(m, a);
    }
    mh = m >> 1;
    xi = a[m];
    a[m] = a[0];
    a[0] = an - xi;
    an += xi;
    for (j = 1; j < mh; j++) {
      k = m - j;
      xr = a[m + k];
      xi = a[m + j];
      yr = a[j];
      yi = a[k];
      a[m + j] = yr;
      a[m + k] = yi;
      a[j] = xr - xi;
      a[k] = xr + xi;
    }
    xr = a[mh];
    a[mh] = a[m + mh];
    a[m + mh] = xr;
    m = mh;
  }
  xi = a[1];
  a[1] = a[0];
  a[0] = an + xi;
  a[n] = an - xi;
  if (n > 2) {
    bitrv1(n, a);
  }
}
```