user: What is the c source code of the assembly code below?

```asm
<dfft>:
  endbr64
  push   %r15
  push   %r14
  mov    %rcx,%r14
  push   %r13
  mov    %edi,%r13d
  push   %r12
  push   %rbp
  mov    %rdx,%rbp
  mov    %rcx,%rdx
  push   %rbx
  mov    %esi,%ebx
  mov    %ebx,%r15d
  shr    $0x1f,%r15d
  sub    $0x18,%rsp
  add    %ebx,%r15d
  mov    %esi,0xc(%rsp)
  mov    %rbp,%rsi
  sar    %r15d
  call   <cft1st@plt>
  cmp    $0x7,%ebx
  jle    L44
  mov    %r15d,%r12d
  mov    $0x8,%ebx
  mov    $0x4,%r15d
L22:
  mov    %ebx,%esi
  mov    %r14,%rcx
  mov    %rbp,%rdx
  mov    %r13d,%edi
  call   <cftmd1@plt>
  add    $0x2,%r15d
  shl    $0x2,%ebx
  cmp    %r12d,%r15d
  jle    L22
L13:
  mov    0xc(%rsp),%eax
  cmp    %eax,%r15d
  jge    L45
  mov    %eax,%r12d
  sub    $0x1,%r12d
  sub    %r15d,%r12d
  xor    %r15d,%r15d
  shr    %r12d
  nopl   (%rax)
L56:
  mov    %ebx,%esi
  mov    %r14,%rcx
  mov    %rbp,%rdx
  mov    %r13d,%edi
  call   <cftmd2@plt>
  mov    %r15d,%eax
  shl    $0x2,%ebx
  add    $0x1,%r15d
  cmp    %eax,%r12d
  jne    L56
L45:
  movslq %ebx,%r14
  lea    0x0(,%rbx,4),%eax
  shl    $0x3,%r14
  lea    0x0(%rbp,%r14,1),%r12
  cmp    %r13d,%eax
  je     L24
  sub    $0x1,%ebx
  lea    0x8(%rbp),%rax
  lea    0x8(%r12),%rdx
  shr    %ebx
  shl    $0x4,%rbx
  lea    0x18(%rbp,%rbx,1),%rcx
  nopw   0x0(%rax,%rax,1)
L25:
  movsd  (%rax),%xmm0
  movsd  (%rdx),%xmm2
  add    $0x10,%rax
  add    $0x10,%rdx
  movsd  -0x18(%rax),%xmm1
  movsd  -0x18(%rdx),%xmm3
  movapd %xmm1,%xmm4
  subsd  %xmm3,%xmm1
  addsd  %xmm3,%xmm4
  movsd  %xmm4,-0x18(%rax)
  movapd %xmm0,%xmm4
  subsd  %xmm2,%xmm0
  addsd  %xmm2,%xmm4
  movsd  %xmm4,-0x10(%rax)
  movsd  %xmm1,-0x18(%rdx)
  movsd  %xmm0,-0x10(%rdx)
  cmp    %rax,%rcx
  jne    L25
  add    $0x18,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nopw   0x0(%rax,%rax,1)
L24:
  lea    (%r12,%r14,1),%r15
  movsd  D17(%rip),%xmm2
  xor    %r13d,%r13d
  pxor   %xmm1,%xmm1
  add    %r15,%r14
  cs nopw 0x0(%rax,%rax,1)
L57:
  movapd %xmm1,%xmm5
  movapd %xmm2,%xmm4
  movapd %xmm1,%xmm3
  mov    %r13d,%edi
  movapd %xmm2,%xmm0
  mov    %r14,%r8
  mov    %r15,%rcx
  mov    %r12,%rdx
  mov    %rbp,%rsi
  add    $0x2,%r13d
  call   <btrfly@plt>
  mov    D17(%rip),%rax
  cmp    %ebx,%r13d
  pxor   %xmm1,%xmm1
  movq   %rax,%xmm2
  jl     L57
  add    $0x18,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nopl   0x0(%rax)
L44:
  mov    $0x8,%ebx
  mov    $0x4,%r15d
  jmp    L13
```

tool_calls: name: retrieve_data
arguments: data_tag: D17
datatype: f64

tool: D17: 1

assistant: ```c
void dfft(int n, int logn, double *a, double *w) {
  int i, l, j;
  double *v, *b, *c, *d;
  cft1st(n, a, w);
  i = 4;
  l = 8;
  for (; i <= logn / 2; i += 2, l *= 4)
    cftmd1(n, l, a, w);
  for (; i <= logn - 1; i += 2, l *= 4)
    cftmd2(n, l, a, w);
  v = w + 1;
  b = a + l;
  c = a + l + l;
  d = a + l + l + l;
  if ((l << 2) == n) {
#pragma mta use 100 streams
#pragma mta assert no dependence
    for (j = 0; j < l; j += 2)
      btrfly(j, 1.0, 0.0, 1.0, 0.0, 1.0, 0.0, a, b, c, d);
  } else {
#pragma mta use 100 streams
#pragma mta assert no dependence
    for (j = 0; j < l; j += 2) {
      double x0r = a[j];
      double x0i = a[j + 1];
      double x1r = b[j];
      double x1i = b[j + 1];
      a[j] = x0r + x1r;
      a[j + 1] = x0i + x1i;
      b[j] = x0r - x1r;
      b[j + 1] = x0i - x1i;
    }
  }
}
```