user: 请将以下的汇编代码转换成C语言代码：

```asm
<FFT>:
  endbr64
  test   %edx,%edx
  jle    L27
  push   %r15
  mov    %edx,%eax
  mov    %rdi,%r10
  mov    %rsi,%r11
  push   %r14
  push   %r13
  push   %r12
  mov    %edx,%r12d
  xor    %edx,%edx
  push   %rbp
  mov    %rcx,%rbp
  push   %rbx
  cs nopw 0x0(%rax,%rax,1)
L89:
  sar    %eax
  mov    %edx,%ecx
  lea    0x1(%rdx),%edx
  jne    L89
  mov    %r12d,%esi
  mov    %r12d,%r15d
  mov    %ecx,-0x4(%rsp)
  sar    %esi
  sub    $0x1,%r15d
  je     L65
  lea    -0x2(%r12),%r8d
  xor    %edx,%edx
  mov    $0x1,%ecx
  add    $0x1,%r8
  nopl   0x0(%rax,%rax,1)
L69:
  mov    %esi,%eax
  cmp    %esi,%edx
  jl     L105
  cs nopw 0x0(%rax,%rax,1)
L9:
  sub    %eax,%edx
  sar    %eax
  cmp    %eax,%edx
  jge    L9
L105:
  add    %eax,%edx
  cmp    %rcx,%r8
  je     L65
  cmp    %ecx,%edx
  jle    L116
  movslq %edx,%rax
  movsd  (%r10,%rcx,8),%xmm1
  movsd  (%r11,%rcx,8),%xmm0
  shl    $0x3,%rax
  lea    (%r10,%rax,1),%rdi
  add    %r11,%rax
  movsd  (%rdi),%xmm2
  movsd  %xmm2,(%r10,%rcx,8)
  movsd  (%rax),%xmm2
  movsd  %xmm2,(%r11,%rcx,8)
  movsd  %xmm1,(%rdi)
  movsd  %xmm0,(%rax)
L116:
  add    $0x1,%rcx
  jmp    L69
L65:
  mov    -0x4(%rsp),%eax
  movl   $0x0,-0x8(%rsp)
  mov    $0x1,%r13d
  movq   D5(%rip),%xmm4
  test   %eax,%eax
  je     L56
  nopl   0x0(%rax)
L20:
  mov    %r12d,%eax
  mov    %r13d,%ebx
  add    %r13d,%r13d
  xor    %r14d,%r14d
  cltd
  movl   $0x0,-0x10(%rsp)
  idiv   %r13d
  mov    %eax,-0xc(%rsp)
  test   %eax,%eax
  je     L126
  nopl   0x0(%rax)
L12:
  mov    -0x10(%rsp),%eax
  xor    %r9d,%r9d
  xor    %edi,%edi
  nopl   0x0(%rax)
L63:
  cltd
  add    $0x1,%r9d
  idiv   %r15d
  mov    %edi,%eax
  add    %r12d,%edi
  mov    %edx,%esi
  cltd
  idiv   %r13d
  lea    (%rsi,%rbx,1),%ecx
  movslq %ecx,%rcx
  shl    $0x3,%rcx
  lea    (%r10,%rcx,1),%r8
  add    %r11,%rcx
  movsd  (%r8),%xmm2
  movsd  (%rcx),%xmm0
  movapd %xmm2,%xmm1
  movapd %xmm0,%xmm6
  add    %eax,%eax
  cltq
  movsd  0x8(%rbp,%rax,8),%xmm3
  movsd  0x0(%rbp,%rax,8),%xmm5
  movslq %esi,%rax
  shl    $0x3,%rax
  mulsd  %xmm5,%xmm1
  xorpd  %xmm4,%xmm3
  lea    (%r10,%rax,1),%rdx
  add    %r11,%rax
  mulsd  %xmm3,%xmm6
  mulsd  %xmm3,%xmm2
  mulsd  %xmm5,%xmm0
  subsd  %xmm6,%xmm1
  addsd  %xmm2,%xmm0
  movsd  (%rdx),%xmm2
  subsd  %xmm1,%xmm2
  movsd  %xmm2,(%r8)
  movsd  (%rax),%xmm2
  subsd  %xmm0,%xmm2
  movsd  %xmm2,(%rcx)
  addsd  (%rdx),%xmm1
  movsd  %xmm1,(%rdx)
  addsd  (%rax),%xmm0
  movsd  %xmm0,(%rax)
  lea    0x1(%rsi),%eax
  cmp    %ebx,%r9d
  jne    L63
  add    %r13d,-0x10(%rsp)
  add    $0x1,%r14d
  cmp    %r14d,-0xc(%rsp)
  jne    L12
L126:
  addl   $0x1,-0x8(%rsp)
  mov    -0x8(%rsp),%eax
  cmp    -0x4(%rsp),%eax
  jne    L20
L56:
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L27:
  ret
```

tool_calls: name: unpack_data
arguments: tag: D5
datatype: byte[8]

tool: {"D5": [0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x80]}

assistant: ```c
void FFT(double *x, double *y, int n, double w[]) {
  int m, i, j, k, nbits;
  double tempx, tempy;
  m = 0;
  i = n;
  while (i > 0) {
    i /= 2;
    m++;
  }
  m -= 1;
  nbits = n >> 1;
  j = 0;
  for (i = 0; i < n - 1; i++) {
    if (i < j) {
      tempx = x[i];
      tempy = y[i];
      x[i] = x[j];
      y[i] = y[j];
      x[j] = tempx;
      y[j] = tempy;
    }
    k = nbits;
    while (k <= j) {
      j -= k;
      k >>= 1;
    }
    j += k;
  }
  int mj, term_i, stride_i, mi, j2, count2;
  double u1, u2, t1, t2;
  mj = 1;
  stride_i = n / (4 * mj);
  for (k = 0; k < m; k++) {
    mi = 2 * mj;
    term_i = n / mi;
    for (i = 0; i < term_i; i++) {
      count2 = 0;
      for (j = i * mi; count2 < mj; j++, count2++) {
        j %= (n - 1);
        j2 = (j + mj);
        int temp = count2 * n / mi;
        u1 = w[temp * 2 + 0];
        u2 = -w[temp * 2 + 1];
        t1 = u1 * x[j2] - u2 * y[j2];
        t2 = u1 * y[j2] + u2 * x[j2];
        x[j2] = x[j] - t1;
        y[j2] = y[j] - t2;
        x[j] += t1;
        y[j] += t2;
      }
    }
    stride_i /= 2;
    mj *= 2;
  }
  return;
}
```