user: Converte this assembly snippet into its equivalent C code:

```asm
<dcsqb1>:
  endbr64
  push   %r15
  push   %r14
  lea    0x1(%rdi),%r14d
  push   %r13
  sar    %r14d
  mov    %rdx,%r13
  push   %r12
  mov    %edi,%r12d
  push   %rbp
  mov    %rcx,%rbp
  push   %rbx
  mov    %rsi,%rbx
  sub    $0x78,%rsp
  cmp    $0x2,%edi
  jle    L135
  lea    -0x3(%rdi),%ecx
  lea    0x8(%rsi),%rax
  xor    %edx,%edx
  shr    %ecx
  add    $0x1,%ecx
  nopl   0x0(%rax,%rax,1)
L15:
  movupd (%rax),%xmm0
  add    $0x1,%edx
  add    $0x10,%rax
  movapd %xmm0,%xmm1
  movapd %xmm0,%xmm2
  shufpd $0x1,%xmm0,%xmm1
  addpd  %xmm1,%xmm2
  subpd  %xmm1,%xmm0
  movsd  %xmm2,%xmm0
  movups %xmm0,-0x10(%rax)
  cmp    %ecx,%edx
  jb     L15
L135:
  movsd  (%rbx),%xmm0
  mov    %r12d,%eax
  and    $0x1,%eax
  addsd  %xmm0,%xmm0
  mov    %eax,0x48(%rsp)
  movsd  %xmm0,(%rbx)
  jne    L205
  movslq %r12d,%rax
  mov    %r8,%rcx
  mov    %rbp,%rdx
  mov    %rbx,%rsi
  mov    %rax,0x10(%rsp)
  lea    -0x8(%rbx,%rax,8),%rax
  mov    %r12d,%edi
  movsd  (%rax),%xmm0
  addsd  %xmm0,%xmm0
  movsd  %xmm0,(%rax)
  call   <__ogg_fdrfftb@plt>
  cmp    $0x1,%r14d
  jle    L200
L165:
  mov    0x10(%rsp),%rax
  mov    %r14d,%r10d
  lea    0x18(%rbp),%r9
  lea    0x8(%rbp),%r15
  lea    0x0(,%r10,8),%r8
  mov    %r9,0x30(%rsp)
  shl    $0x3,%rax
  lea    -0x10(%rax),%rsi
  lea    -0x8(%rax),%rdx
  lea    (%rbx,%rsi,1),%rdi
  lea    0x0(%rbp,%rdx,1),%r11
  mov    %rdx,0x58(%rsp)
  mov    %rdi,0x20(%rsp)
  lea    0x0(%rbp,%r8,1),%rdx
  lea    -0x1(%r14),%edi
  mov    %rdx,0x18(%rsp)
  mov    %edi,%edx
  lea    -0x18(%r13,%rax,1),%rcx
  neg    %rdx
  mov    %rsi,0x60(%rsp)
  shl    $0x3,%rdx
  mov    %r11,0x38(%rsp)
  mov    %r9,%r11
  lea    0x18(%rbx),%r9
  lea    (%rax,%rdx,1),%rsi
  mov    %rcx,0x28(%rsp)
  cmp    %r9,%r15
  lea    0x0(%rbp,%rsi,1),%rcx
  mov    %r9,0x50(%rsp)
  setae  %r9b
  mov    %rcx,0x40(%rsp)
  lea    0x8(%rbx),%rcx
  cmp    %r11,%rcx
  mov    %rcx,0x8(%rsp)
  setae  %cl
  mov    %edi,0x4(%rsp)
  lea    0x0(%rbp,%rax,1),%rdi
  or     %ecx,%r9d
  lea    0x10(%r13),%rcx
  cmp    %rcx,%r15
  mov    %rcx,0x68(%rsp)
  setae  %cl
  cmp    %r11,%r13
  setae  0x4f(%rsp)
  movzbl 0x4f(%rsp),%r11d
  or     %r11d,%ecx
  mov    0x38(%rsp),%r11
  and    %r9d,%ecx
  cmp    $0x2,%r14d
  setne  %r9b
  and    %r9d,%ecx
  mov    0x20(%rsp),%r9
  cmp    %r9,%r11
  setne  %r9b
  and    %ecx,%r9d
  cmp    0x28(%rsp),%r11
  mov    0x40(%rsp),%r11
  setne  %cl
  add    %rbx,%rax
  and    %r9d,%ecx
  cmp    %rax,%r15
  lea    (%rbx,%rsi,1),%r9
  setae  %al
  cmp    %r9,0x18(%rsp)
  setbe  %r9b
  or     %eax,%r9d
  lea    (%rbx,%r8,1),%rax
  and    %ecx,%r9d
  cmp    %rax,%r11
  setae  %al
  cmp    0x8(%rsp),%rdi
  setbe  %cl
  or     %ecx,%eax
  and    %r9d,%eax
  cmp    %rsi,%r8
  setle  %cl
  cmp    %rdi,%r15
  setae  %r8b
  or     %r8d,%ecx
  and    %eax,%ecx
  mov    %r13,%rax
  sub    %rdx,%rax
  cmp    %rax,%r11
  setae  %al
  cmp    %rdi,%r13
  setae  %dl
  or     %edx,%eax
  test   %al,%cl
  je     L179
  mov    0x58(%rsp),%rdx
  lea    -0x8(%r13,%rsi,1),%rax
  cmp    %rax,0x18(%rsp)
  setbe  %al
  add    %r13,%rdx
  cmp    %rdx,%r15
  setae  %dl
  or     %al,%dl
  je     L179
  mov    0x4(%rsp),%r9d
  mov    0x60(%rsp),%r11
  mov    %r13,%rax
  mov    %r15,%r8
  mov    0x20(%rsp),%rsi
  mov    0x28(%rsp),%rcx
  shr    %r9d
  add    %rbp,%r11
  mov    0x8(%rsp),%rdx
  sub    $0x1,%r9d
  mov    %r11,%rdi
  shl    $0x4,%r9
  add    0x68(%rsp),%r9
  nopw   0x0(%rax,%rax,1)
L42:
  movupd (%rsi),%xmm0
  movupd (%rax),%xmm1
  add    $0x10,%rax
  sub    $0x10,%rsi
  movupd (%rdx),%xmm5
  sub    $0x10,%rcx
  add    $0x10,%rdx
  add    $0x10,%r8
  shufpd $0x1,%xmm0,%xmm0
  mulpd  %xmm0,%xmm1
  movupd 0x10(%rcx),%xmm0
  sub    $0x10,%rdi
  shufpd $0x1,%xmm0,%xmm0
  mulpd  %xmm5,%xmm0
  addpd  %xmm1,%xmm0
  movups %xmm0,-0x10(%r8)
  movupd -0x10(%rax),%xmm0
  movupd -0x10(%rdx),%xmm6
  movupd 0x10(%rcx),%xmm1
  movupd 0x10(%rsi),%xmm2
  mulpd  %xmm6,%xmm0
  shufpd $0x1,%xmm1,%xmm1
  shufpd $0x1,%xmm2,%xmm2
  mulpd  %xmm2,%xmm1
  subpd  %xmm1,%xmm0
  shufpd $0x1,%xmm0,%xmm0
  movups %xmm0,0x10(%rdi)
  cmp    %r9,%rax
  jne    L42
  mov    0x4(%rsp),%edi
  mov    %r12d,%eax
  mov    %edi,%edx
  mov    %edi,%ecx
  and    $0xfffffffe,%edx
  or     $0x1,%ecx
  sub    %edx,%eax
  cmp    %edx,%edi
  je     L38
  sub    $0x1,%eax
  movslq %ecx,%rcx
  cltq
  lea    0x0(,%rcx,8),%rdx
  lea    0x0(,%rax,8),%rdi
  lea    -0x8(%r13,%rdx,1),%r8
  add    %rbx,%rdx
  lea    (%rbx,%rdi,1),%rsi
  lea    -0x8(%r13,%rdi,1),%rdi
  movsd  (%r8),%xmm0
  movsd  (%rdi),%xmm1
  mulsd  (%rsi),%xmm0
  mulsd  (%rdx),%xmm1
  addsd  %xmm1,%xmm0
  movsd  %xmm0,0x0(%rbp,%rcx,8)
  movsd  (%r8),%xmm0
  movsd  (%rdi),%xmm1
  mulsd  (%rdx),%xmm0
  mulsd  (%rsi),%xmm1
  subsd  %xmm1,%xmm0
  movsd  %xmm0,0x0(%rbp,%rax,8)
L38:
  mov    0x48(%rsp),%eax
  test   %eax,%eax
  je     L112
L58:
  mov    0x4(%rsp),%ecx
  mov    0x10(%rsp),%rax
  xor    %r9d,%r9d
  lea    0x0(,%r10,8),%rsi
  mov    0x8(%rsp),%r13
  mov    0x30(%rsp),%r11
  neg    %rcx
  cmp    $0x1,%r14d
  lea    0x0(,%rax,8),%rdi
  lea    0x8(,%rcx,8),%rcx
  lea    -0x8(%rdi),%r8
  cmovle %r9,%rcx
  mov    $0x10,%r9d
  lea    -0x10(%rdi),%rdx
  lea    0x0(%rbp,%rdx,1),%rax
  lea    (%rbx,%rdi,1),%r10
  add    %r8,%rcx
  cmp    $0x1,%r14d
  cmovle %r9,%rsi
  cmp    0x50(%rsp),%r15
  setae  %r9b
  cmp    %r11,%r13
  setae  %r11b
  or     %r9d,%r11d
  cmp    $0x2,%r14d
  setg   %r9b
  add    %rbx,%r8
  and    %r11d,%r9d
  cmp    %r8,%rax
  setne  %r8b
  and    %r8d,%r9d
  cmp    %rsi,%rcx
  setge  %r8b
  cmp    %r10,%r13
  setae  %r11b
  or     %r11d,%r8d
  lea    (%rbx,%rcx,1),%r11
  and    %r9d,%r8d
  lea    0x0(%rbp,%rsi,1),%r9
  cmp    %r9,%r11
  setae  %r9b
  cmp    %r10,%r15
  setae  %r10b
  or     %r10d,%r9d
  test   %r9b,%r8b
  je     L127
  add    %rbx,%rsi
  add    %rbp,%rcx
  cmp    %rcx,%rsi
  setbe  %cl
  add    %rbp,%rdi
  cmp    %rdi,%r13
  setae  %sil
  or     %sil,%cl
  je     L127
  cmp    $0x1,%r14d
  mov    $0x1,%edi
  mov    %r15,%rcx
  mov    %r13,%rsi
  cmovg  0x4(%rsp),%edi
  add    %rbx,%rdx
  mov    %edi,%r8d
  shr    %r8d
  sub    $0x1,%r8d
  shl    $0x4,%r8
  add    0x30(%rsp),%r8
  nopl   0x0(%rax)
L91:
  movupd (%rax),%xmm0
  movupd (%rcx),%xmm5
  add    $0x10,%rcx
  sub    $0x10,%rax
  add    $0x10,%rsi
  sub    $0x10,%rdx
  shufpd $0x1,%xmm0,%xmm0
  addpd  %xmm5,%xmm0
  movups %xmm0,-0x10(%rsi)
  movupd 0x10(%rax),%xmm1
  movupd -0x10(%rcx),%xmm0
  shufpd $0x1,%xmm1,%xmm1
  subpd  %xmm1,%xmm0
  shufpd $0x1,%xmm0,%xmm0
  movups %xmm0,0x10(%rdx)
  cmp    %r8,%rcx
  jne    L91
  mov    %edi,%edx
  mov    %edi,%eax
  and    $0xfffffffe,%edx
  or     $0x1,%eax
  sub    %edx,%r12d
  cmp    %edx,%edi
  je     L192
  sub    $0x1,%r12d
  cltq
  movslq %r12d,%r12
  lea    0x0(%rbp,%rax,8),%rcx
  lea    0x0(%rbp,%r12,8),%rdx
  movsd  (%rcx),%xmm0
  addsd  (%rdx),%xmm0
  movsd  %xmm0,(%rbx,%rax,8)
  movsd  (%rcx),%xmm0
  subsd  (%rdx),%xmm0
  movsd  %xmm0,(%rbx,%r12,8)
L192:
  movsd  (%rbx),%xmm0
  addsd  %xmm0,%xmm0
  movsd  %xmm0,(%rbx)
  add    $0x78,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nopl   0x0(%rax,%rax,1)
L205:
  mov    %r8,%rcx
  mov    %rbp,%rdx
  mov    %rbx,%rsi
  mov    %r12d,%edi
  call   <__ogg_fdrfftb@plt>
  movslq %r12d,%rax
  mov    %rax,0x10(%rsp)
  cmp    $0x1,%r14d
  jg     L165
  jmp    L192
  nopl   (%rax)
L112:
  movslq %r14d,%rdx
  shl    $0x3,%rdx
  lea    (%rbx,%rdx,1),%rax
  movsd  (%rax),%xmm0
  addsd  %xmm0,%xmm0
  mulsd  -0x8(%r13,%rdx,1),%xmm0
  movsd  %xmm0,(%rax)
  jmp    L58
L200:
  movslq %r14d,%rax
  shl    $0x3,%rax
  lea    (%rbx,%rax,1),%rdx
  movsd  (%rdx),%xmm0
  addsd  %xmm0,%xmm0
  mulsd  -0x8(%r13,%rax,1),%xmm0
  movsd  %xmm0,(%rdx)
  jmp    L192
  xchg   %ax,%ax
L127:
  mov    0x10(%rsp),%rax
  lea    -0x8(,%rax,8),%rdx
  mov    $0x1,%eax
  nopw   0x0(%rax,%rax,1)
L174:
  movsd  0x0(%rbp,%rax,8),%xmm0
  addsd  0x0(%rbp,%rdx,1),%xmm0
  movsd  %xmm0,(%rbx,%rax,8)
  movsd  0x0(%rbp,%rax,8),%xmm0
  add    $0x1,%rax
  subsd  0x0(%rbp,%rdx,1),%xmm0
  movsd  %xmm0,(%rbx,%rdx,1)
  sub    $0x8,%rdx
  cmp    %eax,%r14d
  jg     L174
  jmp    L192
  nopl   0x0(%rax)
L179:
  mov    0x10(%rsp),%rax
  movslq %r14d,%rcx
  lea    -0x8(,%rax,8),%rdx
  mov    $0x1,%eax
  nopl   (%rax)
L105:
  movsd  -0x8(%r13,%rax,8),%xmm0
  movsd  -0x8(%r13,%rdx,1),%xmm1
  mulsd  (%rbx,%rdx,1),%xmm0
  mulsd  (%rbx,%rax,8),%xmm1
  addsd  %xmm1,%xmm0
  movsd  %xmm0,0x0(%rbp,%rax,8)
  movsd  -0x8(%r13,%rax,8),%xmm0
  movsd  -0x8(%r13,%rdx,1),%xmm1
  mulsd  (%rbx,%rax,8),%xmm0
  add    $0x1,%rax
  mulsd  (%rbx,%rdx,1),%xmm1
  subsd  %xmm1,%xmm0
  movsd  %xmm0,0x0(%rbp,%rdx,1)
  sub    $0x8,%rdx
  cmp    %rcx,%rax
  jne    L105
  jmp    L38
```

assistant: ```c
void dcsqb1(int n, double *x, double *w, double *xh, int *ifac) {
  int modn, i, k, kc;
  int np2, ns2;
  double xim1;
  ns2 = (n + 1) >> 1;
  np2 = n;
  for (i = 2; i < n; i += 2) {
    xim1 = x[i - 1] + x[i];
    x[i] -= x[i - 1];
    x[i - 1] = xim1;
  }
  x[0] += x[0];
  modn = n % 2;
  if (modn == 0)
    x[n - 1] += x[n - 1];
  __ogg_fdrfftb(n, x, xh, ifac);
  kc = np2;
  for (k = 1; k < ns2; k++) {
    kc--;
    xh[k] = w[k - 1] * x[kc] + w[kc - 1] * x[k];
    xh[kc] = w[k - 1] * x[k] - w[kc - 1] * x[kc];
  }
  if (modn == 0)
    x[ns2] = w[ns2 - 1] * (x[ns2] + x[ns2]);
  kc = np2;
  for (k = 1; k < ns2; k++) {
    kc--;
    x[k] = xh[k] + xh[kc];
    x[kc] = xh[k] - xh[kc];
  }
  x[0] += x[0];
}
```