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

```asm
<bitrv2>:
  endbr64
  push   %r15
  mov    %rsi,%r10
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  movl   $0x0,(%rsi)
  cmp    $0x8,%edi
  jle    L83
  mov    %edi,%r8d
  mov    $0x1,%ecx
  lea    0x4(%rsi),%r9
  nopl   0x0(%rax)
L209:
  sar    %r8d
  test   %ecx,%ecx
  jle    L84
  movslq %ecx,%rsi
  lea    -0x1(%rcx),%r11d
  lea    0x0(,%rsi,4),%rdi
  lea    -0x4(%rdi),%rax
  cmp    $0x8,%rax
  jbe    L169
  cmp    $0x2,%r11d
  jbe    L169
  mov    %ecx,%esi
  movd   %r8d,%xmm2
  add    %r10,%rdi
  xor    %eax,%eax
  shr    $0x2,%esi
  pshufd $0x0,%xmm2,%xmm1
  shl    $0x4,%rsi
  nopw   0x0(%rax,%rax,1)
L66:
  movdqu (%r10,%rax,1),%xmm0
  paddd  %xmm1,%xmm0
  movups %xmm0,(%rdi,%rax,1)
  add    $0x10,%rax
  cmp    %rax,%rsi
  jne    L66
  mov    %ecx,%eax
  and    $0xfffffffc,%eax
  test   $0x3,%cl
  je     L84
  mov    %eax,%r11d
  lea    (%rcx,%rax,1),%esi
  mov    (%r10,%r11,4),%ebx
  movslq %esi,%rsi
  lea    0x0(,%r11,4),%rdi
  add    %r8d,%ebx
  mov    %ebx,(%r10,%rsi,4)
  lea    0x1(%rax),%esi
  cmp    %esi,%ecx
  jle    L84
  mov    0x4(%r10,%rdi,1),%r11d
  add    %ecx,%esi
  add    $0x2,%eax
  movslq %esi,%rsi
  add    %r8d,%r11d
  mov    %r11d,(%r10,%rsi,4)
  cmp    %eax,%ecx
  jle    L84
  mov    0x8(%r10,%rdi,1),%esi
  add    %ecx,%eax
  cltq
  add    %r8d,%esi
  mov    %esi,(%r10,%rax,4)
L84:
  mov    %ecx,%eax
  lea    (%rcx,%rcx,1),%r13d
  shl    $0x4,%eax
  cmp    %r8d,%eax
  jge    L195
L156:
  mov    %r13d,%ecx
  jmp    L209
  nopw   0x0(%rax,%rax,1)
L169:
  mov    %r10,%rax
  lea    (%r9,%r11,4),%r11
  nop
L138:
  mov    (%rax),%edi
  add    %r8d,%edi
  mov    %edi,(%rax,%rsi,4)
  add    $0x4,%rax
  cmp    %rax,%r11
  jne    L138
  mov    %ecx,%eax
  lea    (%rcx,%rcx,1),%r13d
  shl    $0x4,%eax
  cmp    %r8d,%eax
  jl     L156
  nop
L195:
  lea    0x0(,%rcx,4),%r11d
  je     L179
  cmp    $0x1,%r13d
  jle    L7
  lea    0x4(%r10),%rbx
  mov    %r11d,%r12d
  mov    $0x2,%r9d
  movslq %r11d,%rbp
  nopl   0x0(%rax)
L171:
  movslq (%rbx),%rax
  mov    %r10,%rdi
  lea    (%rdx,%rax,4),%rsi
  add    %rbp,%rax
  lea    (%rdx,%rax,4),%rcx
  nopl   0x0(%rax)
L50:
  mov    (%rdi),%eax
  mov    (%rsi),%r13
  add    $0x4,%rdi
  add    $0x8,%rsi
  add    $0x8,%rcx
  add    %r9d,%eax
  movslq %eax,%r8
  add    %r11d,%eax
  lea    (%rdx,%r8,4),%r8
  cltq
  mov    (%r8),%r14
  lea    (%rdx,%rax,4),%rax
  mov    %r14,-0x8(%rsi)
  mov    %r13,(%r8)
  mov    -0x8(%rcx),%r8
  mov    (%rax),%r13
  mov    %r13,-0x8(%rcx)
  mov    %r8,(%rax)
  cmp    %rbx,%rdi
  jne    L50
  add    $0x2,%r9d
  add    $0x4,%rbx
  cmp    %r9d,%r12d
  jne    L171
L7:
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L179:
  test   %r13d,%r13d
  jle    L7
  shl    $0x3,%ecx
L197:
  movslq %r11d,%rax
  xor    %edi,%edi
  mov    %r13d,-0x2c(%rsp)
  xor    %r14d,%r14d
  lea    (%rax,%rax,1),%rbx
  mov    %rax,-0x28(%rsp)
  mov    %edi,%r13d
  mov    %rbx,-0x20(%rsp)
  add    %rax,%rbx
  lea    0x8(%rdx),%rax
  mov    %rbx,-0x18(%rsp)
  mov    %rax,-0x10(%rsp)
L24:
  lea    (%r11,%r14,1),%eax
  add    (%r10,%r14,2),%eax
  add    $0x1,%r13d
  movslq %eax,%rsi
  add    %r11d,%eax
  cltq
  lea    (%rdx,%rsi,4),%rsi
  lea    (%rdx,%rax,4),%rax
  mov    (%rsi),%rdi
  mov    (%rax),%r8
  mov    %r8,(%rsi)
  mov    %rdi,(%rax)
  cmp    %r13d,-0x2c(%rsp)
  jle    L7
  movslq 0x4(%r10,%r14,2),%rax
  mov    -0x28(%rsp),%rdi
  lea    0x0(%r13,%r13,1),%r12d
  mov    %r10,%rbx
  mov    -0x10(%rsp),%r15
  add    %rax,%rdi
  lea    (%rdx,%rax,4),%rsi
  lea    (%rdx,%rdi,4),%r9
  mov    -0x20(%rsp),%rdi
  add    %rax,%rdi
  lea    (%rdx,%rdi,4),%r8
  mov    -0x18(%rsp),%rdi
  add    %rax,%rdi
  add    %r14,%rax
  lea    (%rdx,%rdi,4),%rdi
  lea    (%r15,%rax,4),%rbp
L46:
  mov    (%rbx),%eax
  movq   (%rsi),%xmm0
  add    $0x8,%rsi
  add    $0x4,%rbx
  add    $0x8,%r9
  add    $0x8,%r8
  add    $0x8,%rdi
  add    %r12d,%eax
  movslq %eax,%r15
  add    %ecx,%eax
  lea    (%rdx,%r15,4),%r15
  movq   (%r15),%xmm1
  movlps %xmm1,-0x8(%rsi)
  movlps %xmm0,(%r15)
  movslq %eax,%r15
  movq   -0x8(%r9),%xmm0
  sub    %r11d,%eax
  lea    (%rdx,%r15,4),%r15
  movq   (%r15),%xmm1
  movlps %xmm1,-0x8(%r9)
  movlps %xmm0,(%r15)
  movslq %eax,%r15
  add    %ecx,%eax
  movq   -0x8(%r8),%xmm0
  lea    (%rdx,%r15,4),%r15
  cltq
  movq   (%r15),%xmm1
  lea    (%rdx,%rax,4),%rax
  movlps %xmm1,-0x8(%r8)
  movlps %xmm0,(%r15)
  mov    -0x8(%rdi),%r15
  movq   (%rax),%xmm0
  movlps %xmm0,-0x8(%rdi)
  mov    %r15,(%rax)
  cmp    %rsi,%rbp
  jne    L46
  add    $0x2,%r14
  jmp    L24
L83:
  jne    L7
  mov    $0x4,%ecx
  mov    $0x1,%r13d
  mov    $0x2,%r11d
  jmp    L197
```

assistant: ```c
void bitrv2(int n, int *ip, float *a) {
  int j, j1, k, k1, l, m, m2;
  float xr, xi, yr, yi;
  ip[0] = 0;
  l = n;
  m = 1;
  while ((m << 3) < l) {
    l >>= 1;
    for (j = 0; j < m; j++) {
      ip[m + j] = ip[j] + l;
    }
    m <<= 1;
  }
  m2 = 2 * m;
  if ((m << 3) == l) {
    for (k = 0; k < m; k++) {
      for (j = 0; j < k; j++) {
        j1 = 2 * j + ip[k];
        k1 = 2 * k + ip[j];
        xr = a[j1];
        xi = a[j1 + 1];
        yr = a[k1];
        yi = a[k1 + 1];
        a[j1] = yr;
        a[j1 + 1] = yi;
        a[k1] = xr;
        a[k1 + 1] = xi;
        j1 += m2;
        k1 += 2 * m2;
        xr = a[j1];
        xi = a[j1 + 1];
        yr = a[k1];
        yi = a[k1 + 1];
        a[j1] = yr;
        a[j1 + 1] = yi;
        a[k1] = xr;
        a[k1 + 1] = xi;
        j1 += m2;
        k1 -= m2;
        xr = a[j1];
        xi = a[j1 + 1];
        yr = a[k1];
        yi = a[k1 + 1];
        a[j1] = yr;
        a[j1 + 1] = yi;
        a[k1] = xr;
        a[k1 + 1] = xi;
        j1 += m2;
        k1 += 2 * m2;
        xr = a[j1];
        xi = a[j1 + 1];
        yr = a[k1];
        yi = a[k1 + 1];
        a[j1] = yr;
        a[j1 + 1] = yi;
        a[k1] = xr;
        a[k1 + 1] = xi;
      }
      j1 = 2 * k + m2 + ip[k];
      k1 = j1 + m2;
      xr = a[j1];
      xi = a[j1 + 1];
      yr = a[k1];
      yi = a[k1 + 1];
      a[j1] = yr;
      a[j1 + 1] = yi;
      a[k1] = xr;
      a[k1 + 1] = xi;
    }
  } else {
    for (k = 1; k < m; k++) {
      for (j = 0; j < k; j++) {
        j1 = 2 * j + ip[k];
        k1 = 2 * k + ip[j];
        xr = a[j1];
        xi = a[j1 + 1];
        yr = a[k1];
        yi = a[k1 + 1];
        a[j1] = yr;
        a[j1 + 1] = yi;
        a[k1] = xr;
        a[k1 + 1] = xi;
        j1 += m2;
        k1 += m2;
        xr = a[j1];
        xi = a[j1 + 1];
        yr = a[k1];
        yi = a[k1 + 1];
        a[j1] = yr;
        a[j1 + 1] = yi;
        a[k1] = xr;
        a[k1 + 1] = xi;
      }
    }
  }
}
```