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

```asm
<bitrv2>:
  endbr64
  push   %r15
  mov    %rdx,%rax
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  mov    %rsi,%rbp
  push   %rbx
  movl   $0x0,(%rsi)
  cmp    $0x8,%edi
  jle    L125
  mov    $0x1,%r8d
  lea    0x4(%rsi),%r10
  nopl   (%rax)
L52:
  sar    %edi
  test   %r8d,%r8d
  jle    L136
  lea    -0x1(%r8),%ecx
  mov    %rbp,%rdx
  movslq %r8d,%rsi
  lea    (%r10,%rcx,4),%r9
  nopl   (%rax)
L77:
  mov    (%rdx),%ecx
  add    %edi,%ecx
  mov    %ecx,(%rdx,%rsi,4)
  add    $0x4,%rdx
  cmp    %rdx,%r9
  jne    L77
L136:
  mov    %r8d,%edx
  lea    (%r8,%r8,1),%r12d
  shl    $0x4,%edx
  cmp    %edi,%edx
  jge    L147
  mov    %r12d,%r8d
  jmp    L52
  nopl   0x0(%rax,%rax,1)
L147:
  lea    0x0(,%r8,4),%r10d
  je     L139
  cmp    $0x1,%r12d
  jle    L5
  lea    0x4(%rbp),%r11
  mov    %r10d,%r12d
  mov    $0x2,%r9d
  movslq %r10d,%rbx
  nopl   0x0(%rax,%rax,1)
L112:
  movslq (%r11),%rdx
  mov    %rbp,%r8
  lea    (%rax,%rdx,4),%rsi
  add    %rbx,%rdx
  lea    (%rax,%rdx,4),%rcx
  nopl   0x0(%rax)
L94:
  mov    (%r8),%edx
  movss  (%rsi),%xmm1
  add    $0x4,%r8
  add    $0x8,%rsi
  movss  -0x4(%rsi),%xmm0
  add    $0x8,%rcx
  add    %r9d,%edx
  movslq %edx,%rdi
  add    %r10d,%edx
  shl    $0x2,%rdi
  movslq %edx,%rdx
  lea    (%rax,%rdi,1),%r13
  lea    0x4(%rax,%rdi,1),%rdi
  shl    $0x2,%rdx
  movss  (%rdi),%xmm2
  movss  0x0(%r13),%xmm3
  movss  %xmm2,-0x4(%rsi)
  movss  %xmm3,-0x8(%rsi)
  movss  %xmm1,0x0(%r13)
  movss  %xmm0,(%rdi)
  lea    (%rax,%rdx,1),%rdi
  lea    0x4(%rax,%rdx,1),%rdx
  movss  -0x8(%rcx),%xmm1
  movss  (%rdi),%xmm3
  movss  (%rdx),%xmm2
  movss  -0x4(%rcx),%xmm0
  movss  %xmm3,-0x8(%rcx)
  movss  %xmm2,-0x4(%rcx)
  movss  %xmm1,(%rdi)
  movss  %xmm0,(%rdx)
  cmp    %r8,%r11
  jne    L94
  add    $0x2,%r9d
  add    $0x4,%r11
  cmp    %r9d,%r12d
  jne    L112
L5:
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L139:
  test   %r12d,%r12d
  jle    L5
  mov    0x0(%rbp),%ebx
  shl    $0x3,%r8d
  mov    %ebx,-0x18(%rsp)
L98:
  movslq %r10d,%rbx
  mov    %rbp,-0x8(%rsp)
  mov    %rbp,%r11
  xor    %r13d,%r13d
  mov    %rbx,-0x10(%rsp)
  lea    (%rax,%rbx,8),%rdi
  mov    -0x18(%rsp),%ebx
  mov    %r12d,-0x14(%rsp)
  mov    %r10d,%r12d
L17:
  add    %r12d,%ebx
  add    $0x1,%r13d
  movslq %ebx,%rdx
  add    %r10d,%ebx
  shl    $0x2,%rdx
  lea    (%rax,%rdx,1),%rcx
  lea    0x4(%rax,%rdx,1),%rsi
  movslq %ebx,%rdx
  shl    $0x2,%rdx
  movss  (%rcx),%xmm1
  movss  (%rsi),%xmm0
  lea    (%rax,%rdx,1),%r9
  lea    0x4(%rax,%rdx,1),%rdx
  movss  (%r9),%xmm3
  movss  (%rdx),%xmm2
  movss  %xmm3,(%rcx)
  movss  %xmm2,(%rsi)
  movss  %xmm1,(%r9)
  movss  %xmm0,(%rdx)
  cmp    %r13d,-0x14(%rsp)
  jle    L5
  movslq 0x4(%r11),%rcx
  mov    -0x8(%rsp),%r9
  lea    0x0(%r13,%r13,1),%ebp
  mov    -0x18(%rsp),%edx
  mov    %rcx,%rbx
  lea    0x0(,%rcx,4),%rsi
  add    -0x10(%rsp),%rcx
  shl    $0x2,%rcx
  jmp    L4
  nop
L34:
  mov    0x4(%r9),%edx
  add    $0x8,%rcx
  add    $0x4,%r9
L4:
  add    %ebp,%edx
  movss  (%rax,%rsi,1),%xmm1
  movss  0x4(%rax,%rsi,1),%xmm0
  movslq %edx,%r14
  add    %r8d,%edx
  shl    $0x2,%r14
  lea    (%rax,%r14,1),%r15
  lea    0x4(%rax,%r14,1),%r14
  movss  (%r15),%xmm3
  movss  (%r14),%xmm2
  movss  %xmm3,(%rax,%rsi,1)
  movss  %xmm2,0x4(%rax,%rsi,1)
  movss  %xmm1,(%r15)
  movss  %xmm0,(%r14)
  movslq %edx,%r14
  movss  (%rax,%rcx,1),%xmm1
  movss  0x4(%rax,%rcx,1),%xmm0
  shl    $0x2,%r14
  sub    %r10d,%edx
  lea    (%rax,%r14,1),%r15
  lea    0x4(%rax,%r14,1),%r14
  movss  (%r15),%xmm3
  movss  (%r14),%xmm2
  movss  %xmm3,(%rax,%rcx,1)
  movss  %xmm2,0x4(%rax,%rcx,1)
  movss  %xmm1,(%r15)
  movss  %xmm0,(%r14)
  movslq %edx,%r14
  add    %r8d,%edx
  movss  (%rdi,%rsi,1),%xmm1
  shl    $0x2,%r14
  movss  0x4(%rdi,%rsi,1),%xmm0
  movslq %edx,%rdx
  lea    (%rax,%r14,1),%r15
  lea    0x4(%rax,%r14,1),%r14
  shl    $0x2,%rdx
  movss  (%r14),%xmm2
  movss  (%r15),%xmm3
  movss  %xmm2,0x4(%rdi,%rsi,1)
  movss  %xmm3,(%rdi,%rsi,1)
  add    $0x8,%rsi
  movss  %xmm1,(%r15)
  movss  %xmm0,(%r14)
  lea    (%rax,%rdx,1),%r14
  lea    0x4(%rax,%rdx,1),%rdx
  movss  (%rdi,%rcx,1),%xmm1
  movss  (%r14),%xmm3
  movss  (%rdx),%xmm2
  movss  0x4(%rdi,%rcx,1),%xmm0
  movss  %xmm3,(%rdi,%rcx,1)
  movss  %xmm2,0x4(%rdi,%rcx,1)
  movss  %xmm1,(%r14)
  movss  %xmm0,(%rdx)
  cmp    %r11,%r9
  jne    L34
  add    $0x2,%r12d
  add    $0x4,%r11
  jmp    L17
L125:
  jne    L5
  movl   $0x0,-0x18(%rsp)
  mov    $0x4,%r8d
  mov    $0x1,%r12d
  mov    $0x2,%r10d
  jmp    L98
```

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;
      }
    }
  }
}
```