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

```asm
<project_r>:
  endbr64
  lea    (%rsi,%rdi,2),%eax
  mov    %edx,%r10d
  mov    %esi,%r11d
  lea    (%rax,%rax,2),%r9d
  lea    (%r9,%rdi,1),%edx
  add    %edx,%edx
  lea    (%rdx,%rsi,1),%eax
  add    %eax,%eax
  cltq
  movsd  (%r8,%rax,8),%xmm2
  movsd  0x8(%r8,%rax,8),%xmm3
  lea    (%rcx,%r10,2),%eax
  lea    (%rax,%rax,2),%r10d
  lea    (%r10,%rdi,1),%eax
  add    %eax,%eax
  lea    (%rax,%rsi,1),%ecx
  add    %ecx,%ecx
  movslq %ecx,%rcx
  movsd  (%r8,%rcx,8),%xmm4
  movsd  0x8(%r8,%rcx,8),%xmm5
  lea    0x1(%rsi),%ecx
  cmp    $0x1,%ecx
  jg     L12
  lea    (%rax,%rcx,1),%esi
  neg    %r11d
  add    %edx,%ecx
  lea    (%rsi,%rsi,1),%eax
  movslq %esi,%rsi
  movslq %ecx,%rcx
  add    %rsi,%r11
  cltq
  neg    %rsi
  shl    $0x4,%rcx
  shl    $0x4,%r11
  lea    (%r8,%rax,8),%rax
  shl    $0x4,%rsi
  lea    0x10(%r8,%r11,1),%r11
  nopl   0x0(%rax,%rax,1)
L45:
  movsd  (%rax),%xmm8
  movsd  0x8(%rax),%xmm0
  movapd %xmm2,%xmm1
  movapd %xmm3,%xmm9
  lea    (%rsi,%rax,1),%rdx
  add    $0x10,%rax
  mulsd  %xmm0,%xmm9
  movsd  (%rdx,%rcx,1),%xmm6
  movsd  0x8(%rdx,%rcx,1),%xmm7
  mulsd  %xmm8,%xmm1
  mulsd  %xmm2,%xmm0
  mulsd  %xmm3,%xmm8
  subsd  %xmm9,%xmm1
  movapd %xmm4,%xmm9
  mulsd  %xmm6,%xmm9
  addsd  %xmm8,%xmm0
  mulsd  %xmm5,%xmm6
  subsd  %xmm9,%xmm1
  movapd %xmm5,%xmm9
  mulsd  %xmm7,%xmm9
  mulsd  %xmm4,%xmm7
  addsd  %xmm9,%xmm1
  subsd  %xmm7,%xmm0
  movsd  %xmm1,-0x10(%rax)
  subsd  %xmm6,%xmm0
  movsd  %xmm0,-0x8(%rax)
  cmp    %rax,%r11
  jne    L45
L12:
  add    $0x1,%edi
  cmp    $0x2,%edi
  jg     L6
  lea    (%r10,%rdi,1),%eax
  add    %edi,%r9d
  lea    (%rax,%rax,1),%esi
  movslq %r9d,%r9
  cltq
  movslq %esi,%rdx
  sub    %rax,%r9
  shl    $0x4,%rdx
  shl    $0x5,%r9
  lea    0x20(%r8,%rdx,1),%rcx
  lea    -0x20(%r9),%rdi
  lea    0x6(%r10,%r10,1),%r8d
  nopw   0x0(%rax,%rax,1)
L21:
  lea    (%rdi,%rcx,1),%rdx
  lea    -0x20(%rcx),%rax
L29:
  movsd  (%rax),%xmm8
  movsd  0x8(%rax),%xmm0
  movapd %xmm2,%xmm1
  movapd %xmm3,%xmm9
  movsd  (%rdx),%xmm6
  movsd  0x8(%rdx),%xmm7
  add    $0x10,%rax
  add    $0x10,%rdx
  mulsd  %xmm0,%xmm9
  mulsd  %xmm8,%xmm1
  mulsd  %xmm2,%xmm0
  mulsd  %xmm3,%xmm8
  subsd  %xmm9,%xmm1
  movapd %xmm4,%xmm9
  mulsd  %xmm6,%xmm9
  addsd  %xmm8,%xmm0
  mulsd  %xmm5,%xmm6
  subsd  %xmm9,%xmm1
  movapd %xmm5,%xmm9
  mulsd  %xmm7,%xmm9
  mulsd  %xmm4,%xmm7
  addsd  %xmm9,%xmm1
  subsd  %xmm7,%xmm0
  movsd  %xmm1,-0x10(%rax)
  subsd  %xmm6,%xmm0
  movsd  %xmm0,-0x8(%rax)
  cmp    %rax,%rcx
  jne    L29
  add    $0x2,%esi
  add    $0x20,%rcx
  cmp    %esi,%r8d
  jne    L21
L6:
  ret
```

assistant: ```c
void project_r(int a, int i, int b, int j, double r[]) {
  int c, k;
  double xi, yi, xj, yj;
  xi = (&((r)[2 * ((i) + 2 * ((a) + 3 * ((i) + 2 * (a))))]))[0];
  yi = (&((r)[2 * ((i) + 2 * ((a) + 3 * ((i) + 2 * (a))))]))[1];
  xj = (&((r)[2 * ((i) + 2 * ((a) + 3 * ((j) + 2 * (b))))]))[0];
  yj = (&((r)[2 * ((i) + 2 * ((a) + 3 * ((j) + 2 * (b))))]))[1];
  for (c = a, k = i + 1; k < 2; k++) {
    double zi = (&((r)[2 * ((k) + 2 * ((c) + 3 * ((i) + 2 * (a))))]))[0];
    double ti = (&((r)[2 * ((k) + 2 * ((c) + 3 * ((i) + 2 * (a))))]))[1];
    double zj = (&((r)[2 * ((k) + 2 * ((c) + 3 * ((j) + 2 * (b))))]))[0];
    double tj = (&((r)[2 * ((k) + 2 * ((c) + 3 * ((j) + 2 * (b))))]))[1];
    (&((r)[2 * ((k) + 2 * ((c) + 3 * ((j) + 2 * (b))))]))[0] = xi * zj - yi * tj - xj * zi + yj * ti;
    (&((r)[2 * ((k) + 2 * ((c) + 3 * ((j) + 2 * (b))))]))[1] = xi * tj + yi * zj - xj * ti - yj * zi;
  }
  for (c = a + 1; c < 3; c++) {
    for (k = 0; k < 2; k++) {
      double zi = (&((r)[2 * ((k) + 2 * ((c) + 3 * ((i) + 2 * (a))))]))[0];
      double ti = (&((r)[2 * ((k) + 2 * ((c) + 3 * ((i) + 2 * (a))))]))[1];
      double zj = (&((r)[2 * ((k) + 2 * ((c) + 3 * ((j) + 2 * (b))))]))[0];
      double tj = (&((r)[2 * ((k) + 2 * ((c) + 3 * ((j) + 2 * (b))))]))[1];
      (&((r)[2 * ((k) + 2 * ((c) + 3 * ((j) + 2 * (b))))]))[0] = xi * zj - yi * tj - xj * zi + yj * ti;
      (&((r)[2 * ((k) + 2 * ((c) + 3 * ((j) + 2 * (b))))]))[1] = xi * tj + yi * zj - xj * ti - yj * zi;
    }
  }
}
```