bool rayHitsAABB(vec3f a, vec3f b, vec3f pos, vec3f dir) {
  xmm[4] = dir;
  xmm[5] = pos;
  xmm[6] = a;
  xmm[7] = b;
  int i = 1 << 31;
  asm "movd (%esp), %xmm3";
  asm `shufps $0, %xmm3, %xmm3`;
  asm "movaps %xmm4, %xmm2";
  asm "andps %xmm3, %xmm2"; // select sign bits of dir
  asm "xorps %xmm2, %xmm4"; // flip signs where negative
  asm "xorps %xmm2, %xmm5";
  asm "xorps %xmm2, %xmm6";
  asm "xorps %xmm2, %xmm7";
  asm "movaps %xmm6, %xmm2";
  asm "movaps %xmm7, %xmm3";
  asm "minps %xmm3, %xmm6"; // a = min(a, b);
  asm "maxps %xmm2, %xmm7"; // b = max(a, b);
  // pretend ray starts at origin
  dir = xmm[4];
  pos = xmm[5];
  a   = xmm[6];
  b   = xmm[7];

  a -= pos;
  b -= pos;