double erfinv()

in absl/random/internal/distribution_test_util.cc [110:185]

• 75 lines of code
• 3 McCabe index (conditional complexity)

double erfinv(double x) {
#if !defined(__EMSCRIPTEN__)
  using std::fma;
#endif

  double w = 0.0;
  double p = 0.0;
  w = -std::log((1.0 - x) * (1.0 + x));
  if (w < 6.250000) {
    w = w - 3.125000;
    p = -3.6444120640178196996e-21;
    p = fma(p, w, -1.685059138182016589e-19);
    p = fma(p, w, 1.2858480715256400167e-18);
    p = fma(p, w, 1.115787767802518096e-17);
    p = fma(p, w, -1.333171662854620906e-16);
    p = fma(p, w, 2.0972767875968561637e-17);
    p = fma(p, w, 6.6376381343583238325e-15);
    p = fma(p, w, -4.0545662729752068639e-14);
    p = fma(p, w, -8.1519341976054721522e-14);
    p = fma(p, w, 2.6335093153082322977e-12);
    p = fma(p, w, -1.2975133253453532498e-11);
    p = fma(p, w, -5.4154120542946279317e-11);
    p = fma(p, w, 1.051212273321532285e-09);
    p = fma(p, w, -4.1126339803469836976e-09);
    p = fma(p, w, -2.9070369957882005086e-08);
    p = fma(p, w, 4.2347877827932403518e-07);
    p = fma(p, w, -1.3654692000834678645e-06);
    p = fma(p, w, -1.3882523362786468719e-05);
    p = fma(p, w, 0.0001867342080340571352);
    p = fma(p, w, -0.00074070253416626697512);
    p = fma(p, w, -0.0060336708714301490533);
    p = fma(p, w, 0.24015818242558961693);
    p = fma(p, w, 1.6536545626831027356);
  } else if (w < 16.000000) {
    w = std::sqrt(w) - 3.250000;
    p = 2.2137376921775787049e-09;
    p = fma(p, w, 9.0756561938885390979e-08);
    p = fma(p, w, -2.7517406297064545428e-07);
    p = fma(p, w, 1.8239629214389227755e-08);
    p = fma(p, w, 1.5027403968909827627e-06);
    p = fma(p, w, -4.013867526981545969e-06);
    p = fma(p, w, 2.9234449089955446044e-06);
    p = fma(p, w, 1.2475304481671778723e-05);
    p = fma(p, w, -4.7318229009055733981e-05);
    p = fma(p, w, 6.8284851459573175448e-05);
    p = fma(p, w, 2.4031110387097893999e-05);
    p = fma(p, w, -0.0003550375203628474796);
    p = fma(p, w, 0.00095328937973738049703);
    p = fma(p, w, -0.0016882755560235047313);
    p = fma(p, w, 0.0024914420961078508066);
    p = fma(p, w, -0.0037512085075692412107);
    p = fma(p, w, 0.005370914553590063617);
    p = fma(p, w, 1.0052589676941592334);
    p = fma(p, w, 3.0838856104922207635);
  } else {
    w = std::sqrt(w) - 5.000000;
    p = -2.7109920616438573243e-11;
    p = fma(p, w, -2.5556418169965252055e-10);
    p = fma(p, w, 1.5076572693500548083e-09);
    p = fma(p, w, -3.7894654401267369937e-09);
    p = fma(p, w, 7.6157012080783393804e-09);
    p = fma(p, w, -1.4960026627149240478e-08);
    p = fma(p, w, 2.9147953450901080826e-08);
    p = fma(p, w, -6.7711997758452339498e-08);
    p = fma(p, w, 2.2900482228026654717e-07);
    p = fma(p, w, -9.9298272942317002539e-07);
    p = fma(p, w, 4.5260625972231537039e-06);
    p = fma(p, w, -1.9681778105531670567e-05);
    p = fma(p, w, 7.5995277030017761139e-05);
    p = fma(p, w, -0.00021503011930044477347);
    p = fma(p, w, -0.00013871931833623122026);
    p = fma(p, w, 1.0103004648645343977);
    p = fma(p, w, 4.8499064014085844221);
  }
  return p * x;
}