function bnModInverse()

in application/resources/libs/jsbn2.js [508:547]

• 40 lines of code
• 22 McCabe index (conditional complexity)

function bnModInverse(m) {
  var ac = m.isEven();
  if((this.isEven() && ac) || m.signum() == 0) return BigInteger.ZERO;
  var u = m.clone(), v = this.clone();
  var a = nbv(1), b = nbv(0), c = nbv(0), d = nbv(1);
  while(u.signum() != 0) {
    while(u.isEven()) {
      u.rShiftTo(1,u);
      if(ac) {
        if(!a.isEven() || !b.isEven()) { a.addTo(this,a); b.subTo(m,b); }
        a.rShiftTo(1,a);
      }
      else if(!b.isEven()) b.subTo(m,b);
      b.rShiftTo(1,b);
    }
    while(v.isEven()) {
      v.rShiftTo(1,v);
      if(ac) {
        if(!c.isEven() || !d.isEven()) { c.addTo(this,c); d.subTo(m,d); }
        c.rShiftTo(1,c);
      }
      else if(!d.isEven()) d.subTo(m,d);
      d.rShiftTo(1,d);
    }
    if(u.compareTo(v) >= 0) {
      u.subTo(v,u);
      if(ac) a.subTo(c,a);
      b.subTo(d,b);
    }
    else {
      v.subTo(u,v);
      if(ac) c.subTo(a,c);
      d.subTo(b,d);
    }
  }
  if(v.compareTo(BigInteger.ONE) != 0) return BigInteger.ZERO;
  if(d.compareTo(m) >= 0) return d.subtract(m);
  if(d.signum() < 0) d.addTo(m,d); else return d;
  if(d.signum() < 0) return d.add(m); else return d;
}