invmodp: function()

in src/ff.js [604:673]
60 lines of code
11 McCabe index (conditional complexity)

        invmodp: function(p) {
            var n = p.length,
                u = new FF(n),
                v = new FF(n),
                x1 = new FF(n),
                x2 = new FF(n),
                t = new FF(n),
                one = new FF(n);

            one.one();
            u.copy(this);
            v.copy(p);
            x1.copy(one);
            x2.zero();

            // reduce n in here as well!
            while (FF.comp(u, one) !== 0 && FF.comp(v, one) !== 0) {
                while (u.parity() === 0) {
                    u.shr();
                    if (x1.parity() !== 0) {
                        x1.add(p);
                        x1.norm();
                    }
                    x1.shr();
                }

                while (v.parity() === 0) {
                    v.shr();
                    if (x2.parity() !== 0) {
                        x2.add(p);
                        x2.norm();
                    }
                    x2.shr();
                }

                if (FF.comp(u, v) >= 0) {
                    u.sub(v);
                    u.norm();

                    if (FF.comp(x1, x2) >= 0) {
                        x1.sub(x2);
                    } else {
                        t.copy(p);
                        t.sub(x2);
                        x1.add(t);
                    }

                    x1.norm();
                } else {
                    v.sub(u);
                    v.norm();

                    if (FF.comp(x2, x1) >= 0) {
                        x2.sub(x1);
                    } else {
                        t.copy(p);
                        t.sub(x1);
                        x2.add(t);
                    }

                    x2.norm();
                }
            }

            if (FF.comp(u, one) === 0) {
                this.copy(x1);
            } else {
                this.copy(x2);
            }
        },