ParagonIE_Sodium_Core_Curve25519::ge_frombytes_negate_vartime

    public static function ge_frombytes_negate_vartime($s)
    {
        static $d = null;
        if (!$d) {
            $d = ParagonIE_Sodium_Core_Curve25519_Fe::fromArray(self::$d);
        }

        # fe_frombytes(h->Y,s);
        # fe_1(h->Z);
        $h = new ParagonIE_Sodium_Core_Curve25519_Ge_P3(
            self::fe_0(),
            self::fe_frombytes($s),
            self::fe_1()
        );

        # fe_sq(u,h->Y);
        # fe_mul(v,u,d);
        # fe_sub(u,u,h->Z);       /* u = y^2-1 */
        # fe_add(v,v,h->Z);       /* v = dy^2+1 */
        $u = self::fe_sq($h->Y);
        /** @var ParagonIE_Sodium_Core_Curve25519_Fe $d */
        $v = self::fe_mul($u, $d);
        $u = self::fe_sub($u, $h->Z); /* u =  y^2 - 1 */
        $v = self::fe_add($v, $h->Z); /* v = dy^2 + 1 */

        # fe_sq(v3,v);
        # fe_mul(v3,v3,v);        /* v3 = v^3 */
        # fe_sq(h->X,v3);
        # fe_mul(h->X,h->X,v);
        # fe_mul(h->X,h->X,u);    /* x = uv^7 */
        $v3 = self::fe_sq($v);
        $v3 = self::fe_mul($v3, $v); /* v3 = v^3 */
        $h->X = self::fe_sq($v3);
        $h->X = self::fe_mul($h->X, $v);
        $h->X = self::fe_mul($h->X, $u); /* x = uv^7 */

        # fe_pow22523(h->X,h->X); /* x = (uv^7)^((q-5)/8) */
        # fe_mul(h->X,h->X,v3);
        # fe_mul(h->X,h->X,u);    /* x = uv^3(uv^7)^((q-5)/8) */
        $h->X = self::fe_pow22523($h->X); /* x = (uv^7)^((q-5)/8) */
        $h->X = self::fe_mul($h->X, $v3);
        $h->X = self::fe_mul($h->X, $u); /* x = uv^3(uv^7)^((q-5)/8) */

        # fe_sq(vxx,h->X);
        # fe_mul(vxx,vxx,v);
        # fe_sub(check,vxx,u);    /* vx^2-u */
        $vxx = self::fe_sq($h->X);
        $vxx = self::fe_mul($vxx, $v);
        $check = self::fe_sub($vxx, $u); /* vx^2 - u */

        # if (fe_isnonzero(check)) {
        #     fe_add(check,vxx,u);  /* vx^2+u */
        #     if (fe_isnonzero(check)) {
        #         return -1;
        #     }
        #     fe_mul(h->X,h->X,sqrtm1);
        # }
        if (self::fe_isnonzero($check)) {
            $check = self::fe_add($vxx, $u); /* vx^2 + u */
            if (self::fe_isnonzero($check)) {
                throw new RangeException('Internal check failed.');
            }
            $h->X = self::fe_mul(
                $h->X,
                ParagonIE_Sodium_Core_Curve25519_Fe::fromArray(self::$sqrtm1)
            );
        }

        # if (fe_isnegative(h->X) == (s[31] >> 7)) {
        #     fe_neg(h->X,h->X);
        # }
        $i = self::chrToInt($s[31]);
        if (self::fe_isnegative($h->X) === ($i >> 7)) {
            $h->X = self::fe_neg($h->X);
        }

        # fe_mul(h->T,h->X,h->Y);
        $h->T = self::fe_mul($h->X, $h->Y);
        return $h;
    }