ParagonIE_Sodium_Core_Curve25519::ge_scalarmult_base

    public static function ge_scalarmult_base($a)
    {
        /** @var array<int, int> $e */
        $e = array();
        $r = new ParagonIE_Sodium_Core_Curve25519_Ge_P1p1();

        for ($i = 0; $i < 32; ++$i) {
            /** @var int $dbl */
            $dbl = (int) $i << 1;
            $e[$dbl] = (int) self::chrToInt($a[$i]) & 15;
            $e[$dbl + 1] = (int) (self::chrToInt($a[$i]) >> 4) & 15;
        }

        /** @var int $carry */
        $carry = 0;
        for ($i = 0; $i < 63; ++$i) {
            $e[$i] += $carry;
            /** @var int $carry */
            $carry = $e[$i] + 8;
            /** @var int $carry */
            $carry >>= 4;
            $e[$i] -= $carry << 4;
        }
        /** @var array<int, int> $e */
        $e[63] += (int) $carry;

        $h = self::ge_p3_0();

        for ($i = 1; $i < 64; $i += 2) {
            $t = self::ge_select((int) floor($i / 2), (int) $e[$i]);
            $r = self::ge_madd($r, $h, $t);
            $h = self::ge_p1p1_to_p3($r);
        }

        $r = self::ge_p3_dbl($h);

        $s = self::ge_p1p1_to_p2($r);
        $r = self::ge_p2_dbl($s);
        $s = self::ge_p1p1_to_p2($r);
        $r = self::ge_p2_dbl($s);
        $s = self::ge_p1p1_to_p2($r);
        $r = self::ge_p2_dbl($s);

        $h = self::ge_p1p1_to_p3($r);

        for ($i = 0; $i < 64; $i += 2) {
            $t = self::ge_select($i >> 1, (int) $e[$i]);
            $r = self::ge_madd($r, $h, $t);
            $h = self::ge_p1p1_to_p3($r);
        }
        return $h;
    }