ParagonIE_Sodium_Core_Curve25519::ge_select

    public static function ge_select($pos = 0, $b = 0)
    {
        static $base = null;
        if ($base === null) {
            $base = array();
            /** @var int $i */
            foreach (self::$base as $i => $bas) {
                for ($j = 0; $j < 8; ++$j) {
                    $base[$i][$j] = new ParagonIE_Sodium_Core_Curve25519_Ge_Precomp(
                        ParagonIE_Sodium_Core_Curve25519_Fe::fromArray($bas[$j][0]),
                        ParagonIE_Sodium_Core_Curve25519_Fe::fromArray($bas[$j][1]),
                        ParagonIE_Sodium_Core_Curve25519_Fe::fromArray($bas[$j][2])
                    );
                }
            }
        }
        /** @var array<int, array<int, ParagonIE_Sodium_Core_Curve25519_Ge_Precomp>> $base */
        if (!is_int($pos)) {
            throw new InvalidArgumentException('Position must be an integer');
        }
        if ($pos < 0 || $pos > 31) {
            throw new RangeException('Position is out of range [0, 31]');
        }

        /** @var int $bnegative */
        $bnegative = self::negative($b);
        /** @var int $babs */
        $babs = $b - (((-$bnegative) & $b) << 1);

        $t = self::ge_precomp_0();
        for ($i = 0; $i < 8; ++$i) {
            $t = self::cmov(
                $t,
                $base[$pos][$i],
                self::equal($babs, $i + 1)
            );
        }
        $minusT = new ParagonIE_Sodium_Core_Curve25519_Ge_Precomp(
            self::fe_copy($t->yminusx),
            self::fe_copy($t->yplusx),
            self::fe_neg($t->xy2d)
        );
        return self::cmov($t, $minusT, $bnegative);
    }