On My Galileo
From Linux, not Arduino, if I read from A0, I get 4095 for +5V
I do this by first set the MUX for A0 to 0, the MUX is on GPIO37:
cd /sys/class/gpio
echo -n "37" >export
cd gpio37
echo -n "out" >direction
echo -n "0" >value
The reading from the ADC:
cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw
I can't check from Arduino at the moment.