Use (1 << 31) as the multiplier for int<->float conversions. This makes sure that int->float conversions always end up with floats between [-1.0, 1.0]. For the conversion from float to int, this multiplier will give the complete int range after we perform clipping. Change the unit test to take this into consideration. Fixes https://bugzilla.gnome.org/show_bug.cgi?id=755301