[Mp4-tech] about the Initialisation process for the arithmetic decoding engine in H.264/MPEG4 standard

[zy]

hello,
I have been puzzled by a problem of the initialization process for the arithmetic decoding engine. It is said that when initilising, codIRange is set equal to 0X01FE, and codIOffset is set equal to the value returned from read_bits(9).
So, I want to know why codIRange should be set equal to 0X01FE? Can we chose 01FF? if not, why?
Preseting codIOffset means whatever 9-bit data read from stream can be the initialization value? I really want to know the answer.
Thank you.
Regard.
Yan Zheng