Rewrite of IBM doublebyte charsets

[Xueming Shen]

Ulf Zibis wrote:
> Sherman,
> thanks for verifying my suggestions.
>
> > (1) simplify the "plane number" byte check by adding a new static 
> array of cnspToIndex[16] for decoder
>
> or simply:
>
>       static final byte[] cnspToIndex = new byte[0x100];
>       static {
>           Arrays.fill(cnspToIndex, -1);
>           cnspToIndex[0xa2] = 1; cnspToIndex[0xa3] = 2; 
> cnspToIndex[0xa4] = 3;
>           cnspToIndex[0xa5] = 4; cnspToIndex[0xa6] = 5; 
> cnspToIndex[0xa7] = 6; cnspToIndex[0xaf] = 7;
>       }
>
>            if ((cnsPlane = cnspToIndex[sa[sp + 1] && 0xff]) < 0)
>                return CoderResult.malformedForLength(2);
>
considered that, but ended up thinking it might not really worth the 
0x100 bytes:-) at least based on my measurement.

>
> *** Question: Why you code:
>
>                   } else if ((byte1 & MSB) == 0) {  // ASCII  G0
>
> instead of:
>
>                   } else if (byte1 >= 0) {  // ASCII  G0
>
I believe this line was written 10 years ago, so I have no idea (or 
forgot) why we picked this one, my guess is the code might
be a little easier to read with "MSB"...you think the >=0 is better or 
faster/




> ???
>
> -Ulf
>
>