Rewrite of IBM doublebyte charsets (original) (raw)

Xueming Shen Xueming.Shen at Sun.COM
Thu May 14 22:03:18 UTC 2009

Ulf Zibis wrote:

Am 12.05.2009 20:31, Xueming Shen schrieb:

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. But I wonder, that you don't consider my XOR approach. The XOR needs only to be computed once in contrast to 3 times computing AND + comparing against -1 (needs load operation in contrast to compare '< 0') What is the "XOR approach"? I might have miss it. I'm happy to try it out. OK, the "3 times computing" and "compare <0" are the good hint to improve, the latest one looks like

180 int cnsPlane = sa[sp +1]; 181 if ((cnsPlane & 0xf0) != 0xa0 || 182 (cnsPlane = cnspToIndex[cnsPlane&0x0f]) < 0) 183 return CoderResult.malformedForLength(2);

And it definitely is better than the previous one, thanks! :-) Now maybe you might want to eye the IBM db webrev, any change would benefit several charsets:-)

Sherman

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