Rewrite of IBM doublebyte charsets (original) (raw)

Xueming Shen Xueming.Shen at Sun.COM
Wed May 20 22:22:04 UTC 2009

Ulf, thanks for the review!

Now we have a bugid for this one. The webrev has been updated to address some of your suggestions (see my below) and rename to

http://cr.openjdk.java.net/~sherman/6843578/webrev (old webrevs are still there with webrev.0x)

With this change, (1)21% reduce of rt.jar size (from 2.99M-with the euc_tw reduce to 2.35M) (2)much faster coding performance, a quick/not_really_a_benchmark result can been found at http://cr.openjdk.java.net/~sherman/6843578/codingPerm (3)also addressed the bugids listed below.

6639450: IBM949C encoder modifies state of IBM949 encoder 6569191: Cp943 io converter returns U+0000 and U+FFFD for unconvertable character 6577466: Character encoder IBM970 throws a BufferOverflowException 5065777: CharsetEncoder canEncode() methods often incorrectly return false

The test case test/sun/nio/cs/OLD/TestIBMDB.java is used to make sure there is no mapping regression, there are new mapping entries added (because switching to the latest IBM cdc mapping tables for some charsets, which the b2c tables we have are not accurate/complete), but no conflit with previous mappings.

Alan, Martin, I need you guys also help review the change, I will need a name on the putback message. The number of file is huge, but only the files listed at beginning need attention:-)

Sherman

Ulf Zibis wrote:

*** Decoder-Suggestions: (1) Unused imports in DoubleByte-X.java: import java.util.Arrays; import sun.nio.cs.StandardCharsets; import static sun.nio.cs.CharsetMapping.*; import sun.nio.cs.ext.DoubleByte; // or instead: static sun.nio.cs.ext.DoubleByte.*; done! good catch.

(3) Modify dimension of b2c: char[][] b2c = new char[0x100][segSize]; so decode : public char decodeDouble(int b1, int b2) { if ((b2-=b2Min) < 0 || b2 >= segSize) return UNMAPPABLEDECODING; return b2c[b1][b2]; } Benefit[1]: increase performance of decoder Benefit[2]: reduce memory of B2CUNMAPPABLE from 8192 to 512 bytes Benefit[3]: some of b2c pages could be saved (if only containing \uFFFD) A good suggestion. I tried, and it does bring in about 10%+% gain of decoding (for non-direct buffer, we also have similar gian in direct buffer, but the % number is not this big). The webrev has been updated for this one.

(4) Don't care about b2Max (it's always not far from 0xff): Benefit[4]: another performance increase of decoder (only check: (b2-=b2Min) < 0) Decided to keep it. We do have some charsets (not included this time) that care about b2max.

(5) Truncate String segments (there are 65 % "\uFFFD" in IBM933): (fill b2c segments first with "\uFFFD", then initialize) Benefit[5]: save up to 180 % superfluous memory and disk-footprint Changing from the b2c index from 4-bit to 8-bit (#2) should have already improved this a lot (I see a 1.5%+ improvement of overall charsets.jar)

(6) Unload b2cStr from memory after startup: - outsource b2cStr to additional class file like EUCTW approach - set b2cStr = null after startup (remove final modifier) Benefit[6]: avoid 100 % superfluous memory-footprint I doubt it really saves something real, since the "class" should still keep its copy somewhere...and I will need it for c2b (now I'm "delaying" the c2b init)

(7) Avoid copying b2cStr to b2c: (String#charAt() is fast as char[] access) Benefit[7]: increase startup performance for decoder I tried again last night. char[][] is much faster than the String[] version in both client and server vm. So keep it asis. (this was actually I switched from String[] to char[][])

(9) Share mappings (IBM930 and IBM939 are 99 % identical): Benefit[9]: save up to 99 % superfluous disk-footprint Benefit[10]: save up to 99 % superfluous memory-footprint (if both charsets are loaded) I still want to keep one map for one charset, at least for now. It might be something worth researching in the future.

(12) Get rid of sun.io package dependency:

https://java-nio-charset-enhanced.dev.java.net/source/browse/java-nio-charset-enhanced/tags/milestone2/src/sun/io/ Benefit[13]: avoid superfluous disk-footprint Benefit[14]: save maintenance of sun.io converters Disadvantage[1]: published under JRL (waiting for launch of OpenJDK-7 project "charset-enhancement") ;-) This is not something about engineering. It's about license, policy...

(17) Decoder#decodeArrayLoop: shortcut for single byte only: int sr = src.remaining(); int sl = sp + sr; int dr = dst.remaining(); int dl = dp + dr; // single byte only loop int slSB = sp + sr < dr ? sr : dr; while (sp < slSB) { char c = b2cSB[sa[sp] && 0xff]; if (c == UNMAPPABLEDECODING) break; da[dp++] = c; sp++; } Same for Encoder#encodeArrayLoop (18) DecoderEBCDIC: boolean singlebyteState: if (singlebyteState) ... (19) DecoderEBCDIC: decode single byte first: if (singlebyteState) c = b2cSB[b1]; if (c == UNMAPPABLEDECODING) { ... } Benefit[20]: should be faster Not like when we dealing with singlebyte charsets. For doublebyte charsets the priority should be given to doublebyte codepoints, if possible. Not single byte codepoints.

*** Encoder-Suggestions:

(21) join *.nr to *.c2b files (25->000a becomes 000a->fffd): Benefit[21]: reduce no. of files Benefit[22]: simplifies initC2B() (avoids 2 loops) In theory you can do some magic to "join" .nr into .c2b. The price might be more complicated logic depends on the codepoints. You may end up doing some table lookup for each codepoint in b2c when processing.

And big thanks for all the suggestions.

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