Rewrite of IBM doublebyte charsets

Wed May 20 23:27:15 UTC 2009

5-minute review.

Looks pretty good.

Thanks for fixing old bugs found by FindXXcoderBugs.java

Thanks Ulf for your hard work on implementation and review.

Again, charset changes are very hard to review, hence scary,
but relatively easy to test in an automated fashion.

I imagine generating tests with
random input,
random charset,
random choice of direct/non-direct buffers,
and checking that charset behavior is unchanged
except for performance.

---

// it's time to generate the class file
Confusing - you're generating a source file,
and the phrase "class file" usually means
XX.class

typos:

typitcal

date structure.

correspoinding

ruondtrip

*file dbcs has trailing newlines

*Martin

On Wed, May 20, 2009 at 15:22, Xueming Shen <Xueming.Shen at sun.com> wrote:

> 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<http://cr.openjdk.java.net/%7Esherman/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<http://cr.openjdk.java.net/%7Esherman/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 UNMAPPABLE_DECODING;
>>         return b2c[b1][b2];
>>     }
>>  Benefit[1]: increase performance of decoder
>>  Benefit[2]: reduce memory of B2C_UNMAPPABLE 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 EUC_TW 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 == UNMAPPABLE_DECODING)
>>             break;
>>         da[dp++] = c;
>>         sp++;
>>     }
>>    Same for Encoder#encodeArrayLoop
>>
>> (18) Decoder_EBCDIC: boolean singlebyteState:
>>     if (singlebyteState)
>>         ...
>>
>> (19) Decoder_EBCDIC: decode single byte first:
>>     if (singlebyteState)
>>         c = b2cSB[b1];
>>     if (c == UNMAPPABLE_DECODING) {
>>         ...
>>     }
>>  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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