Re: ClassReader.readUtf and compact strings

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Thanks for your experiments! The String constructor using a Charset is 
only available in JDK 1.6, and we maintain 1.5 compatibility currently, 
so we can't use it.

Le 06/02/2021 à 11:42, Eirik Bjørsnøs (via asm Mailing List) a écrit :
>     I imagine there could be a performance win of not doing this byte[]
>     -> char[] -> byte[] dance, given that most class strings are ASCII
>     anyway.
> 
> 
> I did a quick implementation of this and could not observe any 
> performance difference. Probably the JIT optimizes much of this away, or 
> the cost of array copying is dominating.
> 
> The change did remove some crufty code though, which might be a win, if 
> only in terms of readability / maintainability.
> 
> Cheers,
> Eirik.
> 
> 
> class FastClassReader extends ClassReader {
> 
>      public FastClassReader(byte[] classfileBuffer) {
>          super(classfileBuffer);
>      }
> 
>      @Override
>      public final String readUTF8(int offset, char[] charBuffer) {
>          int constantPoolEntryIndex = readUnsignedShort(offset);
>          if (offset == 0 || constantPoolEntryIndex == 0) {
>              return null;
>          }
>          return fastReadUtf(constantPoolEntryIndex);
>      }
> 
>      private String fastReadUtf(final int constantPoolEntryIndex) {
>          String value = constantUtf8Values[constantPoolEntryIndex];
>          if (value != null) {
>              return value;
>          }
>          return fastReadString(constantPoolEntryIndex);
>      }
> 
>      private String fastReadString(int constantPoolEntryIndex) {
>          int cpInfoOffset = getItem(constantPoolEntryIndex);
>          return constantUtf8Values[constantPoolEntryIndex] =
>                  new String(classFileBuffer, cpInfoOffset + 2, 
> readUnsignedShort(cpInfoOffset), StandardCharsets.UTF_8);
>      }
> 
> }
> 
> 
> 

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