Can access by local method variables be faster then access by member variables ?

[Xiaobin Lu]

I suspect that adding two members to the object would increase the 
object size which might affect the efficiency of object allocation. Have 
you had a chance to look at the generated code, it might be possible 
that the method itself is inlined so the pop/push operations have been 
completely eliminated?

-Xiaobin

Ulf Zibis wrote:
> Hi experts,
>
> to avoid stack push + pop of src, dst I have refactored my code in 
> moving the local method variables (sp, ...) to member variables 
> (srcPos, ...).
>
> After this I have experienced that my code was little slower.
>
> For full source code see:
> https://java-nio-charset-enhanced.dev.java.net/source/browse/java-nio-charset-enhanced/trunk/src/sun/nio/cs/SingleByteEncoder.java?rev=291&view=markup 
>
> https://java-nio-charset-enhanced.dev.java.net/source/browse/java-nio-charset-enhanced/trunk/src/sun/nio/cs/SingleByteEncoder.java?rev=302&view=markup 
>
>
> ======================================== revisions 291 
> ========================================
>
>    private CoderResult encodeArraysLoop(CharBuffer src, ByteBuffer dst) {
>        char[] sa = src.array();
>        int sp = src.arrayOffset() + src.position();
>        int sl = src.arrayOffset() + src.limit();
>        assert (sp <= sl);
>        byte[] da = dst.array();
>        int dp = dst.arrayOffset() + dst.position();
>        int dl = dst.arrayOffset() + dst.limit();
>        assert (dp <= dl);
>        try {
>            for (; sp < sl; sp++) {
>                current = sa[sp];
>                byte b = encodeSingle();
>                if (dp >= dl)
>                    return CoderResult.OVERFLOW;
>                da[dp++] = b;
>            }
>            return CoderResult.UNDERFLOW;
>        } catch (UnmappableCharacterException e) {
>            if (Surrogate.isLow(current) || current >= '\uFFFE')
>                return CODERRESULT_MALFORMED;
>            if (Surrogate.isHigh(current))
>                try {
>                    if (sp+1 >= sl)
>                        return CoderResult.UNDERFLOW;
>                    encodeSurrogate(sa[sp+1]);
>                } catch (UnmappableCharacterException e2) {
>                    return CODERRESULT_UNMAPPABLE2;
>                } catch (MalformedInputException e2) {
>                    return CODERRESULT_MALFORMED2;
>                }
>            return CODERRESULT_UNMAPPABLE;
>        } finally {
>            src.position(sp - src.arrayOffset());
>            dst.position(dp - dst.arrayOffset());
>        }
>    }
>
> ======================================== revisions 302 
> ========================================
>
>    private CoderResult encodeArraysLoop() throws RuntimeException, 
> UnmappableCharacterException {
>        for (; srcPos < srcLimit; srcPos++) {
>            current = srcArray[srcPos];
>            byte b = encodeSingle();
>            if (dstPos < dstLimit)
>                dstArray[dstPos++] = b;
>            else
>                return CoderResult.OVERFLOW;
>        }
>        return CoderResult.UNDERFLOW;
>    }
>
> =============================================================================================== 
>
>
>
> Thanks for your explanations,
>
> Ulf
>
>
>
>