RFR: JDK-8074579 Use more efficient and readable way of checking PKZIP signatures

[Martin Buchholz]

I actually benchmarked my last suggestion to be 20% faster on an ad-hoc
microbenchmark.  We can go faster yet on x86 if we use unaligned 4-byte
uint32 reads.  Maybe in a future change.

In general, hardware is moving in the direction of allowing unaligned reads
without performance penalty, especially on x86, and it would be good to
start taking advantage of that.

On Fri, Mar 6, 2015 at 9:50 PM, Martin Buchholz <martinrb at google.com> wrote:

> Err...
>
> #define PKZIP_SIGNATURE_AT(p, b2, b3) \
>   (((p)[0] == 'P') & ((p)[1] == 'K') & ((p)[2] == b2) & ((p)[3] == b3))
>
>