RFR: JDK-8189611: JarFile versioned stream and real name support

[Martin Buchholz]

(How hard is it to rename that hotspot intrinsic to isAscii?)

On Wed, Nov 29, 2017 at 4:03 PM, Martin Buchholz <martinrb at google.com>
wrote:

> +    private static boolean isASCII(byte[] ba, int off, int len) {+        for (int i = off; i < off + len; i++) {+            if (ba[i] < 0)+                return false;+        }+        return true;+    }
>
> I see that StringCoding has
>
>     @HotSpotIntrinsicCandidate
>     public static boolean hasNegatives(byte[] ba, int off, int len) {
>         for (int i = off; i < off + len; i++) {
>             if (ba[i] < 0) {
>                 return true;
>             }
>         }
>         return false;
>     }
>
> and in hotspot-land I see that MacroAssembler::has_negatives has 200 lines
> of hairy assemblerese.  Let's reuse that enormous effort!  And not just in
> ZipCoder.java - needing to check a byte sequence for Ascii-ness is a bit
> goofy but important enough to be a public API  (I've used optimized
> versions of this in other languages).  I don't know where it belongs (could
> add a method to CharsetDecoder, intrinsified for US_ASCII), but we can find
> one.  Even without that, surely today we should be able to reuse this
> intrinsic from somewhere else within the java.base module.
>
> (Keeping high-performance intrinsics hidden is a top reason why java
> developers use jdk internals)
>
> (Not directed at Xueming in particular)
>