Optimization of java.io.DataInputStream

[Vitaly Davidovich]

Interesting - was this file codegen'd or something? Why are these nop
shifts there?

Anyway, I'd expect JIT does the right thing here and doesn't actually issue
this instruction.  Are you optimizing for interpreter or meta data size
then?

Sent from my phone
On Nov 12, 2013 3:45 AM, "Alex Yursha" <alexyursha at gmail.com> wrote:

> The following methods in java.io.DataInputStream perform right shift to
> zero positions in their implementations:
> - short readShort()
> - int readUnsignedShort()
> - char readChar()
> - int readInt()
> - long readLong()
> - String readUTF(DataInput in)
>
> For example:
>
>     public final short readShort() throws IOException {
>         int ch1 = in.read();
>         int ch2 = in.read();
>         if ((ch1 | ch2) < 0)
>             throw new EOFException();
>        return (short)((ch1 << 8) + *(ch2 << 0)*);
>     }
>
> It can be optimizied as follows:
>
>     public final short readShort() throws IOException {
>         int ch1 = in.read();
>         int ch2 = in.read();
>         if ((ch1 | ch2) < 0)
>             throw new EOFException();
>         return (short)((ch1 << 8) + *ch2*);
>     }
>
>
> This optimization saves 2 bytecode instructions in the class file code
> arrays of each method mentioned above.
>