Unsafe.{get,put}-X-Unaligned; Efficient array comparison intrinsics (original) (raw)

Andrew Haley aph at redhat.com
Wed Mar 4 15:21:08 UTC 2015

On 03/04/2015 02:29 PM, Andrew Haley wrote:

My inclination is to remove the get*Unaligned(..., boolean bigEndian) methods and thereby consistently use Bits.swap in the heap buffer. A similar pattern applies for float/double conversion. I suggest that you and John argue that between yourselves! I think there's a lot to be said for that approach on architectures which can do unaligned accesses and have big- and little-endian memory operators.

The new API gives us HeapByteBuffer methods

public long getLong(int i) {
    return unsafe.getLongUnaligned(hb, byteOffset(checkIndex(i, 8)), bigEndian);
}

If we get rid of the get*Unaligned(..., boolean bigEndian) methods we'll end up with

public long getLong(int i) {
    long x = unsafe.getLongUnaligned(hb, byteOffset(checkIndex(i, 8)));
    return nativeByteOrder ? x : Bits.swap(x));
}

... which has the disadvantage that all of the Buffer methods have to know about the native endianness.

One suggestion: if we exposed Unsafe.fromEndian we could do something like

public long getLong(int i) {
    long x = unsafe.getLongUnaligned(hb, byteOffset(checkIndex(i, 8)));
    return unsafe.fromEndian(bigEndian, x));
}

Andrew.

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