A DESCRIPTION OF THE REQUEST :
Current xBufferLoop checks the bounds of the buffers by querying Buffer by its remaining() method.
After, the bounds are checked 2nd time internally by Buffer's get()/put() methods.


JUSTIFICATION :
If the first of this redundunt checks would be saved, xBufferLoop would become faster.
See my example from UTF_8$Encoder below ...


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
        private CoderResult encodeBufferLoop(CharBuffer src, ByteBuffer dst) {

            int mark = src.position(); // TODO: maybe instead use src.mark(); evaluate by microbenchmark!
            while (true) try {
                dst.mark();
                int c = src.get();
                if (c < 0x80) {
                    // Have at most seven bits
                    dst.put((byte)c);
                } else if (c < 0x800) {
                    // 2 bytes, 11 bits
                    dst.put((byte)(0xc0 | ((c >> 06))));
                    dst.put((byte)(0x80 | (c & 0x3f)));
                } else if (Surrogate.is(c)) {
                    // Have a surrogate pair
                    if (sgp == null)
                        sgp = new Surrogate.Parser();
                    int uc = sgp.parse((char)c, src); // TODO: throw exception there, if src is empty
                    if (uc < 0) {
                        src.position(mark);
                        return sgp.error();
                    }
                    dst.put((byte)(0xf0 | ((uc >> 18))));
                    dst.put((byte)(0x80 | ((uc >> 12) & 0x3f)));
                    dst.put((byte)(0x80 | ((uc >> 06) & 0x3f)));
                    dst.put((byte)(0x80 | (uc & 0x3f)));
                    mark++; //2 chars
                } else {
                    // 3 bytes, 16 bits
                    dst.put((byte)(0xe0 | ((c >> 12))));
                    dst.put((byte)(0x80 | ((c >> 06) & 0x3f)));
                    dst.put((byte)(0x80 | (c & 0x3f)));
                }
                mark++;
            } catch (BufferUnderflowException bue) {
                return underflow(src, mark);
            } catch (BufferOverflowException boe) {
                dst.reset();
                return overflow(src, mark);
            }
        }

ACTUAL -
        private CoderResult encodeBufferLoop(CharBuffer src, ByteBuffer dst) {

            int mark = src.position();
            while (src.hasRemaining()) {
                int c = src.get();
                if (c < 0x80) {
                    // Have at most seven bits
                    if (!dst.hasRemaining())
                        return overflow(src, mark);
                    dst.put((byte)c);
                } else if (c < 0x800) {
                    // 2 bytes, 11 bits
                    if (dst.remaining() < 2)
                        return overflow(src, mark);
                    dst.put((byte)(0xc0 | ((c >> 06))));
                    dst.put((byte)(0x80 | (c & 0x3f)));
                } else if (Surrogate.is(c)) {
                    // Have a surrogate pair
                    if (sgp == null)
                        sgp = new Surrogate.Parser();
                    int uc = sgp.parse((char)c, src);
                    if (uc < 0) {
                        src.position(mark);
                        return sgp.error();
                    }
                    if (dst.remaining() < 4)
                        return overflow(src, mark);
                    dst.put((byte)(0xf0 | ((uc >> 18))));
                    dst.put((byte)(0x80 | ((uc >> 12) & 0x3f)));
                    dst.put((byte)(0x80 | ((uc >> 06) & 0x3f)));
                    dst.put((byte)(0x80 | (uc & 0x3f)));
                    mark++; //2 chars
                } else {
                    // 3 bytes, 16 bits
                    if (dst.remaining() < 3)
                        return overflow(src, mark);
                    dst.put((byte)(0xe0 | ((c >> 12))));
                    dst.put((byte)(0x80 | ((c >> 06) & 0x3f)));
                    dst.put((byte)(0x80 | (c & 0x3f)));
                }
                mark++;
            }
            src.position(mark);
            return CoderResult.UNDERFLOW;
        }