public final void writeVarLengthUnsigned(int v) {
        int i7 = v & 0x7f;
        if ((v >>>= 7) == 0) {
            ab[aboffset++] = (byte) i7;
            return;
        }
        ab[aboffset++] = (byte) (i7 | 0x80);

        i7 = v & 0x7f;
        if ((v >>>= 7) == 0) {
            ab[aboffset++] = (byte) i7;
            return;
        }
        ab[aboffset++] = (byte) (i7 | 0x80);

        i7 = v & 0x7f;
        if ((v >>>= 7) == 0) {
            ab[aboffset++] = (byte) i7;
            return;
        }
        ab[aboffset++] = (byte) (i7 | 0x80);

        i7 = v & 0x7f;
        if ((v >>>= 7) == 0) {
            ab[aboffset++] = (byte) i7;
            return;
        }
        ab[aboffset++] = (byte) (i7 | 0x80);

        ab[aboffset++] = (byte) v;
    }
Just reserves a single byte and return it' offset.
Used in conjunction with injectVarLengthUnsigned
to efficiently write a size prefix

@return the offset of the placeholder
main/src/main/java/cgeo/geocaching/brouter/util/ByteDataWriter.java