public double getDouble(final int index) {
        this.checkIndexLength(index, SIZE_OF_DOUBLE);
        return Holder.unsafe.getDouble(this.base, this.address + index);
    }
Gets a 64-bit double at the specified absolute {@code index} in
this buffer.

@throws IndexOutOfBoundsException if the specified {@code index} is less than {@code 0} or
{@code index + 8} is greater than {@code this.length()}
embulk-core/src/main/java/org/embulk/exec/Slice.java