The function as.integer in base R will convert the hexidecimal representation of a number, e.g "0xa", into a 32-bit integer (in this case, 10). It would be good for as.integer64.character to do the same for 64-bit values.

The current implementation results in an <NA> value. An approximate work-around can be had by converting to a floating-point value, but this looses precision for large values because double contains only 53 bits of mantissa, which a signed 64-bit integer contains the equivalent of 63 bits.