[Rd] Reading 64-bit integers
Simon Urbanek
simon.urbanek at r-project.org
Tue Mar 29 16:06:44 CEST 2011
On Mar 29, 2011, at 8:46 AM, Jon Clayden wrote:
> Dear all,
>
> I see from some previous threads that support for 64-bit integers in R
> may be an aim for future versions, but in the meantime I'm wondering
> whether it is possible to read in integers of greater than 32 bits at
> all. Judging from ?readBin, it should be possible to read 8-byte
> integers to some degree, but it is clearly limited in practice by R's
> internally 32-bit integer type:
>
>> x <- as.raw(c(0,0,0,0,1,0,0,0))
>> (readBin(x,"integer",n=1,size=8,signed=F,endian="big"))
> [1] 16777216
>> x <- as.raw(c(0,0,0,1,0,0,0,0))
>> (readBin(x,"integer",n=1,size=8,signed=F,endian="big"))
> [1] 0
>
> For values that fit into 32 bits it works fine, but for larger values
> it fails. (I'm a bit surprised by the zero - should the value not be
> NA if it is out of range?
No, it's not out of range - int is only 4 bytes so only 4 first bytes (respecting endianness order, hence LSB) are used.
> ) The value can be represented as a double,
> though:
>
>> 4294967296
> [1] 4294967296
>
> I wouldn't expect readBin() to return a double if an integer was
> requested, but is there any way to get the correct value out of it?
Trivially (for your unsigned big-endian case):
y <- readBin(x, "integer", n=length(x)/4L, endian="big")
y <- ifelse(y < 0, 2^32 + y, y)
i <- seq(1,length(y),2)
y <- y[i] * 2^32 + y[i + 1L]
Cheers,
Simon
> I
> suppose one could read the bytes into a raw vector and then
> reconstruct the number manually from that, but is there a more elegant
> or built-in solution that I'm not aware of?
>
> This is R 2.12.1 on Mac OS X.6.7 - .Machine$sizeof.long is 8.
>
> Many thanks,
> Jon
>
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