R devel - Mar 2011 - Reading 64-bit integers

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?) 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? 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

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
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
> 
>

> -----Original Message-----
> From: r-devel-bounces at r-project.org 
> [mailto:r-devel-bounces at r-project.org] On Behalf Of Jon Clayden
> Sent: Tuesday, March 29, 2011 5:46 AM
> To: r-devel at r-project.org
> Subject: [Rd] Reading 64-bit integers
> 
> 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?) 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?
In S+'s readBin() you can use the argument output="double" to
read 8-byte integers from a file and to put the closest equivalent
value into a double precision vector.  It is also useful when reading
unsigned 4-byte integers that may be above 2^31.  The help file says
   output
          Like what but used when the type of data in the file is
          different than the type of S-PLUS vector used to store the
          data. what refers to the data in the file and output refers to
          the output of readBin. output=double() is useful for reading
          unsigned 4 byte integers (so integers bigger than 2^31 are not
          read as negative numbers) or even for 8 byte integers on
32-bit
          versions of Splus. In the latter case you may lose some
          precision, but reading it as 4 byte integers will omit the 4
          high order bytes.
 
> 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
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>