Reading 64-bit integers
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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