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1 \name{packing}
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2 \alias{.pack}
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3 \alias{packing}
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4 \alias{.unpack}
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5 \title{Handling of foreign C fundamental data types}
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6 \description{Functions to unpack/pack (read/write) foreign C data types from/to R atomic vectors and C data objects such as arrays and pointers to structures.}
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7 \usage{
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8 .pack(x, offset, sigchar, value)
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9 .unpack(x, offset, sigchar)
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10 }
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11 \arguments{
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12 \item{x}{atomic vector (logical, raw, integer or double) or external pointer.}
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13 \item{offset}{integer specifying \emph{byte offset} starting at 0.}
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14 \item{sigchar}{character string specifying the C data type by a \link{type signature}.}
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15 \item{value}{R object value to be coerced and packed to a foreign C data type.}
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16 }
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17 \details{
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18 The function \code{.pack} converts an R \code{value} into a C data type specified by the \link{signature} \code{sigchar}
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19 and it writes the raw C foreign data value at byte position \code{offset} into the object \code{x}.
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20 The function \code{.unpack} extracts a C data type according to the \link{signature} \code{sigchar}
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21 at byte position \code{offset} from the object \code{x} and converts the C value to an R value and returns it.
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22
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23 Byte \code{offset} calculations start at 0 relative to the first byte in an atomic vectors data area.
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24
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25 If \code{x} is an atomic vector, a bound check is carried out before read/write access.
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26 Otherwise, if \code{x} is an external pointer, there is only a C NULL pointer check.
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27 }
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28 \value{
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29 \code{.unpack} returns a read C data type coerced to an R value.
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30 }
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31 \seealso{
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32 \code{\link{.dyncall}} for details on type signatures.
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33 }
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34 \examples{
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35 # transfer double to array of floats and back, compare precision:
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36 n <- 6
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37 input <- rnorm(n)
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38 buf <- raw(n*4)
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39 for (i in 1:n) {
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40 .pack(buf, 4*(i-1), "f", input[i])
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41 }
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42 output <- numeric(n)
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43 for (i in 1:n) {
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44 output[i] <- .unpack(buf, 4*(i-1), "f")
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45 }
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46 # difference between double and float
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47 difference <- output-input
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48 print( cbind(input,output,difference) )
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49 }
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