How to do bitwise shifting for signed (negative) integers?

Question

In c-syntax, we can shift signed integers (negatives): We can use ">>>" if we want to force and unsigned integer shift.

y = -1732584194
(y>>16)

-26438

x = 1732584193
(x>>16)

26437

Using R, there are bitwise operators https://stat.ethz.ch/R-manual/R-devel/library/base/html/bitwise.html

?bitwShiftL for example shows the same page. It states: "Shifting is done assuming the values represent unsigned integers."

y = -1732584194
bitwShiftR(y,16)  
# [1] 39098     ## wanted -26438


x = 1732584193
bitwShiftR(x,16)
# [1] 26437    ## works as expected

Show how do I perform a signed shift using R statistical programming language?

Answer 1

You can define your own function to do this:

Rshift <- function(val, nbits) floor(val/2^nbits)

Which gives:

y = -1732584194
Rshift(y, 16)
#> [1] -26438

y = 1732584194
Rshift(y, 16)
#> [1] 26437

Or if you are used to coding in C, write a function in C and compile it as an R function using Rcpp:

Rcpp::cppFunction("long long RShift(long long a, int b) { return a >> b;}")

y = -1732584194
RShift(y, 16)
#> [1] -26438

y = 1732584194
RShift(y, 16)
#> [1] 26437