library(data.table)
fis.na = data.table:::fis.na
N = 1e8
set.seed(108)
N_na = 1e3
N_nan = 1e3

# integer
x = sample(N)
x[sample(N, N_na)] = NA
system.time(ans1<-is.na(x))
system.time(ans2<-fis.na(x))
identical(ans1, ans2)

# raw
x = as.raw(1:N)
system.time(ans1<-is.na(x))
system.time(ans2<-fis.na(x))
identical(ans1, ans2)

# string
x = paste0("id", 1:N)
x[sample(N, N_na)] = NA
system.time(ans1<-is.na(x))
system.time(ans2<-fis.na(x))
identical(ans1, ans2)

# double

# there is no function for "NA but not NaN"
is.na(NaN)
is.nan(NA)
is.na.only = function(x) is.na(x) & !is.nan(x)

x = runif(N)
x[sample(N, N_na)] = NA
x[sample(N, N_nan)] = NaN
system.time(ans1<-is.na(x))
system.time(ans2<-fis.na(x))
identical(ans1, ans2)

x = runif(N)
x[sample(N, N_na)] = NA
x[sample(N, N_nan)] = NaN
system.time(ans1<-is.na.only(x))
system.time(ans2<-fis.na(x, NA))
identical(ans1, ans2)

x = runif(N)
x[sample(N, N_na)] = NA
x[sample(N, N_nan)] = NaN
system.time(ans1<-is.nan(x))
system.time(ans2<-fis.na(x, NaN))
identical(ans1, ans2)