frollmax is slow on descending sequences #5923

if (!require("devtools")) install.packages("devtools")
if (!require("RCRoll")) devtools::install_github("davidcsterratt/RCRoll")
if (!require("roll")) install.packages("roll")
if (!require("data.table")) devtools::install_github("Rdatatable/data.table", branch="frollmax")

benchmark <- function(n, k, func) {
  x = func(n)
  start_time = Sys.time(); y.RCRoll = RCRoll::rollmin(x, k) ; print(paste("RCRoll:", Sys.time() - start_time))
  start_time = Sys.time(); y.roll = roll::roll_min(x, k) ; print(paste("roll:", Sys.time() - start_time))
  start_time = Sys.time(); y.data.table = data.table::frollmax(x, k) ; print(paste("data.table:", Sys.time() - start_time))
   return(list("RCRoll"=y.RCRoll, "roll"=y.roll, "data.table"=y.data.table))
}

n <- 1E7
k <- 1E3

# Random normal
out1 <- benchmark(n, k, rnorm)
# All equal to 0
out2 <- benchmark(n, k, function(n) {rep(0, n)})
# Ascending
out3 <- benchmark(n, k, function(n) {seq(0, length.out=n)})
# Descending
out4 <- benchmark(n, k, function(n) {seq(0, by=-1, length.out=n)})

[1] "RCRoll: 0.169624805450439"
[1] "roll: 0.153290987014771"
[1] "data.table: 0.0348567962646484"
[1] "RCRoll: 0.0276196002960205"
[1] "roll: 0.0650320053100586"
[1] "data.table: 0.034125804901123"
[1] "RCRoll: 0.0440917015075684"
[1] "roll: 0.0651366710662842"
[1] "data.table: 0.0270349979400635"
[1] "RCRoll: 0.0287351608276367"
[1] "roll: 0.0672793388366699"
[1] "data.table: 3.9090781211853"

> sessionInfo()
R Under development (unstable) (2023-12-29 r85751)
Platform: x86_64-pc-linux-gnu
Running under: Ubuntu 22.04.3 LTS

Matrix products: default
BLAS:   /usr/local/lib/R/lib/libRblas.so 
LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.10.0

locale:
 [1] LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_GB.UTF-8        LC_COLLATE=en_GB.UTF-8    
 [5] LC_MONETARY=en_GB.UTF-8    LC_MESSAGES=en_GB.UTF-8   
 [7] LC_PAPER=en_GB.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_GB.UTF-8 LC_IDENTIFICATION=C       

time zone: Europe/London
tzcode source: system (glibc)

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] data.table_1.14.99 RcppRoll_0.3.0     zoo_1.8-12         roll_1.1.6        
[5] RCRoll_0.1         devtools_2.4.5     usethis_2.2.2     

loaded via a namespace (and not attached):
 [1] miniUI_0.1.1.1     compiler_4.4.0     promises_1.2.1     Rcpp_1.0.12       
 [5] stringr_1.5.1      later_1.3.2        fastmap_1.1.1      lattice_0.20-45   
 [9] mime_0.12          R6_2.5.1           htmlwidgets_1.6.4  profvis_0.3.8     
[13] shiny_1.8.0        rlang_1.1.3        cachem_1.0.8       stringi_1.8.3     
[17] httpuv_1.6.13      fs_1.6.3           RcppParallel_5.1.7 pkgload_1.3.3     
[21] memoise_2.0.1      cli_3.6.2          magrittr_2.0.3     grid_4.4.0        
[25] digest_0.6.34      xtable_1.8-4       remotes_2.4.2.1    lifecycle_1.0.4   
[29] vctrs_0.6.5        glue_1.7.0         urlchecker_1.0.1   sessioninfo_1.2.2 
[33] pkgbuild_1.4.3     purrr_1.0.2        tools_4.4.0        ellipsis_0.3.2    
[37] htmltools_0.5.7