From 4370a7903b4d1041ac4c95e3ea60353f7bc75535 Mon Sep 17 00:00:00 2001
From: Andrew Johnson <andrew.johnson@arjohnsonau.com>
Date: Tue, 7 Oct 2025 18:11:02 +0800
Subject: [PATCH 1/2] Remove unnecessary flag for WINARM64

---
 R/tbb.R                     | 8 --------
 inst/include/RcppParallel.h | 3 ---
 2 files changed, 11 deletions(-)

diff --git a/R/tbb.R b/R/tbb.R
index ac1050f3..f9ca5cb5 100644
--- a/R/tbb.R
+++ b/R/tbb.R
@@ -58,14 +58,6 @@ tbbCxxFlags <- function() {
       return("-DRCPP_PARALLEL_USE_TBB=0")
    
    flags <- c("-DRCPP_PARALLEL_USE_TBB=1")
-   
-   # TBB does not have assembly code for Windows ARM64
-   # so we need to use compiler builtins
-   if (TBB_ENABLED && is_windows()) {
-      if (R.version$arch == "aarch64") {
-         flags <- c(flags, "-DTBB_USE_GCC_BUILTINS")
-      }
-   }
 
    # if TBB_INC is set, apply those library paths
    tbbInc <- Sys.getenv("TBB_INC", unset = TBB_INC)
diff --git a/inst/include/RcppParallel.h b/inst/include/RcppParallel.h
index c7fdf0bc..87d6eb5c 100644
--- a/inst/include/RcppParallel.h
+++ b/inst/include/RcppParallel.h
@@ -18,9 +18,6 @@
 #endif
 
 #if RCPP_PARALLEL_USE_TBB
-# if defined(WINNT) && defined(__aarch64__) && !defined(TBB_USE_GCC_BUILTINS)
-#  define TBB_USE_GCC_BUILTINS 1
-# endif
 # include "RcppParallel/TBB.h"
 #endif
 

From 811e8848d04c4e6add5a277ea630fa8971129e80 Mon Sep 17 00:00:00 2001
From: Andrew Johnson <andrew.johnson@arjohnsonau.com>
Date: Wed, 8 Oct 2025 00:06:59 +0800
Subject: [PATCH 2/2] Fix TBB library lookup

---
 R/tbb.R | 2 +-
 R/zzz.R | 5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/R/tbb.R b/R/tbb.R
index f9ca5cb5..3d8fbb32 100644
--- a/R/tbb.R
+++ b/R/tbb.R
@@ -24,7 +24,7 @@ tbbLibraryPath <- function(name = NULL) {
    # form library names
    tbbLibNames <- list(
       "Darwin"  = paste0("lib", name, ".dylib"),
-      "Windows" = paste0(       name, ".dll"),
+      "Windows" = paste0("lib", name, c("12", ""), ".a"),
       "SunOS"   = paste0("lib", name, ".so"),
       "Linux"   = paste0("lib", name, c(".so.2", ".so"))
    )
diff --git a/R/zzz.R b/R/zzz.R
index 28b50d33..54374e09 100644
--- a/R/zzz.R
+++ b/R/zzz.R
@@ -11,7 +11,10 @@
 .tbbMallocProxyDllInfo <- NULL
 
 loadTbbLibrary <- function(name) {
-   
+   # TBB is statically linked on Windows
+   if (is_windows()) {
+      return(NULL)
+   }
    path <- tbbLibraryPath(name)
    if (is.null(path))
       return(NULL)