allow opt-out from Boost.SIMD

Author: jjallaire

R/build.R

@@ -49,8 +49,8 @@ tbbCxxFlags <- function(simd = TRUE) {
       flags <- paste(flags, "-DRCPP_PARALLEL_USE_TBB=1")
 
    # reflect requested use of boost::simd
-   if (isTRUE(simd))
-      flags <- paste(flags, "-DRCPP_PARALLEL_USE_SIMD=1")
+   if (!simd)
+      flags <- paste(flags, "-DRCPP_PARALLEL_USE_SIMD=0")
 
    flags
 }

examples/simd-operations.Rmd

@@ -156,8 +156,24 @@ The two `transformDataImpl` functions have the same name, but only one will be c
 
 Note that if you conditionally compile all uses of Boost.SIMD within your package then you can actually drop the `C++11` from `SystemRequirements` (it's no longer required as a result of your fallback implementation).
 
+## Disabling SIMD
 
+If you don't want to use Boost.SIMD at all you can explicitly disable it as follows:
 
+1. For `sourceCpp` you can define `RCPP_PARALLEL_USE_TBB`:
+
+    ```cpp
+    #define RCPP_PARALLEL_USE_TBB 0
+    ```
+
+2. For R packages you can pass `simd = FALSE` to the CxxFlags function:
+
+    ```make
+    PKG_CXXFLAGS += $(shell ${R_HOME}/bin/Rscript -e "RcppParallel::CxxFlags(simd = FALSE)")
+    ```
+   
+
+   
 
 
 

inst/include/RcppParallel.h

@@ -52,9 +52,11 @@ inline void parallelReduce(std::size_t begin, std::size_t end,
 
 } // namespace RcppParallel
 
-// Enable SIMD if requested (requires C++11)
-#if RCPP_PARALLEL_USE_SIMD && (__cplusplus <= 199711L)
-  #undef RCPP_PARALLEL_USE_SIMD
+// Auto enable/disable SIMD unless it's been explicitly set (requires C++11)
+#ifndef RCPP_PARALLEL_USE_SIMD
+#if (__cplusplus > 199711L)
+      #define RCPP_PARALLEL_USE_SIMD 1
+   #endif
 #endif
 #if RCPP_PARALLEL_USE_SIMD
   #include "RcppParallel/SIMD.h"