Implement rev

Author: yutannihilation

R/hello.R

@@ -18,6 +18,14 @@ hello2 <- function(name) {
   .Call(hello_wrapper2, name)
 }
 
+#' @export
+#' @rdname hellorust
+#' @examples rev()
+#' @useDynLib hellorust rev_wrapper
+rev <- function(x) {
+  .Call(rev_wrapper, x)
+}
+
 #' @export
 #' @rdname hellorust
 #' @examples random()

src/myrustlib/api.h

@@ -4,8 +4,16 @@
 extern "C" {
 #endif
 
+// A struct to pass the results from Rust to C
+typedef struct
+{
+  double *data;
+  uint32_t len;
+} Slice;
+
 char * string_from_rust();
 char * string_from_rust2(const char*);
+Slice rev_slice(Slice);
 int32_t random_number();
 void run_threads();
 

src/myrustlib/src/lib.rs

@@ -6,8 +6,12 @@ extern crate rand;
 mod hello;
 mod random;
 mod mythreads;
+mod slice;
 
 // Export functions called by R
 pub use hello::string_from_rust;
+pub use hello::string_from_rust2;
 pub use random::random_number;
 pub use mythreads::run_threads;
+pub use slice::rev_slice;
+pub use slice::Slice;

src/myrustlib/src/slice.rs

@@ -0,0 +1,26 @@
+use std;
+use std::os::raw::{c_double, c_uint};
+
+#[repr(C)]
+pub struct Slice {
+    data: *mut c_double,
+    len: c_uint,
+}
+
+#[no_mangle]
+pub extern fn rev_slice(s: Slice) -> Slice {
+    // convert from Slice to Rust slice
+    let s = unsafe { std::slice::from_raw_parts_mut(s.data, s.len as _) };
+
+    let mut v = s.to_vec();
+    v.reverse();
+    let len = v.len();
+
+    let v_ptr = v.as_mut_ptr();
+    std::mem::forget(v);
+
+    Slice {
+        data: v_ptr,
+        len: len as _,
+    }
+}

src/wrapper.c

@@ -15,6 +15,19 @@ SEXP hello_wrapper2(SEXP name){
   return Rf_ScalarString(Rf_mkCharCE(res, CE_UTF8));
 }
 
+SEXP rev_wrapper(SEXP x){
+  Slice s = {REAL(x), Rf_length(x)};
+  Slice s_rev = rev_slice(s);
+
+  SEXP out = PROTECT(Rf_allocVector(REALSXP, s_rev.len));
+  for (int i = 0; i < s_rev.len; i++) {
+    SET_REAL_ELT(out, i, s_rev.data[i]);
+  }
+  UNPROTECT(1);
+
+  return out;
+}
+
 
 SEXP random_wrapper(){
   return Rf_ScalarInteger(random_number());
@@ -29,6 +42,7 @@ SEXP threads_wapper(){
 static const R_CallMethodDef CallEntries[] = {
   {"hello_wrapper", (DL_FUNC) &hello_wrapper, 0},
   {"hello_wrapper2", (DL_FUNC) &hello_wrapper2, 0},
+  {"rev_wrapper", (DL_FUNC) &rev_wrapper, 0},
   {"random_wrapper", (DL_FUNC) &random_wrapper, 0},
   {"threads_wapper", (DL_FUNC) &threads_wapper, 0},
   {NULL, NULL, 0}