pitrou commented on a change in pull request #11919:
URL: https://github.com/apache/arrow/pull/11919#discussion_r772294483
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File path: r/src/arrow_cpp11.h
##########
@@ -57,13 +57,45 @@ namespace r {
template <typename T>
struct Pointer {
Pointer() : ptr_(new T()) {}
- explicit Pointer(SEXP x)
- : ptr_(reinterpret_cast<T*>(static_cast<uintptr_t>(REAL(x)[0]))) {}
+ explicit Pointer(SEXP x) {
+ if (TYPEOF(x) == EXTPTRSXP) {
+ ptr_ = (T*)R_ExternalPtrAddr(x);
+ } else if (TYPEOF(x) == STRSXP && Rf_length(x) == 1) {
+ // User passed a character representation of the pointer address
+ SEXP char0 = STRING_ELT(x, 0);
+ if (char0 == NA_STRING) {
+ cpp11::stop("Can't convert NA_character_ to pointer");
+ }
+
+ const char* input_chars = CHAR(char0);
+ char* endptr;
+ uint64_t ptr_value = strtoull(input_chars, &endptr, 0);
+ if (endptr != (input_chars + strlen(input_chars))) {
+ cpp11::stop("Can't parse '%s' as a 64-bit integer address",
input_chars);
+ }
- inline operator SEXP() const {
- return
Rf_ScalarReal(static_cast<double>(reinterpret_cast<uintptr_t>(ptr_)));
+ ptr_ = reinterpret_cast<T*>(static_cast<uintptr_t>(ptr_value));
+ } else if (Rf_inherits(x, "integer64") && Rf_length(x) == 1) {
+ // User passed an integer64(1) of the pointer address
+ // an integer64 is a REALSXP under the hood, with the bytes
+ // of each double reinterpreted as an int64.
+ uint64_t ptr_value;
+ memcpy(&ptr_value, REAL(x), sizeof(uint64_t));
+ ptr_ = reinterpret_cast<T*>(static_cast<uintptr_t>(ptr_value));
Review comment:
I don't know whether the assignment would be optimized away, but
assignments between CPU registers are practically costless.
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