From b3c4eab086d0455efcb907b31fe82632478ee093 Mon Sep 17 00:00:00 2001
From: Nick Christofides <118103879+NicChr@users.noreply.github.com>
Date: Tue, 7 Nov 2023 18:04:40 +0000
Subject: [PATCH] Rewrote rel_diff in C++.

---
 DESCRIPTION         |  2 +-
 R/cpp11.R           |  4 ++++
 R/diff.R            |  2 +-
 src/cpp11.cpp       |  8 ++++++++
 src/cpp_doubles.cpp | 29 +++++++++++++++++++++++++++++
 5 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/DESCRIPTION b/DESCRIPTION
index bf75746..8f9d958 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,6 +1,6 @@
 Package: cppdoubles
 Title: Fast Relative Comparisons of Floating Point Numbers in C++
-Version: 0.1.0
+Version: 0.1.0.9000
 Authors@R: 
     person("Nick", "Christofides", , "nick.christofides.r@gmail.com", role = c("aut", "cre"),
            comment = c(ORCID = "0000-0002-9743-7342"))
diff --git a/R/cpp11.R b/R/cpp11.R
index fa41ecd..867a80d 100644
--- a/R/cpp11.R
+++ b/R/cpp11.R
@@ -19,3 +19,7 @@ cpp_double_lt_vectorised <- function(x, y, tolerance) {
 cpp_double_lte_vectorised <- function(x, y, tolerance) {
   .Call(`_cppdoubles_cpp_double_lte_vectorised`, x, y, tolerance)
 }
+
+cpp_rel_diff_vectorised <- function(x, y) {
+  .Call(`_cppdoubles_cpp_rel_diff_vectorised`, x, y)
+}
diff --git a/R/diff.R b/R/diff.R
index 98ff5d9..2829305 100644
--- a/R/diff.R
+++ b/R/diff.R
@@ -13,7 +13,7 @@
 #' @rdname diff
 #' @export
 rel_diff <- function(x, y){
-  abs(x - y) / pmax(abs(x), abs(y))
+  .Call(`_cppdoubles_cpp_rel_diff_vectorised`, x, y)
 }
 #' @rdname diff
 #' @export
diff --git a/src/cpp11.cpp b/src/cpp11.cpp
index be6f469..7f88300 100644
--- a/src/cpp11.cpp
+++ b/src/cpp11.cpp
@@ -40,6 +40,13 @@ extern "C" SEXP _cppdoubles_cpp_double_lte_vectorised(SEXP x, SEXP y, SEXP toler
     return cpp11::as_sexp(cpp_double_lte_vectorised(cpp11::as_cpp<cpp11::decay_t<SEXP>>(x), cpp11::as_cpp<cpp11::decay_t<SEXP>>(y), cpp11::as_cpp<cpp11::decay_t<SEXP>>(tolerance)));
   END_CPP11
 }
+// cpp_doubles.cpp
+SEXP cpp_rel_diff_vectorised(SEXP x, SEXP y);
+extern "C" SEXP _cppdoubles_cpp_rel_diff_vectorised(SEXP x, SEXP y) {
+  BEGIN_CPP11
+    return cpp11::as_sexp(cpp_rel_diff_vectorised(cpp11::as_cpp<cpp11::decay_t<SEXP>>(x), cpp11::as_cpp<cpp11::decay_t<SEXP>>(y)));
+  END_CPP11
+}
 
 extern "C" {
 static const R_CallMethodDef CallEntries[] = {
@@ -48,6 +55,7 @@ static const R_CallMethodDef CallEntries[] = {
     {"_cppdoubles_cpp_double_gte_vectorised",   (DL_FUNC) &_cppdoubles_cpp_double_gte_vectorised,   3},
     {"_cppdoubles_cpp_double_lt_vectorised",    (DL_FUNC) &_cppdoubles_cpp_double_lt_vectorised,    3},
     {"_cppdoubles_cpp_double_lte_vectorised",   (DL_FUNC) &_cppdoubles_cpp_double_lte_vectorised,   3},
+    {"_cppdoubles_cpp_rel_diff_vectorised",     (DL_FUNC) &_cppdoubles_cpp_rel_diff_vectorised,     2},
     {NULL, NULL, 0}
 };
 }
diff --git a/src/cpp_doubles.cpp b/src/cpp_doubles.cpp
index af02028..6dd5322 100644
--- a/src/cpp_doubles.cpp
+++ b/src/cpp_doubles.cpp
@@ -255,3 +255,32 @@ SEXP cpp_double_lte_vectorised(SEXP x, SEXP y, SEXP tolerance) {
   Rf_unprotect(1);
   return out;
 }
+
+[[cpp11::register]]
+SEXP cpp_rel_diff_vectorised(SEXP x, SEXP y) {
+  // double tolerance = std::sqrt(std::numeric_limits<double>::epsilon());
+  R_xlen_t x_len = Rf_xlength(x);
+  R_xlen_t y_len = Rf_xlength(y);
+  R_xlen_t n = std::max(x_len, y_len);
+  if (x_len <= 0 || y_len <= 0){
+    // Avoid loop if any are length zero vectors
+    n = 0;
+  }
+  double *p_x = REAL(x);
+  double *p_y = REAL(y);
+  SEXP out = Rf_protect(Rf_allocVector(REALSXP, n));
+  double *p_out = REAL(out);
+  R_xlen_t xi;
+  R_xlen_t yi;
+  for (R_xlen_t i = 0; i < n; ++i) {
+    xi = i % x_len;
+    yi = i % y_len;
+    p_out[i] = cpp_double_rel_diff(p_x[xi], p_y[yi]);
+    // If either is NA, out is NA
+    if ( cpp_double_is_na(p_x[xi]) || cpp_double_is_na(p_y[yi]) ){
+      p_out[i] = NA_REAL;
+    }
+  }
+  Rf_unprotect(1);
+  return out;
+}