Date subsecond rounding; fixes #187 (#290)

* Date subsecond rounding; fixes #187

* Add a source for the rounding sol'n; re-save test sheets just to be safe

src/XlsCell.h

@@ -5,6 +5,7 @@
 #include <libxls/xls.h>
 #include <libxls/xlstypes.h>
 #include "ColSpec.h"
+#include "utils.h"
 
 // Key reference for understanding the structure of the xls format is
 // [MS-XLS]: Excel Binary File Format (.xls) Structure
@@ -287,7 +288,7 @@ class XlsCell {
 
     case CELL_DATE:
     case CELL_NUMERIC:
-      return (cell_->d - offset) * 86400;
+      return dateRound((cell_->d - offset) * 86400);
     }
   }
 

src/XlsxCell.h

@@ -268,7 +268,7 @@ class XlsxCell {
     case CELL_NUMERIC:
     {
       rapidxml::xml_node<>* v = cell_->first_node("v");
-      return (atof(v->value()) - offset) * 86400;
+      return dateRound((atof(v->value()) - offset) * 86400);
     }
     }
   }

src/utils.h

@@ -18,6 +18,17 @@ inline double dateOffset(bool is1904) {
   return is1904 ? 24107 : 25569;
 }
 
+// this is sort of horrible
+// convert serial date to decimilliseconds
+// use well-known hack to round to nearest integer w/o C++11 or boost, e.g.
+// http://stackoverflow.com/questions/485525/round-for-float-in-c
+// convert back to serial date
+inline double dateRound(double dttm) {
+  double ms = dttm * 10000;
+  ms = (ms >= 0.0 ? std::floor(ms + 0.5) : std::ceil(ms - 0.5));
+  return ms / 10000;
+}
+
 // Simple parser: does not check that order of numbers and letters is correct
 inline std::pair<int, int> parseRef(const char* ref) {
   int col = 0, row = 0;

tests/testthat/test-dates.R

@@ -10,3 +10,14 @@ test_that("dates respect worksheet date setting", {
   expect_equal(d1900, d1900loo)
   expect_equal(d1900$X1, ISOdate(2000, 01, 01, 0, tz = "UTC"))
 })
+
+## #187 Date/times missing a second
+test_that("date subsecond rounding works", {
+  ## xlsx
+  df <- read_excel(test_sheet("datetime-rounding.xlsx"))
+  expect_identical(as.character(df$dttm), df$dttm_string)
+
+  ## xls
+  df <- read_excel(test_sheet("datetime-rounding.xls"))
+  expect_identical(as.character(df$dttm), df$dttm_string)
+})