From e059d259c7f1e37019b2b49ed568b8851447ee9e Mon Sep 17 00:00:00 2001
From: JCrawfy <joshcrawfy@gmail.com>
Date: Sat, 16 Nov 2019 14:18:33 +1300
Subject: [PATCH] specialise number_converter when strtod_l is available

in load benchmark, not using the specialisation adds ~10% to execution time
---
 source/detail/serialization/xlsx_consumer.cpp | 63 +++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/source/detail/serialization/xlsx_consumer.cpp b/source/detail/serialization/xlsx_consumer.cpp
index 54850a6f..381c7b5e 100644
--- a/source/detail/serialization/xlsx_consumer.cpp
+++ b/source/detail/serialization/xlsx_consumer.cpp
@@ -107,6 +107,69 @@ bool is_true(const std::string &bool_string)
 #endif
 }
 
+// can find documentation for _strtod_l back to VS 2015
+// https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/strtod-strtod-l-wcstod-wcstod-l?view=vs-2015
+//
+#if defined(_MSC_VER) && _MSC_VER >= 1900
+
+#include <locale.h>
+#include <stdlib.h>
+
+// Cache locale object
+static int c_locale_initialized = 0;
+static _locale_t c_locale;
+
+_locale_t get_c_locale()
+{
+    if (!c_locale_initialized)
+    {
+        c_locale_initialized = 1;
+        c_locale = _create_locale(LC_ALL, "C");
+    }
+    return c_locale;
+}
+
+double strtod_c(const char *nptr, char **endptr)
+{
+    return _strtod_l(nptr, endptr, get_c_locale());
+}
+
+struct number_converter
+{
+    double stold(const std::string &s)
+    {
+        return strtod_c(s.c_str(), nullptr);
+    }
+};
+
+#else
+
+// according to various sources, something like the below *would* work for POSIX systems
+// however due to uncertainty on whether it will actually work it is not used
+//#include <stdlib.h>
+//#include <xlocale.h>
+//
+//// Cache locale object
+//static int c_locale_initialized = 0;
+//static locale_t c_locale;
+//
+//locale_t get_c_locale()
+//{
+//    if (!c_locale_initialized)
+//    {
+//        c_locale_initialized = 1;
+//        c_locale = newlocale(LC_ALL_MASK, "C", NULL);
+//    }
+//    return c_locale;
+//}
+//
+//double strtod_c(const char *nptr, char **endptr)
+//{
+//    return strtod_l(nptr, endptr, get_c_locale());
+//}
+
+// add specialisations whenever possible
+// in the spreadsheet-load benchmark, strtod is roughly 10% faster
 struct number_converter
 {
     number_converter()