Fix pugixml float parsing local dependency

zeux/pugixml#469
troldal#133
using code from https://github.com/michael-hartmann/parsefloat

OpenXLSX/external/pugixml/pugixml.cpp

@@ -22,14 +22,7 @@
 #include <assert.h>
 #include <limits.h>
 
-#if (!defined(PUGIXML_HAS_CXX17)) && ((__cplusplus >= 201703L) || \
-     (defined(_MSC_VER) && _MSC_VER >= 1911 && _MSVC_LANG >= 201703L))
-#	define PUGIXML_HAS_CXX17
-#endif
 
-#if defined(PUGIXML_HAS_CXX17)
-#	include <charconv>
-#endif
 
 #ifdef PUGIXML_WCHAR_MODE
 #	include <wchar.h>
@@ -188,6 +181,147 @@ namespace pugi
 #	include <stdint.h>
 #endif
 
+
+
+// code from https://github.com/michael-hartmann/parsefloat
+#include <ctype.h>
+#include <math.h>
+#include <stdlib.h>
+
+#define USE_STR_TO_DOUBLE 1
+
+static double strtodouble(const char *str, int *success)
+{
+    double intpart = 0, fracpart = 0, exponent = 0;
+    int sign = +1, len = 0, conversion = 0;
+
+    // skip whitespace
+    while(isspace(*str))
+        str++;
+
+    // check for sign (optional; either + or -)
+    if(*str == '-')
+    {
+        sign = -1;
+        str++;
+    }
+    else if(*str == '+')
+        str++;
+
+    // check for nan and inf
+    if(tolower(str[0]) == 'n' && tolower(str[1]) == 'a' && tolower(str[2]) == 'n')
+    {
+        if(success != NULL)
+            *success = 1;
+        return NAN;
+    }
+    if(tolower(str[0]) == 'i' && tolower(str[1]) == 'n' && tolower(str[2]) == 'f')
+    {
+        if(success != NULL)
+            *success = 1;
+        return sign*INFINITY;
+    }
+
+    // find number of digits before decimal point
+    {
+        const char *p = str;
+        len = 0;
+        while(isdigit(*p))
+        {
+            p++;
+            len++;
+        }
+    }
+
+    if(len)
+        conversion = 1;
+
+    // convert intpart part of decimal point to a float
+    {
+        double f = 1;
+        for(int i = 0; i < len; i++)
+        {
+            int v = str[len-1-i] - '0';
+            intpart += v*f;
+            f *= 10;
+        }
+        str += len;
+    }
+
+    // check for decimal point (optional)
+    if(*str == '.')
+    {
+        const char *p = ++str;
+
+        // find number of digits after decimal point
+        len = 0;
+        while(isdigit(*p))
+        {
+            p++;
+            len++;
+        }
+
+        if(len)
+            conversion = 1;
+
+        // convert fracpart part of decimal point to a float
+        double f = 0.1;
+        for(int i = 0; i < len; i++)
+        {
+            int v = str[i] - '0';
+            fracpart += v*f;
+            f *= 0.1;
+        }
+
+        str = p;
+    }
+
+    if(conversion && (*str == 'e' || *str == 'E'))
+    {
+        int expsign = +1;
+        const char *p = ++str;
+
+        if(*p == '+')
+            p++;
+        else if(*p == '-')
+        {
+            expsign = -1;
+            p++;
+        }
+
+        str = p;
+        len = 0;
+        while(isdigit(*p))
+        {
+            len++;
+            p++;
+        }
+
+        int f = 1;
+        for(int i = 0; i < len; i++)
+        {
+            int v = str[len-1-i]-'0';
+            exponent += v*f;
+            f *= 10;
+        }
+
+        exponent *= expsign;
+    }
+
+    if(!conversion)
+    {
+        if(success != NULL)
+            *success = 0;
+        return NAN;
+    }
+
+    if(success != NULL)
+        *success = 1;
+
+    return sign*(intpart+fracpart)*pow(10, exponent);
+}
+
+
 // Memory allocation
 PUGI__NS_BEGIN
 PUGI__FN void* default_allocate(size_t size)
@@ -4600,10 +4734,8 @@ class xml_buffered_writer
 	#ifdef PUGIXML_WCHAR_MODE
 	    return wcstod(value, 0);
 	#else
-        #if defined(PUGIXML_HAS_CXX17)
-                double result_double = 0.0;
-                std::from_chars(value, (value + strlen(value)), result_double);
-                return result_double;
+        #if defined(USE_STR_TO_DOUBLE)
+                double result_double = strtodouble(value, NULL);
         #else
 	        return strtod(value, 0);
         #endif
@@ -4615,9 +4747,8 @@ class xml_buffered_writer
 	#ifdef PUGIXML_WCHAR_MODE
 	    return static_cast<float>(wcstod(value, 0));
 	#else
-        #if defined(PUGIXML_HAS_CXX17)
-                double result_double = 0.0;
-                std::from_chars(value, value + strlen(value), result_double);
+        #if defined(USE_STR_TO_DOUBLE)
+                double result_double = strtodouble(value, NULL);
                 return static_cast<float>(result_double);
         #else
 	        return static_cast<float>(strtod(value, 0));
@@ -8436,9 +8567,8 @@ PUGI__FN double convert_string_to_number(const char_t* string)
 	#ifdef PUGIXML_WCHAR_MODE
 	return wcstod(string, 0);
 	#else
-        #if defined(PUGIXML_HAS_CXX17)
-            double result_double = 0.0;
-            std::from_chars(string, string + strlen(string), result_double);
+        #if defined(USE_STR_TO_DOUBLE)
+            double result_double = strtodouble(value, NULL);
             return static_cast<float>(result_double);
         #else
 	        return strtod(string, 0);