LocalesUtils: fixed BSD and improved performance of decimal point formatting functions

src/libslic3r/LocalesUtils.cpp

@@ -1,7 +1,13 @@
 #include "LocalesUtils.hpp"
 
+#ifdef _WIN32
+    #include <charconv>
+#endif
 #include <stdexcept>
 
+#include <fast_float/fast_float.h>
+
+
 namespace Slic3r {
 
 
@@ -11,15 +17,15 @@ CNumericLocalesSetter::CNumericLocalesSetter()
     _configthreadlocale(_ENABLE_PER_THREAD_LOCALE);
     m_orig_numeric_locale = std::setlocale(LC_NUMERIC, nullptr);
     std::setlocale(LC_NUMERIC, "C");
-#elif __linux__
+#elif __APPLE__
+    m_original_locale = uselocale((locale_t)0);
+    m_new_locale = newlocale(LC_NUMERIC_MASK, "C", m_original_locale);
+    uselocale(m_new_locale);
+#else // linux / BSD
     m_original_locale = uselocale((locale_t)0);
     m_new_locale = duplocale(m_original_locale);
     m_new_locale = newlocale(LC_NUMERIC_MASK, "C", m_new_locale);
     uselocale(m_new_locale);
-#else // APPLE
-    m_original_locale = uselocale((locale_t)0);
-    m_new_locale = newlocale(LC_NUMERIC_MASK, "C", m_original_locale);
-    uselocale(m_new_locale);
 #endif
 }
 
@@ -48,25 +54,34 @@ bool is_decimal_separator_point()
 double string_to_double_decimal_point(const std::string& str, size_t* pos /* = nullptr*/)
 {
     double out;
-    std::istringstream stream(str);
-    if (! (stream >> out))
-        throw std::invalid_argument("string_to_double_decimal_point conversion failed.");
-    if (pos) {
-        if (stream.eof())
-            *pos = str.size();
-        else
-            *pos = stream.tellg();
-    }
+    size_t p = fast_float::from_chars(str.data(), str.data() + str.size(), out).ptr - str.data();
+    if (pos)
+        *pos = p;
     return out;
 }
 
 std::string float_to_string_decimal_point(double value, int precision/* = -1*/)
 {
+    // Our Windows build server fully supports C++17 std::to_chars. Let's use it.
+    // Other platforms are behind, fall back to slow stringstreams for now.
+#ifdef _WIN32
+    constexpr size_t SIZE = 20;
+    char out[SIZE] = "";
+    std::to_chars_result res;
+    if (precision >=0)
+        res = std::to_chars(out, out+SIZE, value, std::chars_format::fixed, precision);
+    else
+        res = std::to_chars(out, out+SIZE, value, std::chars_format::general, 6);
+    if (res.ec == std::errc::value_too_large)
+        throw std::invalid_argument("float_to_string_decimal_point conversion failed.");
+    return std::string(out, res.ptr - out);
+#else
     std::stringstream buf;
     if (precision >= 0)
         buf << std::fixed << std::setprecision(precision);
     buf << value;
     return buf.str();
+#endif
 }