Use locale-independent string->float conversion (#4885)

* Use locale-independent string->float conversion

strtof and friends are locale aware and won't parse decimal numbers
with a period ("12.6" for instance) in locales that use another
character for the decimal period ("," in French for instance).

This change introduces a new function called strtof_c that forces
the use of a specific locale (called "C") to make sure we always
parse floats in the desired "C" format ("12.6").

With C++17 we should be able to use std::from_chars but this API
is not implemented in clang for floats at the moment.

* Fix Linux

libs/utils/src/string.cpp

@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <utils/string.h>
+
+#include <stdlib.h>
+#if defined(WIN32)
+#    include <locale.h>
+#elif defined(__linux__)
+#    include <locale.h>
+#else
+#    include <xlocale.h>
+#endif
+
+#include <mutex>
+
+namespace utils {
+
+#if defined(WIN32)
+
+_locale_t sLocaleC;
+std::once_flag sLocaleCOnceFlag;
+
+_locale_t get_c_locale() {
+    std::call_once(sLocaleCOnceFlag, []() {
+        sLocaleC = _create_locale(LC_ALL, "C");
+    });
+    return sLocaleC;
+}
+
+float strtof_c(const char* start, char** end) {
+    return _strtof_l(start, end, get_c_locale());
+}
+
+#else // if defined(WIN32)
+
+locale_t sLocaleC;
+std::once_flag sLocaleCOnceFlag;
+
+locale_t get_c_locale() {
+    std::call_once(sLocaleCOnceFlag, []() {
+        sLocaleC = newlocale(LC_ALL_MASK, "C", nullptr);
+    });
+    return sLocaleC;
+}
+
+float strtof_c(const char* start, char** end) {
+    return strtof_l(start, end, get_c_locale());
+}
+
+#endif
+
+} // namespace utils