base: utils: Add and use strtod() helper

The strtod() function is locale-dependent, and thus ill-suited to parse
numbers coming from, for instance, YAML files. The YamlObject class uses
strtod_l() to fix that issue, but that function is not available with
all libc implementations. Correctly handling this problem is becoming
out of scope for the YamlObject class.

As a first step, add a strtod() helper function in the utils namespace
that copies the implementation from YamlObject, and use it in
YamlObject. The core issue will then be fixed in utils::strtod().

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/base/utils.cpp

@@ -8,6 +8,7 @@
 #include <libcamera/base/utils.h>
 
 #include <iomanip>
+#include <locale.h>
 #include <sstream>
 #include <stdlib.h>
 #include <string.h>
@@ -463,6 +464,51 @@ std::string toAscii(const std::string &str)
  * \a b
  */
 
+namespace {
+
+/*
+ * RAII wrapper around locale_t instances, to support global locale instances
+ * without leaking memory.
+ */
+class Locale
+{
+public:
+	Locale(const char *locale)
+	{
+		locale_ = newlocale(LC_ALL_MASK, locale, static_cast<locale_t>(0));
+	}
+
+	~Locale()
+	{
+		freelocale(locale_);
+	}
+
+	locale_t locale() { return locale_; }
+
+private:
+	locale_t locale_;
+};
+
+Locale cLocale("C");
+
+} /* namespace */
+
+/**
+ * \brief Convert a string to a double independently of the current locale
+ * \param[in] nptr The string to convert
+ * \param[out] endptr Pointer to trailing portion of the string after conversion
+ *
+ * This function is a locale-independent version of the std::strtod() function.
+ * It behaves as the standard function, but uses the "C" locale instead of the
+ * current locale.
+ *
+ * \return The converted value, if any, or 0.0 if the conversion failed.
+ */
+double strtod(const char *__restrict nptr, char **__restrict endptr)
+{
+	return strtod_l(nptr, endptr, cLocale.locale());
+}
+
 } /* namespace utils */
 
 #ifndef __DOXYGEN__

src/libcamera/yaml_parser.cpp

@@ -31,38 +31,6 @@ namespace {
 /* Empty static YamlObject as a safe result for invalid operations */
 static const YamlObject empty;
 
-/*
- * Construct a global RAII locale for use by all YAML parser instances to
- * ensure consistency when parsing configuration files and types regardless of
- * the system locale configuration.
- *
- * For more information see:
- * - https://bugs.libcamera.org/show_bug.cgi?id=174
- */
-class Locale
-{
-public:
-	Locale(const char *locale)
-	{
-		locale_ = newlocale(LC_ALL_MASK, locale, static_cast<locale_t>(0));
-		if (locale_ == static_cast<locale_t>(0))
-			LOG(YamlParser, Fatal)
-				<< "Failed to construct a locale";
-	}
-
-	~Locale()
-	{
-		freelocale(locale_);
-	}
-
-	locale_t locale() { return locale_; }
-
-private:
-	locale_t locale_;
-};
-
-Locale yamlLocale("C");
-
 } /* namespace */
 
 /**
@@ -315,7 +283,7 @@ std::optional<double> YamlObject::get() const
 	char *end;
 
 	errno = 0;
-	double value = strtod_l(value_.c_str(), &end, yamlLocale.locale());
+	double value = utils::strtod(value_.c_str(), &end);
 
 	if ('\0' != *end || errno == ERANGE)
 		return std::nullopt;