common: validate and properly parse floats

Fixes: #1665.

include/common/parse-double.h

@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef LABWC_PARSE_DOUBLE_H
+#define LABWC_PARSE_DOUBLE_H
+#include <assert.h>
+#include <stdbool.h>
+
+/**
+ * set_double() - Parse double-precision value of string.
+ * @str: String to parse
+ * @val: Storage for parsed value
+ *
+ * Return: true if string was parsed, false if not
+ *
+ * NOTE: If this function returns false, the value at *val will be untouched.
+ */
+bool set_double(const char *str, double *val);
+
+static inline bool
+set_float(const char *str, float *val)
+{
+	assert(val);
+
+	double d;
+	if (set_double(str, &d)) {
+		*val = d;
+		return true;
+	}
+
+	return false;
+}
+
+#endif /* LABWC_PARSE_DOUBLE_H */