Update playlist file parsing, reduce allocs (#1157)

* Update playlist file parsing, reduce allocs
* Cleanup, move impl to cpp

firmware/common/convert.hpp

@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2023 Kyle Reed
+ *
+ * This file is part of PortaPack.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __CONVERT_H__
+#define __CONVERT_H__
+
+#include <charconv>
+#include <cstdlib>
+#include <string>
+#include <string_view>
+#include <type_traits>
+
+/* Zero-allocation conversion helper. */
+/* Notes:
+ * - T must be an integer type.
+ * - For base 16, input _must not_ contain a '0x' or '0X' prefix.
+ * - For base 8 a leading 0 on the literal is allowed.
+ * - Leading whitespce will cause the parse to fail.
+ */
+// TODO: from_chars seems to cause code bloat.
+// Look into using strtol and friends instead.
+
+template <typename T>
+std::enable_if_t<std::is_integral_v<T>, bool> parse_int(std::string_view str, T& out_val, int base = 10) {
+    auto result = std::from_chars(str.data(), str.data() + str.length(), out_val, base);
+    return static_cast<int>(result.ec) == 0;
+}
+
+#endif /*__CONVERT_H__*/