1 files changed, 90 insertions, 0 deletions
diff --git a/nihil.core/parse_size.ccm b/nihil.core/parse_size.ccm
new file mode 100644
index 0000000..5f80755
--- /dev/null
+++ b/nihil.core/parse_size.ccm
@@ -0,0 +1,90 @@
+// This source code is released into the public domain.
+export module nihil.core:parse_size;
+
+import nihil.std;
+
+import :ctype;
+import :errc;
+import :error;
+import :monad;
+
+namespace nihil {
+
+export template <typename Char>
+auto get_multiplier(Char c) -> std::expected<std::uint64_t, error>
+{
+	auto ret = std::uint64_t{1};
+
+	// clang-format off
+	switch (c) {
+	case 'p': case 'P': ret *= 1024;	// NOLINT
+	case 't': case 'T': ret *= 1024;	// NOLINT
+	case 'g': case 'G': ret *= 1024;	// NOLINT
+	case 'm': case 'M': ret *= 1024;	// NOLINT
+	case 'k': case 'K': ret *= 1024;	// NOLINT
+		return ret;
+
+	default:
+		return error(errc::invalid_unit);
+	}
+	// clang-format on
+}
+
+// Parse a string containing a human-formatted size, such as "1024"
+// or "4g".  Parsing is always done in the "C" locale and does not
+// recognise thousands separators or negative numbers.
+export template <typename T, typename Char>
+[[nodiscard]]
+auto parse_size(std::basic_string_view<Char> str) -> std::expected<T, error>
+{
+	// Extract the numeric part of the string.
+	auto it = std::ranges::find_if_not(str, is_c_digit);
+	auto num_str = std::basic_string_view<Char>(std::ranges::begin(str), it);
+
+	if (num_str.empty())
+		co_return error(errc::empty_string);
+
+	auto ret = T{0};
+
+	for (auto c : num_str) {
+		if (ret > (std::numeric_limits<T>::max() / 10))
+			co_return error(std::errc::result_out_of_range);
+		ret *= 10;
+
+		auto digit = static_cast<T>(c - '0');
+		if ((std::numeric_limits<T>::max() - digit) < ret)
+			co_return error(std::errc::result_out_of_range);
+		ret += digit;
+	}
+
+	if (it == str.end())
+		// No multiplier.
+		co_return ret;
+
+	auto mchar = *it++;
+
+	if (it != str.end())
+		// Multiplier is more than one character.
+		co_return error(errc::invalid_unit);
+
+	auto mult = co_await get_multiplier(mchar);
+
+	if (std::cmp_greater(ret, std::numeric_limits<T>::max() / mult))
+		co_return error(std::errc::result_out_of_range);
+
+	co_return ret *mult;
+}
+
+export template <typename T>
+[[nodiscard]] auto parse_size(char const *s)
+{
+	return parse_size<T>(std::string_view(s));
+}
+
+export template <typename T>
+[[nodiscard]] auto parse_size(wchar_t const *s)
+{
+	return parse_size<T>(std::wstring_view(s));
+}
+
+} // namespace nihil