1 files changed, 107 insertions, 0 deletions
diff --git a/nihil.util/parse_size.ccm b/nihil.util/parse_size.ccm
new file mode 100644
index 0000000..c95ac50
--- /dev/null
+++ b/nihil.util/parse_size.ccm
@@ -0,0 +1,107 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+module;
+
+#include <algorithm>
+#include <coroutine>
+#include <cstdint>
+#include <expected>
+#include <ranges>
+#include <string>
+#include <system_error>
+#include <utility>
+
+export module nihil.util:parse_size;
+
+import nihil.core;
+import nihil.error;
+import nihil.monad;
+
+import :ctype;
+
+namespace nihil {
+
+template<typename Char>
+auto get_multiplier(Char c) -> std::expected<std::uint64_t, error>
+{
+	auto ret = std::uint64_t{1};
+
+	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 std::unexpected(error(errc::invalid_unit));
+	}
+}
+
+/*
+ * 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 std::unexpected(error(errc::empty_string));
+
+	auto ret = T{0};
+
+	for (auto c : num_str) {
+		if (ret > (std::numeric_limits<T>::max() / 10))
+			co_return std::unexpected(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 std::unexpected(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 std::unexpected(error(errc::invalid_unit));
+
+	auto mult = co_await get_multiplier(mchar);
+
+	if (std::cmp_greater(ret, std::numeric_limits<T>::max() / mult))
+		co_return std::unexpected(error(
+				std::errc::result_out_of_range));
+
+	co_return ret * mult;
+}
+
+export template<typename T>
+[[nodiscard]] inline auto parse_size(char const *s)
+{
+	return parse_size<T>(std::string_view(s));
+}
+
+export template<typename T>
+[[nodiscard]] inline auto parse_size(wchar_t const *s)
+{
+	return parse_size<T>(std::wstring_view(s));
+}
+
+}