math: add

Signed-off-by: Simon Rozman <simon@rozman.si>

include/stdex/math.hpp

@@ -0,0 +1,49 @@
+/*
+	SPDX-License-Identifier: MIT
+	Copyright © 2023 Amebis
+*/
+
+#pragma once
+
+#include "sal.hpp"
+#include "system.hpp"
+#include <stdexcept>
+
+namespace stdex
+{
+	inline size_t mul(size_t a, size_t b)
+	{
+#if _MSC_VER >= 1300
+		SIZE_T result;
+		if (SUCCEEDED(SIZETMult(a, b, &result)))
+			return result;
+#elif defined(_MSC_VER)
+		if (a == 0)
+			return 0;
+		if (b <= SIZE_MAX / a)
+			return a * b;
+#else
+		size_t result;
+		if (!__builtin_mul_overflow(a, b, &result))
+			return result;
+#endif
+		throw std::invalid_argument("multiply overflow");
+	}
+
+	inline size_t add(size_t a, size_t b)
+	{
+#if _MSC_VER >= 1300
+		SIZE_T result;
+		if (SUCCEEDED(SIZETAdd(a, b, &result)))
+			return result;
+#elif defined(_MSC_VER)
+		if (a <= SIZE_MAX - b)
+			return a + b;
+#else
+		size_t result;
+		if (!__builtin_add_overflow(a, b, &result))
+			return result;
+#endif
+		throw std::invalid_argument("add overflow");
+	}
+}