add Chapter18

Chapter18/cib/libs/stdx/numeric.hpp

@@ -0,0 +1,71 @@
+#pragma once
+
+#include <algorithm>
+#include <functional>
+#include <limits>
+#include <type_traits>
+#include <utility>
+
+namespace stdx {
+inline namespace v1 {
+#if __cplusplus >= 202002L
+#define CONSTEXPR_INVOKE constexpr
+#else
+#define CONSTEXPR_INVOKE
+#endif
+
+template <typename T, typename InputIt, typename ROp, typename TOp,
+          typename... InputItN>
+CONSTEXPR_INVOKE auto transform_reduce(InputIt first, InputIt last, T init,
+                                       ROp rop, TOp top,
+                                       InputItN... first_n) -> T {
+    while (first != last) {
+        init = std::invoke(rop, std::move(init),
+                           std::invoke(top, *first, *first_n...));
+        static_cast<void>(++first), (static_cast<void>(++first_n), ...);
+    }
+    return init;
+}
+
+template <typename T, typename InputIt, typename Size, typename ROp,
+          typename TOp, typename... InputItN>
+CONSTEXPR_INVOKE auto transform_reduce_n(InputIt first, Size n, T init, ROp rop,
+                                         TOp top, InputItN... first_n) -> T {
+    while (n-- != 0) {
+        init = std::invoke(rop, std::move(init),
+                           std::invoke(top, *first, *first_n...));
+        static_cast<void>(++first), (static_cast<void>(++first_n), ...);
+    }
+    return init;
+}
+#undef CONSTEXPR_INVOKE
+
+template <typename To, typename From>
+constexpr auto saturate_cast(From from) -> To {
+    constexpr auto to_min = std::numeric_limits<To>::min();
+    constexpr auto to_max = std::numeric_limits<To>::max();
+
+    if constexpr (sizeof(From) > sizeof(To)) {
+        auto const clamped = std::clamp<From>(from, to_min, to_max);
+        return static_cast<To>(clamped);
+    }
+
+    if constexpr (sizeof(From) == sizeof(To)) {
+        if constexpr (std::is_unsigned_v<From> and std::is_signed_v<To>) {
+            if (from > to_max) {
+                return to_max;
+            }
+        }
+
+        if constexpr (std::is_signed_v<From> and std::is_unsigned_v<To>) {
+            if (from < 0) {
+                return static_cast<To>(0);
+            }
+        }
+    }
+
+    return static_cast<To>(from);
+}
+
+} // namespace v1
+} // namespace stdx