From f03298e76d76914de056b57412f722a806a0af50 Mon Sep 17 00:00:00 2001
From: Ben Deane <ben@elbeno.com>
Date: Sat, 15 Feb 2025 01:16:30 -0700
Subject: [PATCH] :bug: Fix `sized` issue with indivisible sizes

Problem:
- `sized` does not work correctly when the sizes of `T` and `U` are not
  multiples, for example when computing the number of 4-byte values required to
  hold N 3-byte values.

Solution:
- Fix it.
---
 include/stdx/utility.hpp |  2 +-
 test/utility.cpp         | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/include/stdx/utility.hpp b/include/stdx/utility.hpp
index c138b96..8a1a71b 100644
--- a/include/stdx/utility.hpp
+++ b/include/stdx/utility.hpp
@@ -116,7 +116,7 @@ template <typename T, typename U>
     if constexpr (sizeof(T) == sizeof(U)) {
         return sz;
     } else if constexpr (sizeof(T) > sizeof(U)) {
-        return sz * (sizeof(T) / sizeof(U));
+        return (sz * sizeof(T) / sizeof(U)) + (sizeof(T) % sizeof(U) & 1u);
     } else {
         return (sz * sizeof(T) + sizeof(U) - 1) / sizeof(U);
     }
diff --git a/test/utility.cpp b/test/utility.cpp
index c13b48c..df96466 100644
--- a/test/utility.cpp
+++ b/test/utility.cpp
@@ -3,6 +3,7 @@
 #include <catch2/catch_template_test_macros.hpp>
 #include <catch2/catch_test_macros.hpp>
 
+#include <array>
 #include <cstdint>
 #include <string_view>
 #include <type_traits>
@@ -130,6 +131,18 @@ TEST_CASE("sized<T> aliases", "[utility]") {
     static_assert(stdx::sized64{1}.in<std::uint64_t>() == 1);
 }
 
+TEST_CASE("sized<T> in (downsize not divisible)", "[utility]") {
+    using T = std::array<char, 3>;
+    static_assert(sizeof(T) == 3);
+    static_assert(stdx::sized<std::uint32_t>{2}.in<T>() == 3);
+}
+
+TEST_CASE("sized<T> in (upsize not divisible)", "[utility]") {
+    using T = std::array<char, 3>;
+    static_assert(sizeof(T) == 3);
+    static_assert(stdx::sized<T>{3}.in<std::uint32_t>() == 3);
+}
+
 TEST_CASE("CX_VALUE structural value", "[utility]") {
     auto x = CX_VALUE(42);
     static_assert(x() == 42);