From 7951befa5d0af0abcb54d151e4c11f7556200392 Mon Sep 17 00:00:00 2001
From: Ben Deane <ben@elbeno.com>
Date: Wed, 4 Feb 2026 12:08:33 -0700
Subject: [PATCH] :bug: Fix bitset construction

Problem:
- When a `bitset` has zero size, it cannot be constructed with `all_bits`.

Solution:
- Check for zero size in fixing up the end bits.
---
 include/stdx/bitset.hpp | 4 +++-
 test/bitset.cpp         | 2 ++
 test/type_bitset.cpp    | 1 +
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/stdx/bitset.hpp b/include/stdx/bitset.hpp
index 7df348c..04bfc0f 100644
--- a/include/stdx/bitset.hpp
+++ b/include/stdx/bitset.hpp
@@ -175,7 +175,9 @@ class bitset {
         for (auto &elem : storage) {
             elem = allbits;
         }
-        storage.back() &= lastmask;
+        if constexpr (N > 0) {
+            storage.back() &= lastmask;
+        }
     }
 
     constexpr explicit bitset(std::string_view str, std::size_t pos = 0,
diff --git a/test/bitset.cpp b/test/bitset.cpp
index e3485ee..065caef 100644
--- a/test/bitset.cpp
+++ b/test/bitset.cpp
@@ -516,4 +516,6 @@ TEST_CASE("zero size bitset", "[bitset]") {
     CHECK(bs3.to<std::uint8_t>() == 0);
     bs3 >>= 1;
     CHECK(bs3.to<std::uint8_t>() == 0);
+    bs3 = stdx::bitset<0>{stdx::all_bits};
+    CHECK(bs3.to<std::uint8_t>() == 0);
 }
diff --git a/test/type_bitset.cpp b/test/type_bitset.cpp
index 1b52453..adc774c 100644
--- a/test/type_bitset.cpp
+++ b/test/type_bitset.cpp
@@ -10,6 +10,7 @@
 #include <type_traits>
 
 TEST_CASE("bitset size", "[type_bitset]") {
+    STATIC_CHECK(stdx::type_bitset<>{}.size() == 0u);
     STATIC_CHECK(stdx::type_bitset<int>{}.size() == 1u);
     STATIC_CHECK(stdx::type_bitset<int, float>{}.size() == 2u);
 }