Merge pull request #106 from elbeno/bitset-difference

Add bitset `operator-` (set difference)
intel · Jun 3, 2024 · d2c0ba3 · d2c0ba3
2 parents 44c5b74 + 7e45a91
commit d2c0ba3
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diff --git a/docs/bitset.adoc b/docs/bitset.adoc
@@ -68,3 +68,6 @@ auto bs = stdx::bitset<11>{0b101}; // 11 bits, value 5
 auto i = bs.to<std::uint64_t>();   // 5 (a std::uint64_t)
 auto j = bs.to_natural();          // 5 (a std::uint16_t)
 ----
+
+Bitsets support all the usual bitwise operators (`and`, `or`, `xor` and `not`)
+and also support `operator-` meaning set difference, or `a & ~b`.
diff --git a/include/stdx/bitset.hpp b/include/stdx/bitset.hpp
@@ -84,6 +84,11 @@ template <std::size_t N, typename StorageElem> class bitset {
         return lhs;
     }
 
+    friend constexpr auto operator-(bitset const &lhs, bitset rhs) -> bitset {
+        rhs.flip();
+        return lhs & rhs;
+    }
+
     friend constexpr auto operator<<(bitset lhs, std::size_t pos) -> bitset {
         lhs <<= pos;
         return lhs;

diff --git a/test/bitset.cpp b/test/bitset.cpp
@@ -227,6 +227,13 @@ TEMPLATE_TEST_CASE("not", "[bitset]", std::uint8_t, std::uint16_t,
     static_assert(~bs == stdx::bitset<3, TestType>{0b10ul});
 }
 
+TEMPLATE_TEST_CASE("difference", "[bitset]", std::uint8_t, std::uint16_t,
+                   std::uint32_t, std::uint64_t) {
+    constexpr auto bs1 = stdx::bitset<3, TestType>{0b101ul};
+    constexpr auto bs2 = stdx::bitset<3, TestType>{0b011ul};
+    static_assert(bs1 - bs2 == stdx::bitset<3, TestType>{0b100ul});
+}
+
 TEMPLATE_TEST_CASE("left shift", "[bitset]", std::uint8_t, std::uint16_t,
                    std::uint32_t, std::uint64_t) {
     constexpr auto bs = stdx::bitset<3, TestType>{0b101ul};