Make remaining simple functions constexpr (#305)

include/intx/intx.hpp

@@ -270,24 +270,24 @@ inline constexpr uint128 operator-(uint128 x) noexcept
     return 0 - x;
 }
 
-inline uint128& operator++(uint128& x) noexcept
+inline constexpr uint128& operator++(uint128& x) noexcept
 {
     return x = x + 1;
 }
 
-inline uint128& operator--(uint128& x) noexcept
+inline constexpr uint128& operator--(uint128& x) noexcept
 {
     return x = x - 1;
 }
 
-inline const uint128 operator++(uint128& x, int) noexcept  // NOLINT(readability-const-return-type)
+inline constexpr const uint128 operator++(uint128& x, int) noexcept  // NOLINT(*-const-return-type)
 {
     const auto ret = x;
     ++x;
     return ret;
 }
 
-inline const uint128 operator--(uint128& x, int) noexcept  // NOLINT(readability-const-return-type)
+inline constexpr const uint128 operator--(uint128& x, int) noexcept  // NOLINT(*-const-return-type)
 {
     const auto ret = x;
     --x;
@@ -593,6 +593,8 @@ struct div_result
     QuotT quot;
     RemT rem;
 
+    bool operator==(const div_result&) const = default;
+
     /// Conversion to tuple of references, to allow usage with std::tie().
     constexpr operator std::tuple<QuotT&, RemT&>() noexcept { return {quot, rem}; }
 };
@@ -627,7 +629,7 @@ constexpr uint16_t reciprocal_table[] = {REPEAT256()};
 /// Computes the reciprocal (2^128 - 1) / d - 2^64 for normalized d.
 ///
 /// Based on Algorithm 2 from "Improved division by invariant integers".
-inline uint64_t reciprocal_2by1(uint64_t d) noexcept
+inline constexpr uint64_t reciprocal_2by1(uint64_t d) noexcept
 {
     INTX_REQUIRE(d & 0x8000000000000000);  // Must be normalized.
 
@@ -648,7 +650,7 @@ inline uint64_t reciprocal_2by1(uint64_t d) noexcept
     return v4;
 }
 
-inline uint64_t reciprocal_3by2(uint128 d) noexcept
+inline constexpr uint64_t reciprocal_3by2(uint128 d) noexcept
 {
     auto v = reciprocal_2by1(d[1]);
     auto p = d[1] * v;
@@ -679,7 +681,7 @@ inline uint64_t reciprocal_3by2(uint128 d) noexcept
     return v;
 }
 
-inline div_result<uint64_t> udivrem_2by1(uint128 u, uint64_t d, uint64_t v) noexcept
+inline constexpr div_result<uint64_t> udivrem_2by1(uint128 u, uint64_t d, uint64_t v) noexcept
 {
     auto q = umul(v, u[1]);
     q = fast_add(q, u);
@@ -703,7 +705,7 @@ inline div_result<uint64_t> udivrem_2by1(uint128 u, uint64_t d, uint64_t v) noex
     return {q[1], r};
 }
 
-inline div_result<uint64_t, uint128> udivrem_3by2(
+inline constexpr div_result<uint64_t, uint128> udivrem_3by2(
     uint64_t u2, uint64_t u1, uint64_t u0, uint128 d, uint64_t v) noexcept
 {
     auto q = umul(v, u2);
@@ -733,7 +735,7 @@ inline div_result<uint64_t, uint128> udivrem_3by2(
     return {q[1], r};
 }
 
-inline div_result<uint128> udivrem(uint128 x, uint128 y) noexcept
+inline constexpr div_result<uint128> udivrem(uint128 x, uint128 y) noexcept
 {
     if (y[1] == 0)
     {
@@ -778,7 +780,7 @@ inline div_result<uint128> udivrem(uint128 x, uint128 y) noexcept
     return {res.quot, res.rem >> lsh};
 }
 
-inline div_result<uint128> sdivrem(uint128 x, uint128 y) noexcept
+inline constexpr div_result<uint128> sdivrem(uint128 x, uint128 y) noexcept
 {
     constexpr auto sign_mask = uint128{1} << 127;
     const auto x_is_neg = (x & sign_mask) != 0;
@@ -794,22 +796,22 @@ inline div_result<uint128> sdivrem(uint128 x, uint128 y) noexcept
     return {q_is_neg ? -res.quot : res.quot, x_is_neg ? -res.rem : res.rem};
 }
 
-inline uint128 operator/(uint128 x, uint128 y) noexcept
+inline constexpr uint128 operator/(uint128 x, uint128 y) noexcept
 {
     return udivrem(x, y).quot;
 }
 
-inline uint128 operator%(uint128 x, uint128 y) noexcept
+inline constexpr uint128 operator%(uint128 x, uint128 y) noexcept
 {
     return udivrem(x, y).rem;
 }
 
-inline uint128& operator/=(uint128& x, uint128 y) noexcept
+inline constexpr uint128& operator/=(uint128& x, uint128 y) noexcept
 {
     return x = x / y;
 }
 
-inline uint128& operator%=(uint128& x, uint128 y) noexcept
+inline constexpr uint128& operator%=(uint128& x, uint128 y) noexcept
 {
     return x = x % y;
 }
@@ -1001,8 +1003,9 @@ struct uint
 
     constexpr explicit operator bool() const noexcept { return *this != uint{}; }
 
+    /// Explicit converting operator to smaller uint types.
     template <unsigned M>
-    explicit operator uint<M>() const noexcept
+    constexpr explicit operator uint<M>() const noexcept
         requires(M < N)
     {
         uint<M> r;
@@ -1013,7 +1016,7 @@ struct uint
 
     /// Explicit converting operator for all builtin integral types.
     template <typename Int>
-    explicit operator Int() const noexcept
+    constexpr explicit operator Int() const noexcept
         requires(std::is_integral_v<Int>)
     {
         static_assert(sizeof(Int) <= sizeof(uint64_t));

test/unittests/test_div.cpp

@@ -446,6 +446,8 @@ inline uint64_t reciprocal_naive(uint64_t d) noexcept
 
 TEST(div, reciprocal)
 {
+    static_assert(reciprocal_2by1(0x8000000000000000) == 0xffffffffffffffff);
+
     constexpr auto n = 1000000;
 
     constexpr auto d_start = uint64_t{1} << 63;
@@ -466,6 +468,7 @@ TEST(div, reciprocal)
 TEST(div, reciprocal_3by2)
 {
     // Basic inputs for reciprocal_3by2() to make porting to other languages easier.
+    static_assert(reciprocal_3by2(0x80000000000000000000000000000000_u128) == 0xffffffffffffffff);
 
     EXPECT_EQ(reciprocal_3by2({0x0000000000000000, 0x8000000000000000}), 0xffffffffffffffffu);
     EXPECT_EQ(reciprocal_3by2({0x0000000000000001, 0x8000000000000000}), 0xffffffffffffffffu);

test/unittests/test_int128.cpp

@@ -235,6 +235,26 @@ TEST(int128, mul)
 
 TEST(int128, increment)
 {
+    static_assert([] {
+        uint128 x;
+        return ++x;
+    }() == 1);
+
+    static_assert([] {
+        uint128 x;
+        return x++;
+    }() == 0);
+
+    static_assert([] {
+        uint128 x = 1;
+        return --x;
+    }() == 0);
+
+    static_assert([] {
+        uint128 x = 1;
+        return x++;
+    }() == 1);
+
     constexpr auto IO = uint128{0, 1};
     constexpr auto Of = uint128{~uint64_t{0}};
 
@@ -307,6 +327,16 @@ TEST(int128, shr)
 
 TEST(int128, div)
 {
+    static_assert(7_u128 / 3_u128 == 2_u128);
+    static_assert(7_u128 % 3_u128 == 1_u128);
+    static_assert(udivrem(7, 3) == div_result<uint128>{2, 1});
+    static_assert(udivrem(0x10000000000000000_u128, 0x20000000000000000_u128) ==
+                  div_result<uint128>{0, 0x10000000000000000_u128});
+    static_assert(udivrem(0x80000000000000000000000000000002_u128,
+                      0x80000000000000000000000000000000_u128) == div_result<uint128>{1, 2});
+    static_assert(udivrem(0x70000000000000000_u128, 0x20000000000000000_u128) ==
+                  div_result<uint128>{3, 0x10000000000000000_u128});
+
     int index = 0;
     for (const auto& t : div_test_cases)
     {
@@ -326,6 +356,10 @@ TEST(int128, div)
 
 TEST(int128, sdivrem)
 {
+    static_assert(
+        sdivrem(0x33c7c3442a47d644b0d0b4ca50f8bbe1_u128, 0x5d99de82798cc77d06c05e7aa7c1f54_u128) ==
+        div_result<uint128>{8, 0x4fad402ed8172862d70858cfd17c141_u128});
+
     const auto x = 0x83017fa6deecda0063b1977_u128;
     const auto y = 0x1bc83504ea8f7_u128;
 

test/unittests/test_intx_api.cpp

@@ -292,8 +292,30 @@ TYPED_TEST(uint_api, bitwise_op_assignment)
     EXPECT_EQ(x >>= x, 0);
 }
 
+TYPED_TEST(uint_api, explicit_conversion_to_smaller_uint)
+{
+    if constexpr (TypeParam::num_bits > 128)
+    {
+        using SmallerType = intx::uint<TypeParam::num_bits - 64>;
+        static_assert(static_cast<SmallerType>(TypeParam{1}) == 1);
+
+        TypeParam x;
+        for (size_t i = 0; i < TypeParam::num_words; ++i)
+            x[i] = i + 1;
+
+        const auto smaller = static_cast<SmallerType>(x);
+        for (size_t i = 0; i < SmallerType::num_words; ++i)
+        {
+            EXPECT_EQ(smaller[i], i + 1);
+        }
+    }
+}
+
 TYPED_TEST(uint_api, explicit_conversion_to_integral_type)
 {
+    static_assert(
+        static_cast<uint32_t>(TypeParam{0x0102030405060708, 0xffffffffffffffff}) == 0x05060708);
+
     TypeParam x;
     x[0] = 3;
     x[1] = 0xffffffffffffffff;