uint256: Add constexpr ctor taking 4 uint64_t

hodlinator · Jul 17, 2024 · f957901 · f957901
1 parent c3a9c71
commit f957901
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Showing 3 changed files with 30 additions and 2 deletions.
diff --git a/src/kernel/chainparams.cpp b/src/kernel/chainparams.cpp
@@ -76,9 +76,9 @@ class CMainParams : public CChainParams {
         consensus.signet_challenge.clear();
         consensus.nSubsidyHalvingInterval = 210000;
         consensus.script_flag_exceptions.emplace( // BIP16 exception
-            uint256S("0x00000000000002dc756eebf4f49723ed8d30cc28a5f108eb94b1ba88ac4f9c22"), SCRIPT_VERIFY_NONE);
+            uint256{0x00000000000002dc, 0x756eebf4f49723ed, 0x8d30cc28a5f108eb, 0x94b1ba88ac4f9c22}, SCRIPT_VERIFY_NONE);
         consensus.script_flag_exceptions.emplace( // Taproot exception
-            uint256S("0x0000000000000000000f14c35b2d841e986ab5441de8c585d5ffe55ea1e395ad"), SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS);
+            uint256{0x0000000000000000, 0x000f14c35b2d841e, 0x986ab5441de8c585, 0xd5ffe55ea1e395ad}, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS);
         consensus.BIP34Height = 227931;
         consensus.BIP34Hash = uint256S("0x000000000000024b89b42a942fe0d9fea3bb44ab7bd1b19115dd6a759c0808b8");
         consensus.BIP65Height = 388381; // 000000000000000004c2b624ed5d7756c508d90fd0da2c7c679febfa6c4735f0

diff --git a/src/test/uint256_tests.cpp b/src/test/uint256_tests.cpp
@@ -329,4 +329,16 @@ BOOST_AUTO_TEST_CASE( check_ONE )
     BOOST_CHECK_EQUAL(one, uint256::ONE);
 }
 
+BOOST_AUTO_TEST_CASE( check_uint256_uint64_t )
+{
+    // Forces compile time evaluation
+    auto compile_time = [] (auto input) consteval {
+        return input;
+    };
+
+    const uint256 runtime_string = uint256S("4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b");
+    constexpr uint256 uint64_ctor{compile_time(uint256{0x4a5e1e4baab89f3a, 0x32518a88c31bc87f, 0x618f76673e2cc77a, 0xb2127b7afdeda33b})};
+    BOOST_CHECK_EQUAL(runtime_string, uint64_ctor);
+}
+
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/uint256.h b/src/uint256.h
@@ -23,6 +23,7 @@ class base_blob
 protected:
     static constexpr int WIDTH = BITS / 8;
     static_assert(BITS % 8 == 0, "base_blob currently only supports whole bytes.");
+    static_assert(WIDTH > 0, "base_blob currently only supports non-zero width.");
     std::array<uint8_t, WIDTH> m_data;
     static_assert(WIDTH == sizeof(m_data), "Sanity check");
 
@@ -39,6 +40,19 @@ class base_blob
         std::copy(vch.begin(), vch.end(), m_data.begin());
     }
 
+    // Uses std::span instead of Span to get rbegin() & rend().
+    constexpr explicit base_blob(std::span<const uint64_t> parts)
+        requires(BITS % 64 == 0)
+    {
+        assert(parts.size() * sizeof(parts[0]) == WIDTH);
+        auto writeIt = m_data.begin();
+        for (auto partIt = parts.rbegin(); partIt != parts.rend(); ++partIt) {
+            for (unsigned bitOffset = 0; bitOffset < 64; bitOffset += 8) {
+                *(writeIt++) = (*partIt >> bitOffset) & 0xFF;
+            }
+        }
+    }
+
     constexpr bool IsNull() const
     {
         return std::all_of(m_data.begin(), m_data.end(), [](uint8_t val) {
@@ -106,6 +120,8 @@ class uint256 : public base_blob<256> {
 public:
     constexpr uint256() = default;
     constexpr explicit uint256(uint8_t v) : base_blob<256>(v) {}
+    // Currently implicitly constructs an intermediate std::vector using extra curly-braces until, see C++ P2447R6.
+    constexpr explicit uint256(uint64_t a, uint64_t b, uint64_t c, uint64_t d) : base_blob<256>{std::span<const uint64_t>{{a, b, c, d}}} {}
     constexpr explicit uint256(Span<const unsigned char> vch) : base_blob<256>(vch) {}
     static const uint256 ZERO;
     static const uint256 ONE;