refactor: modernize the implementation of uint256.*

- Constructors of uint256 to utilize Span instead of requiring a std::vector
- converts m_data into a std::array
- Prefers using `WIDTH` instead of `sizeof(m_data)`
- make all the things constexpr
- replace C style functions with c++ equivalents
    - memset -> std::fill
    - memcpy -> std::copy
        Note: In practice, implementations of std::copy avoid multiple assignments and use bulk copy functions such as std::memmove if the value type is TriviallyCopyable and the iterator types satisfy LegacyContiguousIterator. (https://en.cppreference.com/w/cpp/algorithm/copy)
    - memcmp -> std::memcmp

5 files changed, 38 insertions, 61 deletions

diff --git a/src/consensus/params.h b/src/consensus/params.h
index 7c35222713..3b5eb1034d 100644
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -11,6 +11,7 @@
 #include <chrono>
 #include <limits>
 #include <map>
+#include <vector>
 
 namespace Consensus {
 
diff --git a/src/psbt.h b/src/psbt.h
index b636f0348b..f1f04cccef 100644
--- a/src/psbt.h
+++ b/src/psbt.h
@@ -889,7 +889,7 @@ struct PSBTOutput
                     } else if (key.size() != 33) {
                         throw std::ios_base::failure("Output Taproot BIP32 keypath key is not at 33 bytes");
                     }
-                    XOnlyPubKey xonly(uint256({key.begin() + 1, key.begin() + 33}));
+                    XOnlyPubKey xonly(uint256(Span<uint8_t>(key).last(32)));
                     std::set<uint256> leaf_hashes;
                     uint64_t value_len = ReadCompactSize(s);
                     size_t before_hashes = s.size();
diff --git a/src/random.h b/src/random.h
index 5fe20c5f76..082ccd4047 100644
--- a/src/random.h
+++ b/src/random.h
@@ -15,6 +15,7 @@
 #include <chrono>
 #include <cstdint>
 #include <limits>
+#include <vector>
 
 /**
  * Overall design of the RNG and entropy sources.
diff --git a/src/uint256.cpp b/src/uint256.cpp
index cd9cbb566a..7f81c3c448 100644
--- a/src/uint256.cpp
+++ b/src/uint256.cpp
@@ -7,15 +7,6 @@
 
 #include <util/strencodings.h>
 
-#include <string.h>
-
-template <unsigned int BITS>
-base_blob<BITS>::base_blob(const std::vector<unsigned char>& vch)
-{
-    assert(vch.size() == sizeof(m_data));
-    memcpy(m_data, vch.data(), sizeof(m_data));
-}
-
 template <unsigned int BITS>
 std::string base_blob<BITS>::GetHex() const
 {
@@ -29,7 +20,7 @@ std::string base_blob<BITS>::GetHex() const
 template <unsigned int BITS>
 void base_blob<BITS>::SetHex(const char* psz)
 {
-    memset(m_data, 0, sizeof(m_data));
+    std::fill(m_data.begin(), m_data.end(), 0);
 
     // skip leading spaces
     while (IsSpace(*psz))
@@ -43,7 +34,7 @@ void base_blob<BITS>::SetHex(const char* psz)
     size_t digits = 0;
     while (::HexDigit(psz[digits]) != -1)
         digits++;
-    unsigned char* p1 = (unsigned char*)m_data;
+    unsigned char* p1 = m_data.data();
     unsigned char* pend = p1 + WIDTH;
     while (digits > 0 && p1 < pend) {
         *p1 = ::HexDigit(psz[--digits]);
@@ -67,14 +58,12 @@ std::string base_blob<BITS>::ToString() const
 }
 
 // Explicit instantiations for base_blob<160>
-template base_blob<160>::base_blob(const std::vector<unsigned char>&);
 template std::string base_blob<160>::GetHex() const;
 template std::string base_blob<160>::ToString() const;
 template void base_blob<160>::SetHex(const char*);
 template void base_blob<160>::SetHex(const std::string&);
 
 // Explicit instantiations for base_blob<256>
-template base_blob<256>::base_blob(const std::vector<unsigned char>&);
 template std::string base_blob<256>::GetHex() const;
 template std::string base_blob<256>::ToString() const;
 template void base_blob<256>::SetHex(const char*);
diff --git a/src/uint256.h b/src/uint256.h
index e74b9ff7b1..782fec8e51 100644
--- a/src/uint256.h
+++ b/src/uint256.h
@@ -9,11 +9,12 @@
 #include <crypto/common.h>
 #include <span.h>
 
-#include <assert.h>
+#include <algorithm>
+#include <array>
+#include <cassert>
 #include <cstring>
 #include <stdint.h>
 #include <string>
-#include <vector>
 
 /** Template base class for fixed-sized opaque blobs. */
 template<unsigned int BITS>
@@ -21,7 +22,9 @@ class base_blob
 {
 protected:
     static constexpr int WIDTH = BITS / 8;
-    uint8_t m_data[WIDTH];
+    std::array<uint8_t, WIDTH> m_data;
+    static_assert(WIDTH == sizeof(m_data), "Sanity check");
+
 public:
     /* construct 0 value by default */
     constexpr base_blob() : m_data() {}
@@ -29,64 +32,47 @@ public:
     /* constructor for constants between 1 and 255 */
     constexpr explicit base_blob(uint8_t v) : m_data{v} {}
 
-    explicit base_blob(const std::vector<unsigned char>& vch);
+    constexpr explicit base_blob(Span<const unsigned char> vch)
+    {
+        assert(vch.size() == WIDTH);
+        std::copy(vch.begin(), vch.end(), m_data.begin());
+    }
 
-    bool IsNull() const
+    constexpr bool IsNull() const
     {
-        for (int i = 0; i < WIDTH; i++)
-            if (m_data[i] != 0)
-                return false;
-        return true;
+        return std::all_of(m_data.begin(), m_data.end(), [](uint8_t val) {
+            return val == 0;
+        });
     }
 
-    void SetNull()
+    constexpr void SetNull()
     {
-        memset(m_data, 0, sizeof(m_data));
+        std::fill(m_data.begin(), m_data.end(), 0);
     }
 
-    inline int Compare(const base_blob& other) const { return memcmp(m_data, other.m_data, sizeof(m_data)); }
+    constexpr int Compare(const base_blob& other) const { return std::memcmp(m_data.data(), other.m_data.data(), WIDTH); }
 
-    friend inline bool operator==(const base_blob& a, const base_blob& b) { return a.Compare(b) == 0; }
-    friend inline bool operator!=(const base_blob& a, const base_blob& b) { return a.Compare(b) != 0; }
-    friend inline bool operator<(const base_blob& a, const base_blob& b) { return a.Compare(b) < 0; }
+    friend constexpr bool operator==(const base_blob& a, const base_blob& b) { return a.Compare(b) == 0; }
+    friend constexpr bool operator!=(const base_blob& a, const base_blob& b) { return a.Compare(b) != 0; }
+    friend constexpr bool operator<(const base_blob& a, const base_blob& b) { return a.Compare(b) < 0; }
 
     std::string GetHex() const;
     void SetHex(const char* psz);
     void SetHex(const std::string& str);
     std::string ToString() const;
 
-    const unsigned char* data() const { return m_data; }
-    unsigned char* data() { return m_data; }
+    constexpr const unsigned char* data() const { return m_data.data(); }
+    constexpr unsigned char* data() { return m_data.data(); }
 
-    unsigned char* begin()
-    {
-        return &m_data[0];
-    }
+    constexpr unsigned char* begin() { return m_data.data(); }
+    constexpr unsigned char* end() { return m_data.data() + WIDTH; }
 
-    unsigned char* end()
-    {
-        return &m_data[WIDTH];
-    }
+    constexpr const unsigned char* begin() const { return m_data.data(); }
+    constexpr const unsigned char* end() const { return m_data.data() + WIDTH; }
 
-    const unsigned char* begin() const
-    {
-        return &m_data[0];
-    }
+    static constexpr unsigned int size() { return WIDTH; }
 
-    const unsigned char* end() const
-    {
-        return &m_data[WIDTH];
-    }
-
-    static constexpr unsigned int size()
-    {
-        return sizeof(m_data);
-    }
-
-    uint64_t GetUint64(int pos) const
-    {
-        return ReadLE64(m_data + pos * 8);
-    }
+    constexpr uint64_t GetUint64(int pos) const { return ReadLE64(m_data.data() + pos * 8); }
 
     template<typename Stream>
     void Serialize(Stream& s) const
@@ -107,8 +93,8 @@ public:
  */
 class uint160 : public base_blob<160> {
 public:
-    constexpr uint160() {}
-    explicit uint160(const std::vector<unsigned char>& vch) : base_blob<160>(vch) {}
+    constexpr uint160() = default;
+    constexpr explicit uint160(Span<const unsigned char> vch) : base_blob<160>(vch) {}
 };
 
 /** 256-bit opaque blob.
@@ -118,9 +104,9 @@ public:
  */
 class uint256 : public base_blob<256> {
 public:
-    constexpr uint256() {}
+    constexpr uint256() = default;
     constexpr explicit uint256(uint8_t v) : base_blob<256>(v) {}
-    explicit uint256(const std::vector<unsigned char>& vch) : base_blob<256>(vch) {}
+    constexpr explicit uint256(Span<const unsigned char> vch) : base_blob<256>(vch) {}
     static const uint256 ZERO;
     static const uint256 ONE;
 };